Design Project



Homework 5: Theory of Operation and Hardware Design Narrative Team Code Name: ____________________________________________ Group No. ______Team Member Completing This Homework: _______________________________________E-mail Address of Team Member: ______________ @ purdue.eduNOTE: This is the second in a series of four “design component” homework assignments, each of which is to be completed by one team member. The body of the report should be 3-5 pages, not including this cover page, references, attachments or appendices.Evaluation:SECDESCRIPTIONMAXSCORE1.0Introduction 5 2.0Theory of Operation203.0Hardware Design Narrative204.0 Summary55.0List of References10App ASystem Block Diagram10App BSchematic30TOTAL =SUM(ABOVE) 100Comments:Comments from the grader will be inserted hereIntroductionBrief description of design project, with a focus on circuit design issues.The Wall-E system contains two major parts: one is the server side PC which does the image processing, and generates commands, the other is the mobile robot platform which collects information via sensors, and executes commands sent from the server PC. These two parts communicates with each other wirelessly. Due to the space constrain of the mobile robot platform, the major circuit design challenge is to incorporate the many electrical components of various purposes, operating modes and voltages on the mobile robot platform tightly together, while keep the noise and heat hazards under control. To achieve this, the major electrical components are grouped onto two different boards. One is the high voltage motor driver board which runs on 12V and contains the mechanical control components, the other is the low voltage custom PCB which runs on 3.3V and contains microcontroller, and other noise sensitive components such as the XBee transceiver.Theory of OperationDescribe the function and operating mode of each major subsection of the circuit, as well as how the subsections relate to each other. Discuss the function and operating mode of major components, including rationale for choice of operating frequency, supply voltage(s), etc, not rationale for the choice of the component. Do not rehash the manufacturers’ data sheets for the parts. Tell us how the parts work in your circuit. The system hardware can be divided into five basic components:The microcontrollerPower supply and voltage modulatorMotor and servo control circuitSensor circuit (Ultrasonic sensor and wireless camera)Wireless control circuitEach component plays a vital role in the system. The wireless control circuit is used for signal transmission between the computer and the microcontroller on the robot. It includes a pair of Xbee Pro. One of the XBee connects to the computer via a USB port. The other one communicates with the microcontroller via UART. The Xbee pair operating at 3.3V which is the same supply voltage of the microcontroller. The sensor circuit helps us obtain the environment parameters around the robot as the input to the whole system. It consists of a wireless camera and four ultrasonic sensors. The wireless camera captures the image in front of the robot and sends it back to the computer. It works at 5V DC which is supply by the 5V voltage regulator on the L298 motor driver board. The 4 ultrasonic sensors operate on their analog output mode (10mV/inch) and transmit the signal to the micro controller through the ATD channels. They share the same supply voltage of 3.3V with the microcontroller so it is directly powered with the 3.3V power supply onboard the PCB. The reading rate for the sensors is 20Hz. The motor and servo control circuit is used for controlling the mechanical parts of the robot. It includes a motor control board, two 12V gear head motors and two 5V TR205 servos. The core component of the motor control board is a L298 H-bridge, which uses 12V DC as its power supply. Two 12V DC output ports are used to supply voltage to the motors, and each of these ports has a maximum current sinking/sourcing capability of 2A. The motor control board has 6 input pins. (Two motor enable pins are connected to two general I/O pins on the microcontroller and four motor direction control pins receives signals from the microcontroller PWM channels). There’s an additional voltage regulator on the motor drive board which provides the user with a 5VDC up to 1A voltage supply. This will be used to drive the two servos on the mechanical arm and the onboard wireless camera. Since all the components are onboard a mobile platform, a 12.0 Volt Ni-MH 2800mAh battery pack is used as the main power supply. With the motors directly powered by the 12V battery pack, and the servos being powered by the regulated 5V output from the