ABSTRACT
CHAPTER-1
WIRELESS COMMUNICATION - LASER COMMUNICATION
1.1 INTRODUCTION:
Communication technology has experienced a continual development to higher and higher carrier frequencies, starting from a few hundred kilohertz at Marconi's time to several hundred terahertzes since we employ lasers in fiber systems. The main driving force was that the usable bandwidth - and hence transmission capacity - increases proportional to the carrier frequency. Another asset comes into play in free-space point-to-point links. The minimum divergence obtainable with a freely propagating beam of electromagnetic waves scales proportional to the wavelength. The jump from microwaves to light waves therefore means a reduction in beam width by orders of magnitude, even if we use transmit antennas of much smaller diameter. The reduced beam width does not only imply increased intensity at the receiver site but also reduced cross talk between closely operating links and less chance for eavesdropping.
For the past quarter century, wireless communication has been hailed as the superior method for transmitting video, audio, data and various analog signals. Laser offers many well-known advantages over twisted pair and coaxial cable, including immunity to electrical interference and superior bandwidth. For these and many other reasons, wireless transmission systems have been increasingly integrated into a wide range of applications across many industries.
Now, a new generation of products that employs pure digital signaling to transmit analog information offers the opportunity to raise the standard once again, bringing wireless transmission to a whole new level.
Digital systems offer superior performance, flexibility and reliability, and yet don’t cost any more than the older analog designs they replace. This Education Guide examines how digital signaling over laser is accomplished and the resulting benefits, both from a performance and economic perspective.
1.2 LASER APPLICATIONS:
Why Laser Instead of RF?
• Power Consumption :
RF network needs to constantly listen, depending on the duty cycle. This takes power. A laser node however does not need to listen, and can sleep while waiting for a laser pulse.
• Range:
A RF enabled node has a limited range. A laser has a range in the kilometers. This means a node can be far away from the central network nodes.
• Low cost and reliable:
Laser communication system is basically cheaper in comparison to lying of optical fiber and maintaining it. Wireless communication system has initial value but it is quite reliable and of many usage at a time as digital as well as voice transmission through a single transmitter. Hence quite more effective
CHAPTER -2
LASER COMMUNICATION WITH CONTROL SYSTEM
1. PROJECT GOALS
The goal of our project is to develop a low powered, inexpensive, and versatile optical wireless communication system. Such a system should be able to send transmission messages using lasers, and should be low powered, especially compared to radio frequency based wireless communications. Our goal is to create and design a versatile system so that the system can be used for different types of wireless networks, including IP based networks and wireless sensor networks.
Our primary objective is to develop a working system that can achieve wireless communication over laser. This entails the design and development of the hardware, data link, and physical layers of the system. This includes the data network protocols, including the method of using the laser to transmit information over air. We also need to design the higher level network protocols, such that data frames can be transferred over the data link layers. A secondary goal will be to compare and contrast the power consumption of the optical wireless communication system against a typical RF wireless communication system. We seek to demonstrate that for some wireless applications, an optical wireless system holds
Certain advantages in terms of power and other characteristics. It is our goal as well to develop a framework for further research and analysis into such a system, and making one actually viable.
Overall we seek to develop a working communication system where two nodes can transfer data (in the form of bytes) to each other using laser pulses, and demonstrate that such a system can indeed work. In this paper, we will explain the motivation for such a system, where a laser based network has advantages over traditional RF ones, and how we implemented our prototype network.
2.2 PROJECT BACKGROUND
Wireless communications has become increasingly important in technology, communication, and computer science. From cell phones to wireless internet to home devices, everything is being converted from wired into wireless. A major research and focus area in fact has been the wireless sensor network. This network relies on low powered self-contained nodes that sense the environment, such as temperature or humidity. These nodes must be able to transfer and receive information wirelessly. Indeed, a lot of research and funding has been put into developing wireless systems. Most of the focus has gone to radio frequency wireless communication.
All spacecrafts flying at present communicates with ground by means of a radio communication link. This link consists of an onboard radio transmitter/receiver coupled to a single or two antennas. The ground station has a similar system. The radio-beam that leaves the antenna will attenuate over distance following the r-2, just like light from a flashlight. For satellites in low earth orbit, i.e. altitudes between 200 and 2000km, the onboard antenna system is typically a simple dipole or quadropole antenna,
Enabling omnidirectional communication, i.e. without pointing the
Antenna towards the receiver. This approach is viable because the distance is small, and, because the data rate typically is moderate.
For higher orbit, e.g. geostationary satellites, the downlink antennas are typically highly directional, e.g. dish- or cluster-antennas. Such antenna systems have the benefit of “focusing” the radio energy into a narrow beam before the wave’s leaves the antenna. As soon as the waves leaves the antenna dominated space (far field approximation) the beam is still attenuated according to the r- 2 law, but as the intrinsic energy is higher in certain directions, more energy/m-2 will be observed in these directions. Obviously, such antennas must be pointed at the ground station in order to work, and this pointing action requires either the satellite to track the station or to have a moving gimbal mounted antenna system. The spacecraft uplink antenna does not need high directionality (gain), because the ground
Segment usually utilizes large antennas and powerful transmitters such that an ample radio energy density (W/m-2) arrives at the spacecraft receiver antenna. Conversely, the spacecraft are bound to use low power transmitters, partly because electrical power is a scarce resource in space, partly because high power transmitters are heavy, large, and have a short life. Deep space probes, that are spacecrafts that are bound for the Moon and beyond, are forced to use highly directional antennas both for up- and downlink because of the large distance between the spacecraft and the ground station. E.g. spacecrafts bound for Mars will have 2- 4m diameter dish antennas on the spacecraft, and the ground segment uses 70m antennas! The size of the antenna determines, together with the frequency of the radio waves, the
Directionality (i.e. gain) of the antenna (3dB beam width = 708/antenna diameter degrees).
The larger the antenna, and the higher the frequency, the higher gain. Therefore, there has been a constant drive for use of higher frequencies to enable smaller antenna systems onboard the spacecraft. At present, 20-30 GHz is practical. Finally, the required data rate that the communication link has to support depends on the total attenuation of the link because certain energy must be received per bit. Hence, if the powers received are low, it will take longer time to achieve the necessary energy, and vise
2.3 SYSTEM OVERVIEW & DESCRIPTION
2.3.1 Overview
• Background
• Project goals
• Motivation and Challenges
• Project implementation
• Data flow
• Encoding scheme
• Framing scheme
2.3.2 Background
There has been a shift from wired to wireless
A lot of research has been put into Radiofrequency (RF) wireless. But not much on optical wireless
3. Project goals
Develop a wireless optical communication
System using laser
A) Low-powered
b) Inexpensive
c) Versatile
4. Motivations and Challenges
Laser offers the following benefits
1. Long range
2. Low-powered, low interference
3. Narrow beam very hard to detect & intercept
4. High speed
Laser has the following disadvantage
1. Non-mobile
2. Line of sight issue
3. Challenges
4. Design a reliable coding scheme
5. Optimize for bandwidth and latency
.
5. Project Implementation
Composed of two Parts
1. Laser boards – the data link and physical layer
2. Transmitter & receiver scale - the network and application layer
2.3.6 Data Flow
1. Framed bytes
2. Encoded bits
3. Framed bytes
6. Result – what did we accomplish
1. Implemented a basic laser communication
System
2. Can send data from one Scale to another
3. Input data can be from a file or from command
Line
4. Can use the system to trigger command line
Execution remotely
2.3.8 Future works
1. Improve latency and bandwidth
2. Support full-duplex communication
3. Support multiple senders/receivers
4. Improve encoding and framing schemes
5. Error detection/correction
6. Extensive power-usage analysis of the system
7. More fully develop laser network stack
CHAPTER-3
COMPONENTS
3.1 COMPONENTS USED:
• PCB
• STEP DOWN TRANSFORMER 5V/500mA
• VOLTAGE REGULATOR LM7805
• RECTIFIER DIODES 1N4001
• ELECTROLYTIC CAPACITORS
• LED DISPLAY
• LEDs
• IC 7447, 8870, 91214.
• Tr. BC-548
• Laser diode
• OPERATIONAL AMPLIFIER
• PVC WIRES
• RESSISTANCE 10K
• CAPACITOR 104PF
• DPDT S/W
• IC 7805
• MICRO SWITCH
• CRYSTAL 12 MHZ
• RESET 100K
• MIKE
• SPEAKER 5 OHM
3.2 DESCRIPTION ABOUT THE COMPONENTS
3.2.1 PCB:
PCBs are boards whereupon electronic circuits have been etched. PCBs are rugged, inexpensive, and can be highly reliable. They require much more layout effort and higher initial cost than either wire-wrapped or point-to-point constructed circuits, but are much cheaper and faster for high-volume production. Much of the electronics industry's PCB design, assembly, and quality control needs are set by standards that are published by the IPC organization.
After the printed circuit board (PCB) is completed, electronic components must be attached to form a functional printed circuit assembly, or PCA (sometimes called a "printed circuit board assembly" PCBA). In through-hole construction, component leads are inserted in holes. In surface-mount construction, the components are placed on pads or lands on the outer surfaces of the PCB. In both kinds of construction, component leads are electrically and mechanically fixed to the board with a molten metal solder.
There are a variety of soldering techniques used to attach components to a PCB. High volume production is usually done with machine placement and bulk wave soldering or reflow ovens, but skilled technicians are able to solder very tiny parts (for instance 0201 packages which are 0.02" by 0.01") by hand under a microscope, using tweezers and a fine tip soldering iron for small volume prototypes. Some parts are impossible to solder by hand, such as ball grid array (BGA) packages.
Often, through-hole and surface-mount construction must be combined in a single PCA because some required components are available only in surface-mount packages, while others are available only in through-hole packages. Another reason to use both methods is that through-hole mounting can provide needed strength for components likely to endure physical stress, while components that are expected to go untouched will take up less space using surface-mount techniques.
After the board has been populated it may be tested in a variety of ways:
• While the power is off, visual inspection, automated optical inspection. JEDEC guidelines for PCB component placement, soldering, and inspection are commonly used to maintain quality control in this stage of PCB manufacturing.
• While the power is off, analog signature analysis, power-off testing.
• While the power is on, in-circuit tests, where physical measurements (i.e. voltage, frequency) can be done.
• While the power is on, functional test, just checking if the PCB does what it had been designed for.
To facilitate these tests, PCBs may be designed with extra pads to make temporary connections. Sometimes these pads must be isolated with resistors. The in-circuit test may also exercise boundary scan test features of some components. In-circuit test systems may also be used to program nonvolatile memory components on the board.
In boundary scan testing, test circuits integrated into various ICs on the board form temporary connections between the PCB traces to test that the ICs are mounted correctly. Boundary scan testing requires that all the ICs to be tested use a standard test configuration procedure, the most common one being the Joint Test Action Group (JTAG) standard. When boards fail the test, technicians may disorder and replace failed components, a task known as "rework".
Manufacturing
a) Materials: Conducting layers are typically made of thin copper foil. Insulating layers dielectric are typically laminated together with epoxy resin prepare. The board is typically coated with a solder mask that is green in color. Other colors that are normally available are blue, and red. There are quite a few different dielectrics that can be chosen to provide different insulating values depending on the requirements of the circuit. Some of these dielectrics are polytetrafluoroethylene, FR-4, FR-1, CEM-1 or CEM-3. Well known prepreg materials used in the PCB industry are FR-2 (Phenolic cotton paper), FR-3 (Cotton paper and epoxy), FR-4 (Woven glass and epoxy), FR-5 (Woven glass and epoxy), FR-6 (Matte glass and polyester), G-10 (Woven glass and epoxy), CEM-1 (Cotton paper and epoxy), CEM-2
(Cotton paper and epoxy), CEM-3 (Woven glass and epoxy), CEM-4 (Woven glass and epoxy), CEM-5 (Woven glass and polyester).
Typical density of a raw PCB (an average amount of traces, holes, and via's, with no components) is 2.15g / cm3
Patterning (etching) : The vast majority of printed circuit boards are made by bonding a layer of copper over the entire substrate, sometimes on both sides, (creating a "blank PCB") then removing unwanted copper after applying a temporary mask (eg. by etching), leaving only the desired copper traces. A few PCBs are made by adding traces to the bare substrate (or a substrate with a very thin layer of copper) usually by a complex process of multiple electroplating steps.
There are three common "subtractive" methods (methods that remove copper) used for the production of printed circuit boards:
1. Silk screen printing uses etch-resistant inks to protect the copper foil. Subsequent etching removes the unwanted copper. Alternatively, the ink may be conductive, printed on a blank (non-conductive) board. The latter technique is also used in the manufacture of hybrid circuits.
2. Photoengraving uses a photomask and chemical etching to remove the copper foil from the substrate. The photomask is usually prepared with a photoplotter from data produced by a technician using CAM, or computer-aided manufacturing software. Laser-printed transparencies are typically employed for phototools; however, direct laser imaging techniques are being employed to replace phototools for high-resolution requirements.
3. PCB milling uses a two or three-axis mechanical milling system to mill away the copper foil from the substrate. A PCB milling machine (referred to as a 'PCB Prototyper') operates in a similar way to a plotter, receiving commands from the host software that control the position of the milling head in the x, y, and (if relevant) z axis. Data to drive the Prototyper is extracted from files generated in PCB design software and stored in HPGL or Gerber file format.
"Additive" processes also exist. The most common is the "semi-additive" process. In this version, the unpatterned board has a thin layer of copper already on it. A reverse mask is then applied. (Unlike a subtractive process mask, this mask exposes those parts of the substrate that will eventually become the traces.) Additional copper is then plated onto the board in the unmasked areas; copper may be plated to any desired weight. Tin-lead or other surface platings are then applied. The mask is stripped away and a brief etching step removes the now-exposed original copper laminate from the board, isolating the individual traces.
The additive process is commonly used for multi-layer boards as it facilitates the plating-through of the holes (to produce conductive vias) in the circuit board.
Lamination
Some PCBs have trace layers inside the PCB and are called multi-layer PCBs. These are formed by bonding together separately etched thin boards.
Drilling
Holes through a PCB are typically drilled with tiny drill bits made of solid tungsten carbide. The drilling is performed by automated drilling machines with placement controlled by a drill tape or drill file. These computer-generated files are also called numerically controlled drill (NCD) files or "Excellon files". The drill file describes the location and size of each drilled hole. These holes are often filled with annular rings to create vias. Vias allow the electrical and thermal connection of conductors on opposite sides of the PCB.
When very small vias are required, drilling with mechanical bits is costly because of high rates of wear and breakage. In this case, the vias may be evaporated by lasers. Laser-drilled vias typically have an inferior surface finish inside the hole. These holes are called micro vias.
It is also possible with controlled-depth drilling, laser drilling, or by pre-drilling the individual sheets of the PCB before lamination, to produce holes that connect only some of the copper layers, rather than passing through the entire board. These holes are called blind vias when they connect an internal copper layer to an outer layer, or buried vias when they connect two or more internal copper layers and no outer layers.
The walls of the holes, for boards with 2 or more layers, are plated with copper to form plated-through holes that electrically connect the conducting layers of the PCB. For multilayer boards, those with 4 layers or more, drilling typically produces a smear comprised of the bonding agent in the laminate system. Before the holes can be plated through, this smear must be removed by a chemical de-smear process, or by plasma-etch.
Test
Unpopulated boards may be subjected to a bare-board test where each circuit connection (as defined in a netlist) is verified as correct on the finished board. For high-volume production, a Bed of nails tester, a fixture or a Rigid needle adapter is used to make contact with copper lands or holes on one or both sides of the board to facilitate testing. A computer will instruct the electrical test unit to apply a small voltage to each contact point on the bed-of-nails as required, and verify that such voltage appears at other appropriate contact points. A "short" on a board would be a connection where there should not be one; an "open" is between two points that should be connected but are not. For small- or medium-volume boards, flying-probe and flying-grid testers use moving test heads to make contact with the copper/silver/gold/solder lands or holes to verify the electrical connectivity of the board under test.
[pic]
FIG; 3.2.1: PCB BOARD
3.2.2 STEP DOWN TRANSFORMER:
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors — the transformer's coils or "windings". Except for air-core transformers, the conductors are commonly wound around a single iron-rich core, or around separate but magnetically-coupled cores. A varying current in the first or "primary" winding creates a varying magnetic field in the core (or cores) of the transformer. This varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the "secondary" winding. This effect is called mutual induction.
If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will flow from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (VS) is in proportion to the primary voltage (VP), and is given by the ratio of the number of turns in the secondary to the number of turns in the primary as follows:
Vs/Vp=Ns/Np eqn (3.1)
By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be "stepped up" by making NS greater than NP, or "stepped down" by making NS less than NP. Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of national power grids. All operate with the same basic principles, although the range of designs is wide. While new technologies have eliminated the need for transformers in some electronic circuits, transformers are still found in nearly all electronic devices designed for household ("mains") voltage. Transformers are essential for high voltage power transmission, which makes long distance transmission economically practical.
. [pic]
FIG; 3.2.2 : STEP DOWN TRANSFORMER
The transformer is based on two principles: firstly, that an electric current can produce a magnetic field (electromagnetism) and secondly that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction). Changing the current in the primary coil changes the magnitude of the applied magnetic field. The changing magnetic flux extends to the secondary coil where a voltage is induced across its ends.
A simplified transformer design is shown to the left. A current passing through the primary coil creates a magnetic field. The primary and secondary coils are wrapped around a core of very high magnetic permeability, such as iron; this ensures that most of the magnetic field lines produced by the primary current are within the iron and pass through the secondary coil as well as the primary coil.
INDUCTION LAW --The voltage induced across the secondary coil may be calculated from Faraday's law of induction, which states that:
[pic] eqn (3.2)
where VS is the instantaneous voltage, NS is the number of turns in the secondary coil and Φ equals the magnetic flux through one turn of the coil. If the turns of the coil are oriented perpendicular to the magnetic field lines, the flux is the product of the magnetic field strength B and the area A through which it cuts. The area is constant, being equal to the cross-sectional area of the transformer core, whereas the magnetic field varies with time according to the excitation of the primary. Since the same magnetic flux passes through both the primary and secondary coils in an ideal transformer, the instantaneous voltage across the primary winding equals
[pic] eqn (3.2.a)
Taking the ratio of the two equations for VS and VP gives the basic equation for stepping up or stepping down the voltage
[pic] eqn (3.2.b)
3.2.3 Linear regulator
In electronics, a linear regulator is a voltage regulator based on an active device (such as a bipolar junction transistor, field effect transistor or vacuum tube) operating in its "linear region" (in contrast, a switching regulator is based on a transistor forced to act as an on/off switch) or passive devices like zener diodes operated in their breakdown region. The regulating device is made to act like a variable resistor, continuously adjusting a voltage divider network to maintain a constant output voltage.
Overview
The transistor (or other device) is used as one half of a potential divider to control the output voltage, and a feedback circuit compares the output voltage to a reference voltage in order to adjust the input to the transistor, thus keeping the output voltage reasonably constant. This is inefficient: since the transistor is acting like a resistor, it will waste electrical energy by converting it to heat. In fact, the power loss due to heating in the transistor is the current times the voltage dropped across the transistor. The same function can be performed more efficiently by a switched-mode power supply (SMPS), but it is more complex and the switching currents in it tend to produce electromagnetic interference. A SMPS can easily provide more than 30A of current at voltages as low as 3V, while for the same voltage and current, a linear regulator would be very bulky and heavy.
Linear regulators exist in two basic forms: series regulators and shunt regulators.
• Series regulators are the more common form. The series regulator works by providing a path from the supply voltage to the load through a variable resistance (the main transistor is in the "top half" of the voltage divider). The power dissipated by the regulating device is equal to the power supply output current times the voltage drop in the regulating device.
• The shunt regulator works by providing a path from the supply voltage to ground through a variable resistance (the main transistor is in the "bottom half" of the voltage divider). The current through the shunt regulator is diverted away from the load and flows uselessly to ground, making this form even less efficient than the series regulator. It is, however, simpler, sometimes consisting of just a voltage-reference diode, and is used in very low-powered circuits where the wasted current is too small to be of concern. This form is very common for voltage reference circuits.
All linear regulators require an input voltage at least some minimum amount higher than the desired output voltage. That minimum amount is called the drop-out voltage. For example, a common regulator such as the 7805 has an output voltage of 5V, but can only maintain this if the input voltage remains above about 7V. Its drop-out voltage is therefore 7V - 5V = 2V. When the supply voltage is less than about 2V above the desired output voltage, as is the case in low-voltage microprocessor power supplies, so-called low dropout regulators (LDOs) must be used.
Common solid-state series voltage regulators are the LM78xx (for positive voltages) and LM79xx (for negative voltages), and common fixed voltages are 5 V (for transistor-transistor logic circuits) and 12 V (for communications circuits and peripheral devices such as disk drives). In fixed voltage regulators the reference pin is tied to ground, whereas in variable regulators the reference pin is connected to the centre point of a fixed or variable voltage divider fed by the regulator's output. A variable voltage divider (such as a potentiometer) allows the user to adjust the regulated voltage.
3.2.3.1 SIMPLE ZENER REGULATOR
The image shows a simple zener voltage regulator. It is a shunt regulator and operates by way of the zener diode's action of maintaining a constant voltage across itself when the current through it is sufficient to take it into the zener breakdown region. The resistor R1 supplies the zener current IZ as well as the load current IR2 (R2 is the load). R1 can be calculated as -
[pic]
FIG;3.2.3 : ZENER REGULATOR
[pic] eqn (3.3)
where, VZ is the zener voltage, and IR2 is the required load current.
This regulator is used for very simple low power applications where the currents involved are very small and the load is permanently connected across the zener diode (such as voltage reference or voltage source circuits). Once R1 has been calculated, removing R2 will cause the full load current (plus the zener current) to flow through the diode and may exceed the diode's maximum current rating thereby damaging it. The regulation of this circuit is also not very good because the zener current (and hence the zener voltage) will vary depending on VS and inversely depending on the load current.
3.2.3.2 SIMPLE SERIES REGULATOR
Adding an emitter follower stage to the simple zener regulator forms a simple series voltage regulator and substantially improves the regulation of the circuit. Here, the load current IR2 is supplied by the transistor whose base is now connected to the zener diode. Thus the transistor's base current (IB) forms the load current for the zener diode and is much smaller than the current through R2. This regulator is classified as "series" because the regulating element, viz., the transistor, appears in series with the load. R1 sets the zener current (IZ) and is determined as –
[pic]
FIG; 3.2.4; SERIES REGULATOR
[pic] eqn (3.4)
where, VZ is the zener voltage, IB is the transistor's base current and K = 1.2 to 2 (to ensure that R1 is low enough for adequate IB).
[pic] eqn (3.5)
where, IR2 is the required load current and is also the transistor's emitter current (assumed to be equal to the collector current) and hFE(min) is the minimum acceptable DC current gain for the transistor.
3.2.4 RECTIFIER
A rectifier is an electrical device that converts alternating current (AC) to direct current (DC), a process known as rectification. Rectifiers have many uses including as components of power supplies and as detectors of radio signals. Rectifiers may be made of solid state diodes, vacuum tube diodes, mercury arc valves, and other components.
A device which performs the opposite function (converting DC to AC) is known as an inverter. When only one diode is used to rectify AC (by blocking the negative or positive portion of the waveform), the difference between the term diode and the term rectifier is merely one of usage, i.e., the term rectifier describes a diode that is being used to convert AC to DC. Almost all rectifiers comprise a number of diodes in a specific arrangement for more efficiently converting AC to DC than is possible with only one diode. Before the development of silicon semiconductor rectifiers, vacuum tube diodes and copper(I) oxide or selenium rectifier stacks were used.
Early radio receivers, called crystal radios, used a "cat's whisker" of fine wire pressing on a crystal of galena (lead sulfide) to serve as a point-contact rectifier or "crystal detector". In gas heating systems flame rectification can be used to detect a flame. Two metal electrodes in the outer layer of the flame provide a current path and rectification of an applied alternating voltage, but only while the flame is present.
3.2.4.1 Half Wave Rectification
In half wave rectification, either the positive or negative half of the AC wave is passed, while the other half is blocked. Because only one half of the input waveform reaches the output, it is very inefficient if used for power transfer. Half-wave rectification can be achieved with a single diode in a one-phase supply, or with three diodes in a three-phase supply.
[pic]
FIG; 3.2.5
3.2.4.2 Full-wave rectification
A full-wave rectifier converts the whole of the input waveform to one of constant polarity (positive or negative) at its output. Full-wave rectification converts both polarities of the input waveform to DC (direct current), and is more efficient. However, in a circuit with a non-center tapped transformer, four diodes are required instead of the one needed for half-wave rectification. (See semiconductors, diode). Four rectifiers arranged this way are called a diode bridge or bridge rectifier:
[pic]
FIG; 3.2.6
For single-phase AC, if the transformer is center-tapped, then two diodes back-to-back (i.e. anodes-to-anode or cathode-to-cathode) can form a full-wave rectifier. Twice as many windings are required on the transformer secondary to obtain the same output voltage compared to the bridge rectifier above.
FIG;3.2.7[pic]
[pic] eqn (3.6)
3.2.5 ELECTROLYTIC CAPACITOR
An electrolytic capacitor is a type of capacitor that uses an ionic conducting liquid as one of its plates with a larger capacitance per unit volume than other types. They are valuable in relatively high-current and low-frequency electrical circuits. This is especially the case in power-supply filters, where they store charge needed to moderate output voltage and current fluctuations in rectifier output. They are also widely used as coupling capacitors in circuits whereAC should be conducted but DC should not.
In aluminum electrolytic capacitors, the layer of insulating aluminum oxide on the surface of the aluminum plate acts as the dielectric, and it is the thinness of this layer that allows for a relatively high capacitance in a small volume. The aluminum oxide layer can withstand an electric field strength of the order of 109 volts per meter. The combination of high capacitance and high voltage result in high energy density.
Most electrolytic capacitors are polarized and may catastrophically fail if voltage is incorrectly applied. This is because a reverse-bias voltage above 1 to 1.5 V will destroy the center layer of dielectric material via electrochemical reduction (see redox reactions). Following the loss of the dielectric material, the capacitor will short circuit, and with sufficient short circuit current, the electrolyte will rapidly heat up and either leak or cause the capacitor to burst. To minimize the likelihood of a polarized electrolytic being incorrectly inserted into a circuit, polarity is indicated on the capacitor's exterior by a stripe with minus signs and possibly arrowheads adjacent to the negative lead or terminal. Also, the negative terminal lead of a radial electrolytic is shorter than the positive lead. On a printed circuit board, it is customary to indicate the correct orientation by using a square through-hole pad for the positive leadSpecial capacitors designed for AC operation are available, usually referred to as "non-polarized" or "NP" types. In these, full-thickness oxide layers are formed on both the aluminum foil strips prior to assembly. On the alternate halves of the AC cycles, one or the other of the foil strips acts as a blocking diode, preventing reverse current from damaging the electrolyte of the other one. Essentially, a 10 microfarad AC capacitor behaves like two 20 microfarad DC capacitors in inverse series.
And a round pad for the negative. Modern capacitors have a safety valve, typically either a scored section of the can, or a specially designed end seal to vent the hot gas/liquid, but ruptures can still be dramatic. An electrolytic can withstand a reverse bias for a short period of time, but will conduct significant current and not act as a very good capacitor. Most will survive with no reverse DC bias or with only AC voltage, but circuits should be designed so that there is not a constant reverse bias for any significant amount of time. A constant forward bias is preferable, and will increase the life of the capacitor.
3.2.6 LIGHT EMITTING DIODE
A light-emitting diode (LED) , is an electronic light source. The LED was first invented in Russia in the 1920s, and introduced in America as a practical electronic component in 1962. Oleg Vladimirovich Losev was a radio technician who noticed that diodes used in radio receivers emitted light when current was passed through them. In 1927, he published details in a Russian journal of the first ever LED. All early devices emitted low-intensity red light, but modern LEDs are available across the visible, ultraviolet and infra red wavelengths, with very high brightness.
LEDs are based on the semiconductor diode. When the diode is forward biased (switched on), electrons are able to recombine with holes and energy is released in the form of light. This effect is called electroluminescence and the color of the light is determined by the energy gap of the semiconductor. The LED is usually small in area (less than 1 mm2) with integrated optical components to shape its radiation pattern and assist in reflection.
LEDs present many advantages over traditional light sources including lower energy consumption, longer lifetime, improved robustness, smaller size and faster switching. However, they are relatively expensive and require more precise current and heat management than traditional light sources.
Applications of LEDs are diverse. They are used as low-energy and also for replacements for traditional light sources in well-established applications such as indicators and automotive lighting. The compact size of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are useful in communications technology.
[pic]
FIG;3.2.8(LED)
[pic]
LED SYMBOL
3.2.6 INTEGRATED CIRCUIT
In electronics, an integrated circuit (also known as IC, microcircuit, microchip, silicon chip, or chip) is a miniaturized electronic circuit (consisting mainly of semiconductor devices, as well as passive components) that has been manufactured in the surface of a thin substrate of semiconductor material. Integrated circuits are used in almost all electronic equipment in use today and have revolutionized the world of electronics.
A hybrid integrated circuit is a miniaturized electronic circuit constructed of individual semiconductor devices, as well as passive components, bonded to a substrate or circuit board.
[pic]
FIG;3.2.9(INTEGRATED CIRCUIT)
Integrated circuits were made possible by experimental discoveries which showed that semiconductor devices could perform the functions of vacuum tubes, and by mid-20th-century technology advancements in semiconductor device fabrication. The integration of large numbers of tiny transistors into a small chip was an enormous improvement over the manual assembly of circuits using discrete electronic components. The integrated circuit's mass production capability, reliability, and building-block approach to circuit design ensured the rapid adoption of standardized ICs in place of designs using discrete transistors. There are two main advantages of ICs over discrete circuits: cost and performance. Cost is low because the chips, with all their components, are printed as a unit by photolithography and not constructed one transistor at a time. Furthermore, much less material is used to construct a circuit as a packaged IC die than as a discrete circuit. Performance is high since the components switch quickly and consume little power (compared to their discrete counterparts), because the components are small and close together. As of 2006, chip areas range from a few square mm to around 350 mm², with up to 1 million transistors per mm².
Integrated circuits were made possible by experimental discoveries which showed that semiconductor devices could perform the functions of vacuum tubes, and by mid-20th-century technology advancements in semiconductor device fabrication. The integration of large numbers of tiny transistors into a small chip was an enormous improvement over the manual assembly of circuits using discrete electronic components. The integrated circuit's mass production capability, reliability, and building-block approach to circuit design ensured the rapid adoption of standardized ICs in place of designs using discrete transistors.
There are two main advantages of ICs over discrete circuits: cost and performance. Cost is low because the chips, with all their components, are printed as a unit by photolithography and not constructed one transistor at a time. Furthermore, much less material is used to construct a circuit as a packaged IC die than as a discrete circuit. Performance is high since the components switch quickly and consume little power (compared to their discrete counterparts), because the components are small and close together. As of 2006, chip areas range from a few square mm to around 350 mm², with up to 1 million transistors per mm².
.[pic]
FIG;3.2.8 (IC)
Invention
The integrated circuit was conceived by a radar scientist, Geoffrey W.A. Dummer (1909-2002), working for the Royal Radar Establishment of the British Ministry of Defence, and published at the Symposium on Progress in Quality Electronic Components in Washington, D.C. on May 7, 1952.He gave many symposia publicly to propagate his ideas. The integrated circuit can be credited as being invented by both Jack Kilby of Texas Instruments and Robert Noyce of Fairchild Semiconductor working independently of each other. Kilby recorded his initial ideas concerning the integrated circuit in July 1958 and successfully demonstrated the first working integrated circuit on September 12, 1958. Kilby won the 2000 Nobel Prize in Physics for his part of the invention of the integrated circuit. Robert Noyce also came up with his own idea of integrated circuit, half a year later than Kilby. Noyce's chip had solved many practical problems that the microchip developed by Kilby had not. Noyce's chip, made at Fairchild, was made of silicon, whereas Kilby's chip was made of germanium.
Early developments of the integrated circuit go back to 1949, when the German engineer Werner Jacobi (Siemens AG) filed a patent for an integrated-circuit-like semiconductor amplifying device showing five transistors on a common substrate arranged in a 2-stage amplifier arrangement. Jacobi discloses small and cheap hearing aids as typical industrial applications of his patent. A commercial use of his patent has not been reported.
A precursor idea to the IC was to create small ceramic squares (wafers), each one containing a single miniaturized component. Components could then be integrated and wired into a bidimensional or tridimensional compact grid. This idea, which looked very promising in 1957, was proposed to the US Army by Jack Kilby, and led to the short-lived Micromodule Program (similar to 1951's Project Tinkertoy). However, as the project was gaining momentum, Kilby came up with a new, revolutionary design: the IC.
Generations
SSI, MSI and LSI
The first integrated circuits contained only a few transistors. Called "Small-Scale Integration" (SSI), they used circuits containing transistors numbering in the tens.
SSI circuits were crucial to early aerospace projects, and vice-versa. Both the Minuteman missile and Apollo program needed lightweight digital computers for their inertial guidance systems; the Apollo guidance computer led and motivated the integrated-circuit technology, while the Minuteman missile forced it into mass-production.
These programs purchased almost all of the available integrated circuits from 1960 through 1963, and almost alone provided the demand that funded the production improvements to get the production costs from $1000/circuit (in 1960 dollars) to merely $25/circuit (in 1963 dollars). They began to appear in consumer products at the turn of the decade, a typical application being FM inter-carrier sound processing in television receivers.
The next step in the development of integrated circuits, taken in the late 1960s, introduced devices which contained hundreds of transistors on each chip, called "Medium-Scale Integration" (MSI).
They were attractive economically because while they cost little more to produce than SSI devices, they allowed more complex systems to be produced using smaller circuit boards, less assembly work (because of fewer separate components), and a number of other advantages.
Further development, driven by the same economic factors, led to "Large-Scale Integration" (LSI) in the mid 1970s, with tens of thousands of transistors per chip.
Integrated circuits such as 1K-bit RAMs, calculator chips, and the first microprocessors, that began to be manufactured in moderate quantities in the early 1970s, had under 4000 transistors. True LSI circuits, approaching 10000 transistors, began to be produced around 1974, for computer main memories and second-generation microprocessors.
VLSI
The final step in the development process, starting in the 1980s and continuing through the present, was "Very Large-Scale Integration" (VLSI). This could be said to start with hundreds of thousands of transistors in the early 1980s, and continues beyond several billion transistors as of 2007.
There was no single breakthrough that allowed this increase in complexity, though many factors helped. Manufacturing moved to smaller rules and cleaner fabs, allowing them to produce chips with more transistors with adequate yield, as summarized by the International Technology Roadmap for Semiconductors (ITRS). Design tools improved enough to make it practical to finish these designs in a reasonable time. The more energy efficient CMOS replaced NMOS and PMOS, avoiding a prohibitive increase in power consumption. Better texts such as the landmark textbook by Mead and Conway helped schools educate more designers, among other factors.
In 1986 the first one megabit RAM chips were introduced, which contained more than one million transistors. Microprocessor chips passed the million transistor mark in 1989 and the billion transistor mark in 2005. The trend continues largely unabated, with chips introduced in 2007 containing tens of billions of memory transistors .
ULSI, WSI, SOC and 3D-IC
To reflect further growth of the complexity, the term ULSI that stands for "Ultra-Large Scale Integration" was proposed for chips of complexity of more than 1 million transistors. To reflect further growth of the complexity, the term ULSI that stands for "Ultra-Large Scale Integration" was proposed for chips of complexity of more than 1 million transistors.
System-on-a-Chip (SoC or SOC) is an integrated circuit in which all the components needed for a computer or other system are included on a single chip. The design of such a device can be complex and costly, and building disparate components on a single piece of silicon may compromise the efficiency of some elements. However, these drawbacks are offset by lower manufacturing and assembly costs and by a greatly reduced power budget: because signals among the components are kept on-die, much less power is required (see Packaging, above).
Three Dimensional Integrated Circuit (3D-IC) has two or more layers of active electronic components that are integrated both vertically and horizontally into a single circuit. Communication between layers uses on-die signaling, so power consumption is much lower than in equivalent separate circuits. Judicious use of short vertical wires can substantially reduce overall wire length for faster operation.
Advances in integrated circuits
Among the most advanced integrated circuits are the microprocessors or "cores", which control everything from computers to cellular phones to digital microwave ovens. Digital memory chips and ASICs are examples of other families of integrated circuits that are important to the modern information society. While cost of designing and developing a complex integrated circuit is quite high, when spread across typically millions of production units the individual IC cost is minimized. The performance of ICs is high because the small size allows short traces which in turn allows low power logic (such as CMOS) to be used at fast switching speeds.
ICs have consistently migrated to smaller feature sizes over the years, allowing more circuitry to be packed on each chip. This increased capacity per unit area can be used to decrease cost and/or increase functionality—see Moore's law which, in its modern interpretation, states that the number of transistors in an integrated circuit doubles every two years. In general, as the feature size shrinks, almost everything improves—the cost per unit and the switching power consumption go down, and the speed goes up. However, ICs with nanometer-scale devices are not without their problems, principal among which is leakage current (see subthreshold leakage for a discussion of this), although these problems are not insurmountable and will likely be solved or at least ameliorated by the introduction of high-k dielectrics. Since these speed and power consumption gains are apparent to the end user, there is fierce competition among the manufacturers to use finer geometries. This process, and the expected progress over the next few years, is well described by the International Technology Roadmap for Semiconductors (ITRS).
Manufacture
Fabrication
The semiconductors of the periodic table of the chemical elements were identified as the most likely materials for a solid state vacuum tube by researchers like William Shockley at Bell Laboratories starting in the 1930s. Starting with copper oxide, proceeding to germanium, then silicon, the materials were systematically studied in the 1940s and 1950s. Today, silicon monocrystals are the main substrate used for integrated circuits (ICs) although some III-V compounds of the periodic table such as gallium arsenide are used for specialized applications like LEDs, lasers, solar cells and the highest-speed integrated circuits. It took decades to perfect methods of creating crystals without defects in the crystalline structure of the semiconducting material.
Semiconductor ICs are fabricated in a layer process which includes these key process steps:
a) Imaging
b) Deposition
c) Etching
The main process steps are supplemented by doping and cleaning. Mono-crystal silicon wafers (or for special applications, silicon on sapphire or gallium arsenide wafers) are used as the substrate. Photolithography is used to mark different areas of the substrate to be doped or to have polysilicon, insulators or metal (typically aluminum) tracks deposited on them.
• Integrated circuits are composed of many overlapping layers, each defined by photolithography, and normally shown in different colors. Some layers mark where various dopants are diffused into the substrate (called diffusion layers), some define where additional ions are implanted (implant layers), some define the conductors (polysilicon or metal layers), and some define the connections between the conducting layers (via or contact layers). All components are constructed from a specific combination of these layers.
• Capacitive structures, in form very much like the parallel conducting plates of a traditional electrical capacitor, are formed according to the area of the "plates", with insulating material between the plates. Capacitors of a wide range of sizes are common on ICs.
• Meandering stripes of varying lengths are sometimes used to form on-chip resistors, though most logic circuits do not need any resistors. The ratio of the length of the resistive structure to its width, combined with its sheet resistivity, determines the resistance.
• More rarely, inductive structures can be built as tiny on-chip coils, or simulated by gyrators.
A random access memory is the most regular type of integrated circuit; the highest density devices are thus memories; but even a microprocessor will have memory on the chip. (See the regular array structure at the bottom of the first image.) Although the structures are intricate – with widths which have been shrinking for decades – the layers remain much thinner than the device widths. The layers of material are fabricated much like a photographic process, although light waves in the visible spectrum cannot be used to "expose" a layer of material, as they would be too large for the features. Thus photons of higher frequencies (typically ultraviolet) are used to create the patterns for each layer. Because each feature is so small, electron microscopes are essential tools for a process engineer who might be debugging a fabrication process.
Each device is tested before packaging using automated test equipment (ATE), in a process known as wafer testing, or wafer probing. The wafer is then cut into rectangular blocks, each of which is called a die. Each good die (plural dice, dies, or die) is then connected into a package using aluminum (or gold) bond wires which are welded to pads, usually found around the edge of the die. After packaging, the devices go through final testing on the same or similar ATE used during wafer probing. Test cost can account for over 25% of the cost of fabrication on lower cost products, but can be negligible on low yielding, larger, and/or higher cost devices.
3.2.7 LASER DIODE
A laser diode is a laser where the active medium is a semiconductor similar to that found in a light-emitting diode. The most common and practical type of laser diode is formed from a p-n junction and powered by injected electric current. These devices are sometimes referred to as injection laser diodes to distinguish them from (optically) pumped laser diodes, which are more easily produced in the laboratory.
A laser diode, like many other semiconductor devices, is formed by doping a very thin layer on the surface of a crystal wafer. The crystal is doped to produce an n-type region and a p-type region, one above the other, resulting in a p-n junction, or diode.
The many types of diode lasers known today collectively form a subset of the larger classification of semiconductor p-n junction diodes. Just as in any semiconductor p-n junction diode, forward electrical bias causes the two species of charge carrier - holes and electrons - to be "injected" from opposite sides of the p-n junction into the depletion region, situated at its heart. Holes are injected from the p-doped, and electrons from the n-doped, semiconductor. (A depletion region, devoid of any charge carriers, forms automatically and unavoidably as a result of the difference in chemical potential between n- and p-type semiconductors wherever they are in physical contact.)
As charge injection is a distinguishing feature of diode lasers as compared to all other lasers, diode lasers are traditionally and more formally called "injection lasers." (This terminology differentiates diode lasers, e.g., from flashlamp-pumped solid state lasers, such as the ruby laser. Interestingly, whereas the term "solid-state" was extremely apt in differentiating 1950s-era semiconductor electronics from earlier generations of vacuum electronics, it would not have been adequate to convey unambiguously the unique characteristics defining 1960s-era semiconductor lasers.) When an electron and a hole are present in the same region, they may recombine or "annihilate" with the result being spontaneous emission — i.e., the electron may re-occupy the energy state of the hole, emitting a photon with energy equal to the difference between the electron and hole states involved. (In a conventional semiconductor junction diode, the energy released from the recombination of electrons and holes is carried away as phonons, i.e., lattice vibrations, rather than as photons.) Spontaneous emission gives the laser diode below lasing threshold similar properties to an LED. Spontaneous emission is necessary to initiate laser oscillation, but it is one among several sources of inefficiency once the laser is oscillating. The difference between the photon-emitting semiconductor laser (or LED) and conventional phonon-emitting (non-light-emitting) semiconductor junction diodes lies in the use of a different type of semiconductor, one whose physical and atomic structure confers the possibility for photon emission. These photon-emitting semiconductors are the so-called "direct bandgap" semiconductors. The properties of silicon and germanium, which are single-element semiconductors, have bandgaps that do not align in the way needed to allow photon emission and are not considered "direct." Other materials, the so-called compound semiconductors, have virtually identical crystaline structures as silicon or germanium but use alternating arrangements of two different atomic species in a checkerboard-like pattern to break the symmetry. The transition between the materials in the alternating pattern creates the critical "direct bandgap" property. Gallium arsenide, indium phosphide, gallium antimonide, and gallium nitride are all examples of compound semiconductor materials that can be used to create junction diodes that emit light.
In the absence of stimulated emission (e.g., lasing) conditions, electrons and holes may coexist in proximity to one another, without recombining, for a certain time, termed the "upper-state lifetime" or "recombination time" (about a nanosecond for typical diode laser materials), before they recombine. Then a nearby photon with energy equal to the recombination energy can cause recombination by stimulated emission. This generates another photon of the same frequency, travelling in the same direction, with the same polarization and phase as the first photon. This means that stimulated emission causes gain in an optical wave (of the correct wavelength) in the injection region, and the gain increases as the number of electrons and holes injected across the junction increases. The spontaneous and stimulated emission processes are vastly more efficient in direct bandgap semiconductors than in indirect bandgap semiconductors, thus silicon is not a common material for laser diodes.
CHARACTERISTIC OF LASER DIODE
Having analyzed the circuit in the section: "Laser diode power supply 4", I then proceeded to try out a variety of typical visible laser diodes. For all the undamaged laser diodes that I tested, leaving SBT open resulted in safe feedback regulated operation at Vcc1 = Vcc2 = 7 V. But, depending on the particular sample's photodiode sensitivity, optical output power varied widely.
While testing, I used a regulated power supply with adjustable current limit. The voltage was set at 7 V and the current limit knob was used to ramp up the input to the driver while monitoring laser diode current and/or feedback voltage from the photodiode. This approach may have prevented damage to a laser diode on more than one occasion.
Applications of laser diodes
Laser diodes are numerically the most common type of laser, with 2004 sales of approximately 733 million diode lasers, as compared to 131,000 of other types of lasers.
Laser diodes find wide use in telecommunication as easily modulated and easily coupled light sources for fiber optics communication. They are used in various measuring instruments, eg. rangefinders. Another common use is in barcode readers. Visible lasers, typically red but later also green, are common as laser pointers. Both low and high-power diodes are used extensively in the printing industry both as light sources for scanning (input) of images and for very high-speed and high-resolution printing plate (output) manufacturing. Infrared and red laser diodes are common in CD players, CD-ROMs and DVD technology. Violet lasers are used in HD DVD and Blu-ray technology. Diode lasers have also found many applications in laser absorption spectrometry (LAS) for high-speed, low-cost assessment or monitoring of the concentration of various species in gas phase. High-power laser diodes are used in industrial applications such as heat treating, cladding, seam welding and for pumping other lasers, such as diode pumped solid state lasers.
Applications of laser diodes can be categorized in various ways. Most applications could be served by larger solid state lasers or optical parametric oscillators, but the low cost of mass-produced diode lasers makes them essential for mass-market applications. Diode lasers can be used in a great many fields; since light has many different properties (power, wavelength & spectral quality, beam quality, polarization, etc.) it is interesting to classify applications by these basic properties.
Applications of laser diodes can be categorized in various ways. Most applications could be served by larger solid state lasers or optical parametric oscillators, but the low cost of mass-produced diode lasers makes them essential for mass-market applications. Diode lasers can be used in a great many fields; since light has many different properties (power, wavelength & spectral quality, beam quality, polarization, etc.) it is interesting to classify applications by these basic properties.
Medicine and especially Dentistry have found many new applications for diode lasers . The shrinking size of the units and their increasing user friendliness makes them very attractive to clinicians for minor soft tissue procedures. The 800nm - 980nm units have a high absorption rate for hemoglobin and thus make them ideal for soft tissue applications, where good hemostasis is necessary.
Applications which may today or in the future make use of the coherence of diode-laser-generated light include interferometric distance measurement, holography, coherent communications, and coherent control of chemical reactions.
Applications which may make use of "narrow spectral" properties of diode lasers include range-finding, telecommunications, infra-red countermeasures, spectroscopic sensing, generation of radio-frequency or terahertz waves, atomic clock state preparation, quantum key cryptography, frequency doubling and conversion, water purification (in the UV), and photodynamic therapy (where a particular wavelength of light would cause a substance such as porphyrin to become chemically active as an anti-cancer agent only where the tissue is illuminated by light).
Applications where the desired quality of laser diodes is their ability to generate ultra-short pulses of light by the technique known as "mode-locking" include clock distribution for high-performance integrated circuits, high-peak-power sources for laser-induced breakdown spectroscopy sensing, arbitrary waveform generation for radio-frequency waves, photonic sampling for analog-to-digital conversion, and optical code-division-multiple-access systems for secure communication.
3.2.8 OPERATIONAL AMPLIFIER
An operational amplifier, which is often called an op-amp, is a DC-coupled high-gain electronic voltage amplifier with differential inputs and, usually, a single output. Typically the output of the op-amp is controlled either by negative feedback, which largely determines the magnitude of its output voltage gain, or by positive feedback, which facilitates regenerative gain and oscillation. High input impedance at the input terminals (ideally infinite) and low output impedance (ideally zero) are important typical characteristics.
Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents in moderate production volume; however some integrated or hybrid operational amplifiers with special performance specifications may cost over $100 US in small quantities.
The op-amp is one type of differential amplifier. Other types of differential amplifier include the fully differential amplifier (similar to the op-amp, but with 2 outputs), the instrumentation amplifier (usually built from 3 op-amps), the isolation amplifier (similar to the instrumentation amplifier, but which works fine with common-mode voltages that would destroy an ordinary op-amp), and negative feedback amplifier (usually built from 1 or more op-amps and a resistive feedback network).
[pic]
FIG;3.2.9 (IC’S)
3.2.8.1 IDEAL OP-AMP
Shown on the right is an example of an ideal operational amplifier. The main part in an amplifier is the dependent voltage source that increases in relation to the voltage drop across Rin, thus amplifying the voltage difference between V + and V − . Many uses have been found for operational amplifiers and an ideal op-amp seeks to characterize the physical phenomena that make op-amps useful.
[pic]
FIG;3.2.10 (INTERNAL DIAGRAM OF OP AMP)
Supply voltages Vcc + and Vcc − are used internally to implement the dependent voltage sources. The positive source Vs + acts as an upper bound on the output, and the negative source Vs − acts as a lower bound on the output. The internal Vs + and Vs − connections are not shown here and will vary by implementation of the operational amplifier.
Method of application
The amplifier's differential inputs consist of V + input and a V − input, and generally the op-amp amplifies only the difference in voltage between the two. This is called the differential input voltage. Operational amplifiers are usually used with feedback loops where the output of the amplifier would influence one of its inputs. The output voltage and the input voltage it influences settles down to a stable voltage after being connected for some time, when they satisfy the internal circuit of the op amp.
In its most common use, the op-amp's output voltage is controlled by feeding a fraction of the output signal back to the inverting input. This is known as negative feedback. If that fraction is zero (i.e., there is no negative feedback) the amplifier is said to be running open loop and its output is the differential input voltage multiplied by the total gain of the amplifier, as shown by the following equation:
[pic]
where V + is the voltage at the non-inverting terminal, V − is the voltage at the inverting terminal and G is the total open-loop gain of the amplifier.
Since the magnitude of the open-loop gain is typically very large, open-loop operation results in op-amp saturation (see below in Nonlinear imperfections) unless the differential input voltage is extremely small. Finley's law states that "When the inverting and non-inverting inputs of an op-amp are not equal, its output is in saturation." Additionally, the precise magnitude of this gain is not well controlled by the manufacturing process, and so it is impractical to use an operational amplifier as a stand-alone differential amplifier. Instead, op-amps are usually used in negative-feedback configurations.
Most single, dual and quad op-amps available have a standardized pin-out which permits one type to be substituted for another without wiring changes. A specific op-amp may be chosen for its open loop gain, bandwidth, noise performance, input impedance, power consumption, or a compromise between any of these factors.
3.2.9 ELECTROLUMINESCENT WIRE
Electroluminescent wire (often abbreviated to EL wire) is a thin copper wire coated in a phosphor which glows when an AC Current is applied to it. It can be used in a wide variety of applications- vehicle and/or structure decoration, safety and emergency lighting, toys, clothing etc - much as rope light or Christmas lights are often used. Unlike these types of strand lights, EL wire is not a series of points but produces a 360 degree unbroken line of visible light. Its thin diameter makes it flexible and ideal for use in a variety of applications such as clothing or costumes.
Structure
EL wire's construction consists of five major components. First is a solid-copper wire core. This core is coated with phosphor. A very fine wire is spiral-wound around the phosphor-coated copper core. This fine wire is electrically isolated from the copper core. Surrounding this 'sandwich' of copper core, phosphor, and fine copper wire is a clear PVC sleeve.
Finally, surrounding this thin, clear PVC sleeve is a colored translucent PVC sleeve. An electric potential of approximately 90 - 120 volts at about 1000 Hz is applied between the copper core wire and the fine wire that surrounds the phosphor coated copper core. The wire can be modelled as a coaxial capacitor with about 1 nF of capacitance per foot, and the rapid charging and discharging of this capacitor excites the phosphor to emit light.
A resonant oscillator is typically used to generate the high voltage drive signal. Because of the capacitance load of the EL wire, using an inductive (coiled) transformer makes the driver a tuned LC oscillator, and therefore very efficient. The efficiency of EL wire is very high, and thus a few hundred feet of EL wire can be driven by AA batteries for several hours.
[pic]
FIG;3.2.11 (PVC CABLE)
3.2.10 ELECTRONICS\ CAPACITORS
A capacitor (historically known as a "condenser") is a device that stores energy in an electric field, by accumulating an internal imbalance of electric charge. It is made of two conductors separated by a dielectric (insulator). Using the same analogy of water flowing through a pipe, a capacitor can be thought of as a tank, in which the charge can be thought of as a volume of water in the tank. The tank can "charge" and "discharge" in the same manner as a capacitor does to an electric charge. A mechanical analogy is that of a spring. The spring holds a charge when it is pulled back.
When voltage exists one end of the capacitor is getting drained and the other end is getting filled with charge.This is known as charging. Charging creates a charge imbalance between the two plates and creates a reverse voltage that stops the capacitor from charging. As a result, when capacitors are first connected to voltage, charge flows only to stop as the capacitor becomes charged. When a capacitor is charged, current stops flowing and it becomes an open circuit. It is as if the capacitor gained infinite resistance.
You can also think of a capacitor as a fictional battery in series with a fictional resistance. Starting the charging procedure with the capacitor completely discharged, the applied voltage is not counteracted by the fictional battery, because the fictional battery still has zero voltage, and therefore the charging current is at its maximum. As the charging continues, the voltage of the fictional battery increases, and counteracts the applied voltage, so that the charging current decreases as the fictional battery's voltage increases. Finally the fictional battery's voltage equals the applied voltage, so that no current can flow into, nor out of, the capacitor. Just as the capacitor charges it can be discharged. Think of the capacitor being a fictional battery that supplies at first a maximum current to the "load", but as the discharging continues the voltage of the fictional battery keeps decreasing, and therefore the discharge current also decreases. Finally the voltage of the fictional battery is zero, and therefore the discharge current also is then zero.
Capacitance
Just as the capacitor charges it can be discharged. Think of the capacitor being a fictional battery that supplies at first a maximum current to the "load", but as the discharging continues the voltage of the fictional battery keeps decreasing, and therefore the discharge current also decreases. Finally the voltage of the fictional battery is zero, and therefore the discharge current also is then zero.
C=Q/V eqn (3.7)
Where C is the capacitance in farads, V is the potential in volts, and Q is the charge measured in coulombs. Solving this equation for the potential gives:
V=Q/C eqn (3.8)
The impedance of a capacitor at any given angular frequency is given by:
[pic] eqn (3.9)
where j is [pic], ω is the angular frequency and C is the capacitance.
The charge in the capacitor at any given time is the accumulation of all of the current which has flowed through the capacitor. Therefore, the potential as a function of time can be written as:
[pic] eqn(3.10)
Where i(t) is the current flowing through the capacitor as a function of time.
[pic] eqn(3.11)
This equation is often used in another form. By differentiating with respect to time:
Capacitor Labeling
Capacitors are labelled in several different ways.
Ceramic Disc
Sometimes labeled implicitly, usually labeled with number scheme (223 = 22 000 pF, where 3 represents the number of "0" for instance) The letters "mfd" are often used in place of "µF".
Ceramic Dipped
These usually use the number code. In the above example, the smallest one says "104". This means 10 0000 pF = 100,000 pF. M is a tolerance. The middle one is labeled 393. This means 39 000 pF. The last is 223, meaning 22 000 pF. K is the tolerance. It also has a 100 V working voltage labeled.
Resin-potted mylar/polyester
These are usually labeled explicitly, as there is lots of surface area to write on. This one is 4700 pF, 250 V, 5 kV test. The frequency f0 = 21 MHz is the frequency at which it stops behaving like a capacitor, and more like an inductor.
Electrolytic
Usually electrolytic caps are labeled explicitly, making identification easy.Electrolytics are available in axial and radial-leaded packages. In axial-leaded parts, the negative terminal is indicated by a minus sign printed on the package, or by a shorter lead.
Radial-lead parts often uses color code like resistors. The polarity is usually indicated by arrows on a stripe pointing to the negative terminal.
Tantalum
Tantalum capacitors have high capacitance and low ESR, but low operating voltages. When tantalum capacitors fail, it tends to be "spectacular," they essentially blow up.
Construction
The capacitance of a parallel-plate capacitor constructed of two identical plane electrodes of area A at constant spacing D is approximately equal to the following:
[pic] eqn(3.12)
where C is the capacitance in farads, ε0 is the Permittivity of Space, εr is the Dielectric Constant, A is the area of the capacitor plates, and D is the distance between them.
A dielectric is the material between the two charged objects. Dielectrics are insulators. They impede the flow of charge in normal operation. Sometimes, when a too large voltage has been reached, charge starts flowing. This is called dielectric breakdown and destroys the capacitor. Beginners sometimes misunderstand this. Timing circuits do measure the rate at which a capacitor charges, but they measure a threshold voltage instead of allowing the voltage to build up until dielectric breakdown. (A device which does function this way is a spark gap.)
No charge should ever flow from one plate to the other. Although a current does flow through the capacitor, charges are not actually moving from one plate to the other. As charges are added to one plate, their electric field displaces like charges off of the other plate. This is called a displacement current.
3.2.11 SWITCH
In electronics, a switch is an electrical component which can break an electrical circuit, interrupting the current or diverting it from one conductor to another.The most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts. Each set of contacts can be in one of two states: either 'closed' meaning the contacts are touching and electricity can flow between them, or 'open', meaning the contacts are separated and nonconducting.
Since the advent of digital logic in the 1950s, the term has spread to a variety of digital active devices such as transistors and logic gates whose function is to change their output state between two logic levels or connect different signal lines, and even computers, network switches, whose function is to provide connections between different ports in a computer network.[3] The term 'switched' is also applied to telecommunications networks, and signifies a network that is circuit switched, providing dedicated circuits for communication between end nodes, such as the public switched telephone network. The common feature of all these usages is they refer to devices that control a binary state: they are either on or off, closed or open, connected or not connected.
3.2.11.1 Biased switches
A biased switch is one containing a spring that returns the actuator to a certain position. The "on-off" notation can be modified by placing parentheses around all positions other than the resting position. For example, an (on)-off-(on) switch can be switched on by moving the actuator in either direction away from the centre, but returns to the central off position when the actuator is released.
The momentary push-button switch is a type of biased switch. The most common type is a push-to-make switch, which makes contact when the button is pressed and breaks when the button is released. A push-to-break switch, on the other hand, breaks contact when the button is pressed and makes contact when it is released. An example of a push-to-break switch is a button used to release a door held open by an electromagnet. Changeover push button switches do exist but are even less common.
3.2.11.2 Special types
Switches can be designed to respond to any type of mechanical stimulus: for example, vibration (the trembler switch), tilt, air pressure, fluid level (the float switch), the turning of a key (key switch), linear or rotary movement (the limit switch or microswitch), or presence of a magnetic field (the reed switch).
3.2.11.3 Mercury tilt switch
The mercury switch consists of a drop of mercury inside a glass bulb with 2 contacts. The two contacts pass through the glass, and are connected by the mercury when the bulb is tilted to make the mercury roll on to them.
This type of switch performs much better than the ball tilt switch, as the liquid metal connection is unaffected by dirt, debris and oxidation, it wets the contacts ensuring a very low resistance bounce free connection, and movement and vibration do not produce a poor contact.These types can be used for precision works
1. Knife switch
2. Intermediate switch
OFF[pic]
ON[pic]
FIG ;3.2.12
3. Power switching
When a switch is designed to switch significant power, the transitional state of the switch as well as the ability to stand continuous operating currents must be considered. When a switch is in the on state its resistance is near zero and very little power is dropped in the contacts; when a switch is in the off state its resistance is extremely high and even less power is dropped in the contacts. However when the switch is flicked the resistance must pass through a state where briefly a quarter (or worse if the load is not purely resistive) of the load's rated power is dropped in the switch.
Power switches usually come in two types. A momentary on-off switch (such as on a laser pointer) usually takes the form of a button and only closes the circuit when the button is depressed. A regular on-off switch (such as on a flashlight) has a constant on-off feature. Dual-action switches incorporate both of these features.
3.2.12 THERMISTOR
A thermistor is a type of resistor whose resistance varies with temperature. The word is a portmanteau of thermal and resistor. Thermistors are widely used as inrush current limiters, temperature sensors, self-resetting overcurrent protectors, and self-regulating heating elements.
Thermistors differ from resistance temperature detectors (RTD) in that the material used in a thermistor is generally a ceramic or polymer, while RTDs use pure metals. The temperature response is also different; RTDs are useful over larger temperature ranges, while thermistors typically achieve a higher precision within a limited temperature range.
Basic operation
Assuming, as a first-order approximation, that the relationship between resistance and temperature is linear, then:
ΔR = Kδt eqn(3.13)
ΔR = change in resistance
ΔT = change in temperature
k = first-order temperature coefficient of resistance
Thermistors can be classified into two types depending on the sign of k. If k is positive, the resistance increases with increasing temperature, and the device is called a positive temperature coefficient (PTC) thermistor, or posistor. If k is negative, the resistance decreases with increasing temperature, and the device is called a negative temperature coefficient (NTC) thermistor. Resistors that are not thermistors are designed to have a k as close to zero as possible, so that their resistance remains nearly constant over a wide temperature range.
[pic]
FIG : 3.2.14 (THYRISTOR SYMBOL)
3.2.13 IC 7805
The 78xx (also sometimes known as LM78xx) series of devices is a family of self-contained fixed linear voltage regulator integrated circuits. The 78xx family is a very popular choice for many electronic circuits which require a regulated power supply, due to their ease of use and relative cheapness. When specifying individual ICs within this family, the xx is replaced with a two-digit number, which indicates the output voltage the particular device is designed to provide (for example, the 7805 has a 5 volt output, while the 7812 produces 12 volts). The 78xx line are positive voltage regulators, meaning that they are designed to produce a voltage that is positive relative to a common ground. There is a related line of 79xx devices which are complementary negative voltage regulators. 78xx and 79xx ICs can be used in combination to provide both positive and negative supply voltages in the same circuit, if necessary.
78xx ICs have three terminals and are most commonly found in the TO220 form factor, although smaller surface-mount and larger TO3 packages are also available from some manufacturers. These devices typically support an input voltage which can be anywhere from a couple of volts over the intended output voltage, up to a maximum of 35 or 40 volts, and can typically provide up to around 1 or 1.5 amps of current (though smaller or larger packages may have a lower or higher current rating).
[pic]
FIG;3.15(IC 7805)
Advantages
The 78xx series has several key advantages over many other voltage regulator circuits which have resulted in its popularity:
• 78xx series ICs do not require any additional components to provide a constant, regulated source of power, making them easy to use, as well as economical, and also efficient uses of circuit board real estate. By contrast, most other voltage regulators require several additional components to set the output voltage level, or to assist in the regulation process. Some other designs (such as a switching power supply) can require not only a large number of components but also substantial engineering expertise to implement correctly as well.
• 78xx series ICs have built-in protection against a circuit drawing too much power. They also have protection against overheating and short-circuits, rendering them "essentially indestructible" under most circumstances. In some cases, the current-limiting features of the 78xx devices can provide protection not only for the 78xx itself, but also for other parts of the circuit it is used in, preventing other components from being damaged as well.
Disadvantages
The 78xx devices have a few drawbacks which can make them unsuitable or less desirable for some applications:
• The input voltage must always be higher than the output voltage by some minimum amount (typically 2 volts). This can make these devices unsuitable for powering some devices from certain types of power sources (for example, powering a circuit which requires 5 volts using 6-volt batteries will not work using a 7805).
• As they are based on a linear regulator design, the input current required is always the same as the output current. As the input voltage must always be higher than the output voltage, this means that the total power (voltage multiplied by current) going into the 78xx will be more than the output power provided. The extra input power is dissipated as heat. This means both that for some applications an adequate heatsink must be provided, and also that a (often substantial) portion of the input power is wasted during the process, rendering them less efficient than some other types of power supplies. When the input voltage is significantly higher than the regulated output voltage (for example, powering a 7805 using a 24 volt power source), this inefficiency can be a significant issue.
• Even in larger packages, 78xx integrated circuits cannot supply as much power as many designs which use discrete components, and therefore are generally not appropriate for applications which require more than a few amps of current.
Individual Devices in the Series
There are several common configurations for 78xx ICs, including 7805 (5 volt), 7806 (6 volt), 7808 (8 volt), 7809 (9 volt), 7810 (10 volt), 7812 (12 volt), 7815 (15 volt), 7818 (18 volt), and 7824 (24 volt) versions. The 7805 is very commonly used, as its regulated 5 volt supply can provide an easy and useful power source for most TTL components.
Some manufacturers also produce less common variations on the 78xx design, including lower-power versions such as the LM78Mxx series (500mA) and LM78Lxx series (100mA) from National Semiconductor. Some devices also provide slightly different voltages than usual, such as the LM78L62 (6.2 volts) and LM78L82 (8.2 volts).
Unrelated Devices
Despite similar names, it should be noted that the LM78S40 device from National Semiconductor is not part of the usual 78xx family, and does not use the same design. It is intended to be used as a component in switching regulator designs, and is not a linear regulator like other 78xx devices. Likewise, the 7803SR from Datel is actually a full switching power supply module (designed as a drop-in replacement for 78xx chips), and not actually a linear regulator like the 78xx ICs.
13 MICRO SWITCH
A micro switch is a generic term used to refer to an electric switch that is able to be actuated by very little physical force. They are very common due to their low cost and extreme durability, typically greater than 1 million cycles and up to 10 million cycles for heavy duty models. This durability is a natural consequence of the design. Internally a stiff metal strip must be bent to activate the switch. This produces a very distinctive clicking sound and a very crisp feel. When pressure is removed the metal strip springs back to its original state. Common applications of micro switches include computer mouse buttons and arcade game joysticks and buttons. Micro switches are commonly used in tamper switches on gate valves on fire sprinkler systems and other water pipe systems, where it is necessary to know if a valve has been opened or shut. They have also been used as anti-handling devices in boobytrapped improvised explosive devices manufactured by paramilitary groups e.g. the Provisional IRA during The Troubles.
The defining feature of micro switches is that a relatively small movement at the actuator button produces a relative large movement at the electrical contacts, which occurs at high speed (regardless of the speed of actuation). Most successful designs also exhibit hysteresis, meaning that a small reversal of the actuator is insufficient to reverse the contacts; there must be a significant movement in the opposite direction. Both of these characteristics help to achieve a clean and reliable interruption to the switched circuit.
The first micro switch was invented by Peter McGall in 1932 in Freeport, Illinois. McGall was an employee of the Burgess Battery Company at the time. In 1937 he started the company MICRO SWITCH, which still exists as of 2009. It is now owned by Honeywell Sensing and Control.
The microswitch, which is used to control, regulation, precision engineering, devices, and cars, is an electrical switch that is designed to be operated by the physical movement of mechanical devices, it's usually placement in small spaces. The principal characteristics of the standard microswitches are that it usually works with currents from 0.1A to 15A, it resists temperatures between -30 and 80 Celsius degrees. Nowadays exists a wide range of microswitches for specific applications like level sensors or waterproof switches.
[pic]
FIG;3.16 (SWITCH)
3.2.15 MICROPHONE
A microphone, sometimes referred to as a mike (pronounced /ˈmaɪk/) or—more recently—mic, is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. Microphones are used in many applications such as telephones, tape recorders, hearing aids, motion picture production, live and recorded audio engineering, in radio and television broadcasting and in computers for recording voice, VoIP, and for non-acoustic purposes such as ultrasonic checking.
The most common design today uses a thin membrane which vibrates in response to sound pressure. This movement is subsequently translated into an electrical signal. Most microphones in use today for audio use electromagnetic induction (dynamic microphone), capacitance change (condenser microphone, pictured right), piezoelectric generation, or light modulation to produce the signal from mechanical vibration.
[pic]
FIG;3.2.17 (CONDENSER MICROPHONE)
3.2.15.1 CARBON MICROPHONES
A carbon microphone, formerly used in telephone handsets, is a capsule containing carbon granules pressed between two metal plates. A voltage is applied across the metal plates, causing a small current to flow through the carbon. One of the plates, the diaphragm, vibrates in sympathy with incident sound waves, applying a varying pressure to the carbon. The changing pressure deforms the granules, causing the contact area between each pair of adjacent granules to change, and this causes the electrical resistance of the mass of granules to change. The changes in resistance cause a corresponding change in the voltage across the two plates, and hence in the current flowing through the microphone, producing the electrical signal. Carbon microphones were once commonly used in telephones; they have extremely low-quality sound reproduction and a very limited frequency response range, but are very robust devices.
Unlike other microphone types, the carbon microphone can also be used as a type of amplifier, using a small amount of sound energy to produce a larger amount of electrical energy. Carbon microphones found use as early telephone repeaters, making long distance phone calls possible in the era before vacuum tubes. These repeaters worked by mechanically coupling a magnetic telephone receiver to a carbon microphone: the faint signal from the receiver was transferred to the microphone, with a resulting stronger electrical signal to send down the line. (One illustration of this amplifier effect was the oscillation caused by feedback, resulting in an audible squeal from the old "candlestick" telephone if its earphone was placed near the carbon microphone.
3.2.15.2 PIEZO ELECTRIC MICROPHONES
A crystal microphone uses the phenomenon of piezoelectricity—the ability of some materials to produce a voltage when subjected to pressure—to convert vibrations into an electrical signal. An example of this is Rochelle salt (potassium sodium tartrate), which is a piezoelectric crystal that works as a transducer, both as a microphone and as a slimline loudspeaker component. Crystal microphones were once commonly supplied with vacuum tube (valve) equipment, such as domestic tape recorders. Their high output impedance matched the high input impedance (typically about 10 megohms) of the vacuum tube input stage well. They were difficult to match to early transistor equipment, and were quickly supplanted by dynamic microphones for a time, and later small electret condenser devices. The high impedance of the crystal microphone made it very susceptible to handling noise, both from the microphone itself and from the connecting cable. Piezo transducers are often used as contact microphones to amplify sound from acoustic musical instruments, to sense drum hits, for triggering electronic samples, and to record sound in challenging environments, such as underwater under high pressure. Saddle-mounted pickups on acoustic guitars are generally piezos that contact the strings passing over the saddle. This type of microphone is different from magnetic coil pickups commonly visible on typical electric guitars, which use magnetic induction rather than mechanical coupling to pick up vibration.
3.2.15.3 LASER MICROPHONE
Laser microphones are often portrayed in movies as spy gadgets. A laser beam is aimed at the surface of a window or other plane surface that is affected by sound. The slight vibrations of this surface displace the returned beam, causing it to trace the sound wave. The vibrating laser spot is then converted back to sound. In a more robust and expensive implementation, the returned light is split and fed to an interferometer, which detects frequency changes due to the Doppler effect. The former implementation is a tabletop experiment; the latter requires an extremely stable laser and precise optics.
3.2.16 LOUD SPEAKER
A loudspeaker is an electroacoustical transducer that converts an electrical signal to sound. The term loudspeaker can refer to individual transducers (known as drivers), or to complete systems consisting of an enclosure incorporating one or more drivers and electrical filter components. Loudspeakers (and other electroacoustic transducers) are the most variable elements in a modern audio system and are usually responsible for most audible differences when comparing systems.
[pic]
FIG3.2.18( LOUDSPEAKER)
To adequately reproduce a wide range of frequencies, most loudspeaker systems require more than one driver, particularly for high sound pressure level or high accuracy. Individual drivers are used to reproduce different frequency ranges. The drivers are named subwoofers (very low frequencies), woofers (low frequencies), mid-range speakers (middle frequencies), tweeters (high frequencies) and sometimes supertweeters optimized for the highest audible frequencies.
The terms for different speaker drivers differ depending on the application. In 2-way loudspeakers, there is no "mid-range" driver, so the task of reproducing the midrange sounds falls upon the woofer and tweeter. Home stereos use the designation "tweeter" for high frequencies whereas professional audio systems for concerts may designate high frequency drivers as "HF" or "highs" or "horns".
When multiple drivers are used in a system, a "filter network", called a crossover, separates the incoming signal into different frequency ranges, and routes them to the appropriate driver.
A loudspeaker system with n separate frequency bands is described as "n-way speakers": a 2-way system will have woofer and tweeter speakers; a 3-way system is either a combination of woofer, mid-range and tweeter or subwoofer, woofer and tweeter.
CHAPTER-4
BASIC PROJECT CONSTRUCTION &TESTING
The major blocks of our system are as follows:-
4.1 HARDWARE
A description of the hardware and circuitry used in this project follows. Resistor, capacitor and diode values are ommitted because they need to tuned depending on the hardware used. The specific use for each component is documented.
[pic]
FIG; 4.1 : Microphone Amplifier
The first step in transmitting sound is to digitize soundwaves. For this we used an electret microphone purchased from Radtronics. Frequent shoppers at Tito's place downtown know that finding spec sheets for products there is impossible. The microphone he sold us had three leads, which after considerable angst we decided were for power, ground, and signal. The signal coming off the mic was far too low to be read (with any degree of precision) by the analog to digital converter. So of course, an amplifier is needed. Before the signal is put through the amplifier however it is first put through a capicitor to remove DC, and then through a voltage divider to appropriately bias the signal. A LF353 op-amp is used to boost the signal, the gain is adjusted by the resistors and for the mystery microphone the gain is around 50-100 (depending on how much popping and how much quality you want).
[pic]
FIG; 4.2: Laser Driver
After the A/D converter translates the mic signal into 8 bits, the MCU generates the appropriate bits to send (including start and stop bits) and applies them to the laser driver circuit a 5V and 0V signals. The BJT in this circuit turns on at 5V and provides the proper current according to the diode and resitor values.
[pic]
FIG; 4.3 : Receiver
A photo diode detects the laser pulses in a different (distant) location. This signal is put through a comparator in order to generate solid 5V and 0V values which are applied to the receive pin on the microcontroller.
[pic]
FIG; 4.4: Laser Driver
Once the signal is put through the DAC (not shown, it's a simple ladder), it is boosted and low pass filtered (to improve sound quality).
1) Power Supply: - We will need a +5V/500mA power supply for our project. For this purpose we will use a step down transformer to convert 220VAC/50Hz into 12VAC. The out of transformer is rectified through bridge rectifier using diode 1N4001. Linear voltage regulator IC LM7805 is used to provide a stable regulated +5V supply for microcontroller and other parts in the project.
2) LED: - In our project we will be using a LED for displaying the LASER COMMUNICATION.
3) LASER DIODE : - In our project we will use LASER DIODE for sensing effect of LASER communication . These LASER DIODE basically used for LASER LIGHT which is required for LASER COMMUNICATION.
4) AMPLIFIER & FILTER: - The function of electronics amplifier & filter is to amplify the weak signal received by electrodes without noise. The amplification and filtering is done in multiple stage.
[pic] FIG; 4.5: CIRCUIT DIAGRAM OF LASER COMMUNICATION SYSTEM
5) Transmitter
A laser diode needs a certain value of current, called the threshold current, before it emits laser light. A further increase in this current produces a greater light output. The relationship between output power and current in a laser diode is very linear, once the current is above the threshold, giving a low distortion when the beam is amplitude modulated. For example, the 65Onm 5mW laser diode used in this project has a typical threshold current of 3OmA and produces its full output when the current is raised by approximately 1OmA above the threshold to 4OmA. Further increasing the current will greatly reduce the life of the laser diode, and exceeding the absolute maximum of 8OmA will destroy it instantly. Laser diodes are very fragile and will not survive electrostatic discharges and momentary surges!
However, if used within specifications, the typical life of one of these lasers is around 20,000 hours. In the transmitter circuit the laser diode is supplied via an adjustable constant-current source. Since the lasing threshold also varies with temperature, a 68ohm NTC thermistor is included to compensate for changes in ambient temperature. Note that the metal housing for the laser diode and the lens also acts as a heatsink. The laser diode should not be powered without the metal housing in place. The quiescent laser diode current is controlled by Q2, in turn driven by the buffer stage of 1C2b. The DC voltage as set by VR2 appears at the base of Q2, which determines the current through the transistor and therefore the laser diode. Increasing the voltage at VR1 reduces the laser current. The setting of VR1 determines the quiescent brightness of the laser beam, and therefore the overall sensitivity of the system.
The audio modulation voltage is applied to the cathode of the laser diode, which varies the laser current around its set point by around +/-3mA. The modu- lation voltage is from the emitter of Q 1, which is an emitter follower stage driven by the audio amplifier stage of 1C2a. Diodes D4 to D7 limit the modulating voltage to +/-2V, while C4 and C5 block the DC voltages at the emitter of Q 1 and the cathode of the laser diode. The audio signal is coupled to the laser diode via R10, which limits the maximum possible variation in the laser diode current to a few milliamps.
LED1 gives an indication of the modulating voltage. Diodes D2, D3 and resistor R8 limit the current through the LED and enhance the brightness changes so the modulation is obvious. The LED flickers in sympathy with the sound received by the microphone, giving an indication that a modulating volt- age is present.
The inverting amplifier of 1C2a includes a form of compression, in which the output level is relatively constant and independent of how soft or loud the audio level is at the microphone. This is achieved by FET Q3 and its associated circuitry.
The cascaded voltage doubler of C9, D8, D9 and C8 rectifies the audio signal at the emitter of Ql, and the resulting negative DC voltage is fed to the gate of Q3. An increase in the audio signal will increase the negative bias to Q3, increasing its drain-source resistance. Because the gain of 1C2a is determined by R7 and the series resistance of R5 and Q3, increasing the effective resistance of Q3 will lower the gain.
Since the compression circuit takes time to respond, the clamping network of D4-D7 is still needed to protect against sudden voltage increases. This system is rather similar to the compression used in portable tape recorders.
The electret microphone is powered through R1 and is coupled to the non inverting input of 1C2a via C6. This input is held at a fixed DC voltage to give a DC output to bias Ql.
The supply voltage to the transmitter circuit is regulated by ICI, a 5V three terminal regulator.
6) Transmitter
A laser diode needs a certain value of current, called the threshold current, before it emits laser light. A further increase in this current produces a greater light output. The relationship between output power and current in a laser diode is very linear, once the current is above the threshold, giving a low distortion when the beam is amplitude modulated. For example, the 65Onm 5mW laser diode used in this project has a typical threshold current of 3OmA and produces its full output when the current is raised by approximately 1OmA above the threshold to 4OmA. Further increasing the current will greatly reduce the life of the laser diode, and exceeding the absolute maximum of 8OmA will destroy it instantly. Laser diodes are very fragile and will not survive electrostatic discharges and momentary surges!
However, if used within specifications, the typical life of one of these lasers is around 20,000 hours. In the transmitter circuit the laser diode is supplied via an adjustable constant-current source. Since the lasing threshold also varies with temperature, a 68ohm NTC thermistor is included to compensate for changes in ambient temperature. Note that the metal housing for the laser diode and the lens also acts as a heatsink. The laser diode should not be powered without the metal housing in place. The quiescent laser diode current is controlled by Q2, in turn driven by the buffer stage of 1C2b. The DC voltage as set by VR2 appears at the base of Q2, which determines the current through the transistor and therefore the laser diode. Increasing the voltage at VR1 reduces the laser current. The setting of VR1 determines the quiescent brightness of the laser beam, and therefore the overall sensitivity of the system.
The audio modulation voltage is applied to the cathode of the laser diode, which varies the laser current around its set point by around +/-3mA. The modu- lation voltage is from the emitter of Q 1, which is an emitter follower stage driven by the audio amplifier stage of 1C2a. Diodes D4 to D7 limit the modulating voltage to +/-2V, while C4 and C5 block the DC voltages at the emitter of Q 1 and the cathode of the laser diode. The audio signal is coupled to the laser diode via R10, which limits the maximum possible variation in the laser diode current to a few milliamps.
LED1 gives an indication of the modulating voltage. Diodes D2, D3 and resistor R8 limit the current through the LED and enhance the brightness changes so the modulation is obvious. The LED flickers in sympathy with the sound received by the microphone, giving an indication that a modulating volt- age is present.
The inverting amplifier of 1C2a includes a form of compression, in which the output level is relatively constant and independent of how soft or loud the audio level is at the microphone. This is achieved by FET Q3 and its associated circuitry.
The cascaded voltage doubler of C9, D8, D9 and C8 rectifies the audio signal at the emitter of Ql, and the resulting negative DC voltage is fed to the gate of Q3. An increase in the audio signal will increase the negative bias to Q3, increasing its drain-source resistance. Because the gain of 1C2a is determined by R7 and the series resistance of R5 and Q3, increasing the effective resistance of Q3 will lower thegain.
Since the compression circuit takes time to respond, the clamping network of D4-D7 is still needed to protect against sudden voltage increases. This system is rather similar to the compression used in portable tape recorders.
The electret microphone is powered through R1 and is coupled to the non inverting input of 1C2a via C6. This input is held at a fixed DC voltage to give a DC output to bias Ql.
The supply voltage to the transmitter circuit is regulated by ICI, a 5V three terminal regulator.
Receiver
The transmitted signal is picked up by the photo detector diode in the receiver. The output voltage of this diode is amplified by the common emitter amplifier around Ql. This amplifier has a gain of 20 or so, and connects via VRI to ICI, an LM386 basic power amplifier IC with a gain internally set to 20.
This IC can drive a speaker with a resistance as low as four ohms, and 35OmW when the circuit is powered from a 9V supply. Increasing the sup- ply voltage will increase the output power marginally.
The voltage to the transistor amplifier stage is regulated by ZD I to 5.6V, and decoupled from the main supply by R2 and C2. Resistor R3 supplies forward current for the photodiode. (Incidentally, the photodiode used for this project has a special clear package, so it responds to visible light, and not just infrared.)
4.2 CONSTRUCTION
As the photos show, both the transmitter and the receiver are built on silk- screened PCBS. As usual fit the resistors, pots and capacitors first, taking care with the polarity of the electrolytics. IC sockets are not essential, although servicing is obviously made easier if they are used. In which case, fit these next, followed by the transistors, diodes and the LED.
Take care to use the right diodes for D8 and D9. These are larger than the 1N4148 types, and have two black bands (the cathode end) around a glass package. Note that the regulator IC has the tab facing outwards.
The photodiode is mounted directly on the receiver PCB. When first mounted, the active side of the diode (black square inside the package) will face towards the centre of the board. You then bend the diode over by almost 180' so the active surface now faces outwards.
The polarised microphone element solders directly to the transmitter PCB. The negative lead is marked with a minus sign and is the lead that connects to the metal case.
The laser diode is also polarised, and has three leads. Of these, only two are used, shown on the circuit as pins 2 (cathode) and 3 (anode). Take care when soldering the laser in place, as too much heat can destroy it. The diode can be mounted on the board, or connected with leads to it.
Finally, connect the speaker and 9V battery clips, then check over the boards for any soldering errors or incorrectly installed components.
23 TESTING
First of all, it's most important that you don't look directly into the laser beam. If you do, it could cause perma- nent eye damage. Also, you are respon- sible for the safety of others near the laser, which means you must stop others from also looking into the beam, and take all necessary safety steps. This is covered by legislation.
Both the receiver and the transmitter can be powered by separate 9V batteries or suitable DC supplies. Before apply- ing power to the transmitter PCB, set VRI to its halfway position, to make sure the laser current is not excessive. To be totally sure, you could set VRI fully anticlockwise, as this setting will reduce the laser current to zero.
Then apply power to the board. If the laser doesn't produce light, slowly adjust VRI clockwise. The laser diode should emit a beam with an intensity adjustable with VRI. At this stage, keep the beam intensity low, but high enough to clearly see. If you are not getting an output, check the circuit around IC2b.
You should also find that LED 1 flickers if you run your finger over the microphone. If so, it indicates that the amplifier section is working and that there's a modulation voltage to the laser diode. You won't see the laser beam intensity change with the modu- lating signal.
To check that the system is working, place the two PCBs on the workbench, spaced a metre or go apart. You might need to put a sheet of paper about 2Omm in front of the photodiode to reduce the intensity of light from the laser beam. Set the volume control of the speaker to about halfway. If the volume control setting is too high you'll get acoustic feedback.
Move the laser diode assembly so the beam points at the receiver's photodi- ode. It's useful to adjust the beam so it's out of focus at the photodiode, to make alignment even easier. You should now be able to hear the speaker reproducing any audio signal picked up by the microphone. When the receiver and transmitter are in close range, the strength of the beam can cause the receiver to respond even if the laser beam is not falling on the photodiode.
4.3.1SETTINGUPLINK
Once you've tested the link, you'll probably be keen to put it to use. For a short link of say 100 metres, all you need do is position the receiver so the laser beam falls on the photodiode. Once the link is established, adjust VRI higher the laser current, the shorter will be its life.
If you have an ammeter, connect it to measure the current taken by the trans- mitter board. Most of the current is taken by the laser, so adjust VRI to give a total current consumption of no more than 45mA.
Also, focus the laser so all of the beam is striking the photodiode. At close range, there's probably no need to focus the beam. In fact, because of the high output power (5mW) of the laser diode, excellent results will be obtained over reasonably short distances (20 metres or so) with rough focusing and quiescent current adjust- ments. But the longer the dis- tance between the transmitter and the receiver, the more critical the adjustments. For example, for distances over 20 metres, you might have to put a piece of tube over the front of the photodi- ode to limit the ambient light falling on it. This diode is responsive to visible light, so a high ambient light could cause it to saturate. For very long distances, say a kilome- tre, you'll probably need a parabolic reflector for the laser beam, to focus it direct- ly onto the photodiode.
For short ranges (a metre or so), or for educational or testing purposes, you can use a conventional red LED. Adjust the quiescent current with VR1. The light output of a LED is not focused, and simply spreads everywhere, so a reflector might help the sensitivity. Warnings The laser diode in this project is a class 3B laser and you should attach a warning label to the trans- mitter. Labels will be sup- plied by Oatley Electronics. Remember that, as for any hazardous device, the owner of a laser is responsible for its proper use. Receiver
The transmitted signal is picked up by the photo detector diode in the receiver . The output voltage of this diode is amplified by the common emitter amplifier around Ql. This amplifier has a gain of 20 or so, and connects via VRI to ICI, an LM386 basic power amplifier IC with a gain internally set to 20.
This IC can drive a speaker with a resistance as low as four ohms, and 35OmW when the circuit is powered from a 9V supply. Increasing the sup- ply voltage will increase the output power marginally.
The voltage to the transistor amplifier stage is regulated by ZD I to 5.6V, and decoupled from the main supply by R2 and C2. Resistor R3 supplies forward current for the photodiode. (Incidentally, the photodiode used for this project has a special clear package, so it responds to visible light, and not just infrared.)
HARDWARE REQUIREMENTS
• PCB
• STEP DOWN TRANSFORMER 5V/500mA
• VOLTAGE REGULATOR LM7805
• RECTIFIER DIODES 1N4001
• ELECTROLYTIC CAPACITORS
• LED DISPLAY
• LEDs
• IC 7447, 8870, 91214.
• Tr. BC-548
• Laser diode
• OPERATIONAL AMPLIFIER
• PVC WIRES
• RESSISTANCE 10K
• CAPACITOR 104PF
• DPDT S/W
• IC 7805
• MICRO SWITCH
• CRYSTAL 12 MHZ
• RESET 100K
• MIKE
• SPEAKER 5 OHM
CHAPTER-5
SAFETY & PRECAUTIONS FOR LASER SYSTEMS
5.1 SAFTEY
Laser safety is the avoidance of laser accidents, especially those involving eye injuries. Since even relatively small amounts of laser light can lead to permanent eye injuries, the sale and usage of lasers is typically subject to government regulations.
Moderate and high-power lasers are potentially hazardous because they can burn the retina of the eye, or even the skin. To control the risk of injury, various specifications, for example ANSI Z136 in the US and IEC 60825 internationally, define "classes" of laser depending on their power and wavelength. These regulations also prescribe required safety measures, such as labeling lasers with specific warnings, and wearing laser safety goggles when operating lasers.
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5.1.1 LASER RADIATION HAZARDS
Laser radiation predominantly causes injury via thermal effects. Even moderately powered lasers can cause injury to the eye. High power lasers can also burn the skin. Some lasers are so powerful that even the diffuse reflection from a surface can be hazardous to the eye.
The coherence, the low divergence angle of laser light and the focusing mechanism of the eye means that laser light can be concentrated into an extremely small spot on the retina. A transient increase of only 10 °C can destroy retinal photoreceptors. If the laser is sufficiently powerful, permanent damage can occur within a fraction of a second, faster than the blink of an eye. Sufficiently powerful visible to near infrared laser radiation (400-1400 nm) will penetrate the eyeball and may cause heating of the retina, whereas exposure to laser radiation with wavelengths less than 400 nm and greater than 1400 nm are largely absorbed by the cornea and lens, leading to the development of cataracts or burn injuries
Infrared lasers are particularly hazardous, since the body's protective "blink reflex" response is triggered only by visible light. For example, some people exposed to high power Nd:YAG laser emitting invisible 1064 nm radiation, may not feel pain or notice immediate damage to their eyesight. A pop or click noise emanating from the eyeball may be the only indication that retinal damage has occurred i.e. the retina was heated to over 100 °C resulting in localized explosive boiling accompanied by the immediate creation of a permanent blind spot.
DAMAGE MECHANISM
Lasers can cause damage in biological tissues, both to the eye and to the skin, due to several mechanism. Thermal damage, or burn, occurs when tissues are heated to the point where denaturation of proteins occurs. Another mechanism is photochemical damage, where light triggers chemical reactions in tissue. Photochemical damage occurs mostly with short-wavelength (blue) and ultra-violet light and can be accumulated over the course of hours. Laser pulses shorter than about 1 μs can cause a rapid raise in temperature, resulting in explosive boiling of water. The shock wave from the explosion can subsequently cause damage relatively far away from the point of impact. Ultrashort pulses can also exhibit self-focusing in the transparent parts of the eye, leading to an increase of the damage potential compared to longer pulses with the same energy.
The eye focuses visible and near-infrared light onto the retina. A laser beam can be focused to an intensity on the retina which may be up to 2×105 times higher than at the point where the laser beam enters the eye. Most of the light is absorbed by melamine pigments in the pigment epithelium just behind the photoreceptor and causes burns in the retina. Ultraviolet light with wavelengths shorter than 400 nm tends to be absorbed in the cornea and lens, where it can produce injuries at relatively low powers due to photochemical damage. Infrared light mainly causes thermal damage to the retina at near-infrared wavelengths and to more frontal parts of the eye at longer wavelengths. The table below summarizes the various medical conditions caused by lasers at different wavelengths, not including injuries due to pulsed lasers.
5.2 MAXIMUM PERMISSIBLE EXPOSURE
The maximum permissible exposure (MPE) is the highest power or energy density (in W/cm2 or J/cm2) of a light source that is considered safe, i.e. that has a negligible probability for creating a damage. It is usually about 10% of the dose that has a 50% chance of creating damage under worst-case conditions. The MPE is measured at the cornea of the human eye or at the skin, for a given wavelength and exposure time.
A calculation of the MPE for occular exposure takes into account the various ways light can act upon the eye. For example, deep-ultraviolet light causes accumulating damage, even at very low powers. Infrared light with a wavelength longer than about 1400 nm is absorbed by the transparent parts of the eye before it reaches the retina, which means that the MPE for these wavelengths is higher than for visible light. In addition to the wavelength and exposure time, the MPE takes into account the spatial distribution of the light (from a laser or otherwise). Collimated laser beams of visible and near-infrared light are especially dangerous at relatively low powers because the lens focuses the light onto a tiny spot on the retina. Light sources with a smaller degree of spatial coherence than a well-collimated laser beam lead to a distribution of the light over a larger area on the retina. For such sources, the MPE is higher than for collimated laser beams. In the MPE calculation, the worst-case scenario is assumed, in which the eye lens focuses the light into the smallest possible spot size on the retina for the particular wavelength and the pupil is fully open. Although the MPE is specified as power or energy per unit surface, it is based on the power or energy that can pass through a fully open pupil (0.39 cm2) for visible and near-infrared wavelengths.
This is relevant for laser beams that have a cross-section smaller than 0.39 cm2. The IEC-60825-1 and ANSI Z136.1 standards include methods of calculating MPEs.
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5.3 LASER SAFTEY IN RESEARCH ENVIORNMENT
It is common in research in both university and industrial laboratories for operators to violate safety regulations and remove their eye protection during certain procedures, or even to avoid wearing it altogether. Some find the use of safety glasses over a long time to be uncomfortable, and in many types of optical experiments it is also inconvenient. For example in spectroscopy, the experimental arrangement is constantly being modified and fine-tuned. This requires knowledge of beam location, which is often most simply achieved with the naked eye, although other, often less accurate, detection methods are available. In this situation, many scientists assign a higher priority to convenience and comfort than to safety and regulatory compliance, and routinely breach the laser safety regulations. Sometimes it is perceived as unavoidable when working with, for example, an RGB laser, which would require very careful selection of the Optical Density of protective eyewear or the use of completely black goggles.
Eye protection is often considered uncomfortable because of both reduced vision and physical discomfort. Especially for goggles that protect against visible-light wavelengths, color vision is impaired, which means that it becomes hard to see green or red indicator lights on equipment and to recognize tools. Moreover, many types of goggles transmit less than 30 percent of visible light which means that standard work environment lighting levels may be inadequate, leading to increased risks for other accidents, such as tripping over cables. Finally, the weight, fit, and ventilation may cause physical discomfort.
When eye protection is neglected, scientists attempt to minimize risks by other means, such as keeping all beams within a restricted horizontal space, and removing jewelry. However, the reduced safety measures commonplace in scientific environments cannot completely prevent accidents. It is not uncommon for someone who did several years of laser-related research to have experienced an accident that resulted in a small, but permanent eye injury, typically a blind spot somewhere in the peripheral vision.
Experimentalists often feel that safety eyewear is not necessary when dealing with an experiment carried out within the horizontal plane. However, in a non-trivial optical setup, it is very hard to ensure that all mirrors, filters, and lenses are strictly kept in a vertical position at all times, particularly when the setup is constantly modified, and that metallic tools such as screwdrivers also can redirect a beam. Stray reflections are usually unnoticed until an accident occurs. Since nobody can guarantee that all these hazards can be safely avoided without wearing safety eyewear, when infrared laser beams with non-negligible powers are used, working without safety eyewear is not permitted by any official safety regulations.
CONCLUSION
Our project has demonstrated a basic system that utilizes a laser beam as the method of communication. As a proof of concept, we have accomplished what we set out to do. The laser communication system can pass data via laser pulses over air, and transmit that data as a byte up to the receiver. The receiver platform then can utilize the data and reconstruct the data sequence that was sent from the transmitter.Because of the versatility in this setup, we could possibly send over a wide range of data, supporting a wide range of networks. Currently, we support data communication and data commands, but this could easily be expanded upon, once a more precise interface is developed. We have also shown that the power consumption of such a network is minimal compared to an RF network. For certain types of wireless networks, a laser based communication structure could possibly make sense.
Much future work still needs to be done however. One optimization would be to improve both the speed and bandwidth of the transmissions. Currently, the speed of transmissionis not fast enough for any industrial application. Possible solutions would be to rework the pulse patterns so that data can be transmitted in fewer pulses.
The laser based system is an easy to use display or grade control system for rough and fine grade work on construction sites, enabling machine operators to get to grade quicker than before. The versatile PA System allows for the system to be configured as an indicate or automatic grade control system and can be easily installed on a wide variety of machines and for different applications.
The system increases job site profitability by getting to grade in fewer passes. This reduces on the job time, and allows for labor and equipment to be used more efficiently. And with improved accuracy, material costs are reduced. All this adds up to improved profitability on each job.
APPENDIX 1 –ACRONYMS
LASER light amplification stimulated emission and radiation
ANSI American national standard institute
ARIB association of radio industries and broadcasting
ACL asynchronous connectionless link
LED light emitting diode
BER bit error rate
PCB printed circuit board
Codec coder decoder
WDM wavelength division multiplexing
EFR enhance full rate
Op-amp operational amplifier
MF medium frequency
IC integrated circuit
DPDT as switch case
TX transmitter
Rx receiver
APPENDIX -2 GLOSSARY
PCB- PCBs are boards whereupon electronic circuits have been etched. PCBs are rugged, inexpensive, and can be highly reliable.
STEP DOWN TRANSFORMER:
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors — the transformer's coils or "windings". INDUCTION LAW --The voltage induced across the secondary coil may be calculated from Faraday's law of induction, which states that:
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Linear regulator
In electronics, a linear regulator is a voltage regulator based on an active device (such as a bipolar junction transistor, field effect transistor or vacuum tube) operating in its "linear region" (in contrast, a switching regulator is based on a transistor forced to act as an on/off switch) or passive devices like zener diodes operated in their breakdown region.
ZENER REGULATOR
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SIMPLE SERIES REGULATOR
Adding an emitter follower stage to the simple zener regulator forms a simple series voltage regulator and substantially improves the regulation of the circuit
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RECTIFIER
A rectifier is an electrical device that converts alternating current (AC) to direct current (DC), a process known as rectification
ELECTROLYTIC CAPACITOR
An electrolytic capacitor is a type of capacitor that uses an ionic conducting liquid as one of its plates with a larger capacitance per unit volume than other types
LIGHT EMITTING DIODE
A light-emitting diode (LED) , is an electronic light source
INTEGRATED CIRCUIT
In electronics, an integrated circuit (also known as IC, microcircuit, microchip, silicon chip, or chip) is a miniaturized electronic circuit (consisting mainly of semiconductor devices
LASER DIODE
A laser diode is a laser where the active medium is a semiconductor similar to that found in a light-emitting diode
OPERATIONAL AMPLIFIER
An operational amplifier, which is often called an op-amp, is a DC-coupled high-gain electronic voltage amplifier with differential inputs and, usually, a single output.
ELECTRONICS\ CAPACITORS
A capacitor (historically known as a "condenser") is a device that stores energy in an electric field, by accumulating an internal imbalance of electric charge
C=Q/V
SWITCH
a switch is an electrical component which can break an electrical circuit, interrupting the current or diverting it from one conductor to another
THERMISTOR
A thermistor is a type of resistor whose resistance varies with temperature
MICRO SWITCH
A micro switch is a generic term used to refer to an electric switch that is able to be actuated by very little physical force
MICROPHONE
A microphone, sometimes referred to as a mike (pronounced /ˈmaɪk/) or—more recently—mic, is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal
LOUD SPEAKER
A loudspeaker is an electroacoustical transducer that converts an electrical signal to sound
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