motor driver circuit, all the remaining components onboard the PCB run on 3.3V DC. Thus a 12V to 3.3V voltage regulator is used to step down the voltage to supply power to the PCB components, which include a fuel gauge that indicates the battery level, and monitors the charging and discharging cycles of the battery.Hardware Design NarrativeDiscuss which subsystems of the microcontroller will be used and how they will be used. Discuss the port assignments of the microcontroller and why specific ports were chosen for specific functions. Include power, ground, and bypass capacitor considerations. For the other major subsystems, discuss any specific configuration choices and how this effects the interconnection between these subsystems and the microcontroller. Reference the schematic (included as Appendix B) in this discussion.The microcontroller onboard the robot is a 64pin, 16-bit, 256KB memory PIC24FG256GA106, which provides enough peripherals for the robot, while keeping the pin count at minimum. To minimize the communication delay between the PC and the robot, the microcontroller will be clocked at the maximum operating frequency of 32MHz. In the operating voltage range of 2.0V to 3.6V, 3.3V is used to power the microcontroller, which is consistent with other parts onboard the same PCB. This power is directly derived from the output of the 12V to 3.3V voltage convertor, which takes the 12V unregulated battery pack output as input. As recommended by the manufacture, between every pair of Vdd/AVdd and Vss/AVss (Power and Ground), a 0.1uF (100 nF), 10-20V ceramic primary decoupling capacitor is installed. Since the noisy mechanical control circuit is populated on a separate board, the operation onboard this PCB is generally low noise. Therefore, a secondary decoupling capacitor is not needed. For system reset, the active low MCLR pin is connected to a 470KOhm current limiting resistor, which is then connected to a 10KOhm resistor to Vdd, and a push button with a 0.1uF ceramic capacitor to Vss. To provide accurate clock source, different sampling frequency, and transmitting baud rate, a primary and a secondary external oscillator are connected to the OSCO, OSCI, and the SOSCO, SOSCI pins. The clock source for the primary external oscillator and the secondary external oscillator are an 8MHz crystal, and a 32KHz crystal respectively. Among the peripherals available, 4 of the 16 ATD channels are utilized to sample the result from the 4 ultrasonic range sensors. 4 of 9 PWM channels are used to control the speed, direction of the 2 motors, and 2 more PWM channels are used to control the position of the 2 servos on the robotic arm. To communicate through XBee, 1 pair (Tx and Rx) of the 4 pairs of UART ports is set to 9600 baud rate, 8-bit, no polarity. One of the 5 timers is used to count the 90 degree rotating time for the obstacle avoiding algorithm. Besides these designated peripheral pins, 31 pins are remappable, and can be configured as general I/Os, 1 of these I/Os is used to implement the TI HDQ protocol for fuel gauge interfacing, another 2 are connected to the enable pins for each motor on the 12V motor drive board. The schematic included in the Appendix B is a graphical presentation of the description above. As of off-board component interconnection, this PCB will be connected to the main battery pack in parallel with the motor drive board. In other words, the power pack is directly connected to the 12V to 3.3V converter on the PCB, and the 12V power input of the motor drive board. This configuration keeps the two sets of systems (12V/5V electro-mechanical parts and 3.3V electrical control parts) as separated as possible, and ensures a clean power for the more sensitive 3.3V PCB board. This minimizes any negative effect from one to the other (ie. Noise, heat, excessive current, unexpected short), and protects the microcontroller circuits. SummaryBriefly summarize the contents of this report.Before summarizes the utilization of the microcontroller pins and peripherals. This report gives an overview of the project hardware design. These hardware components are then divided into different functional groups for more detailed operation characteristics analysis. With the operation characteristics and functions presented, a layout is developed, and presented in the form of block diagram and schematic, which are included in the Appendix A and B respectively. 5.0 List of ReferencesReference1…Reference2…Reference3…IMPORTANT: Use standard IEEE format for references, and CITE ALL REFERENCES listed in the body of your report. Provide “live” links to all data sheets utilized.Appendix A: System Block DiagramInsert an updated version of your block diagram here. Include the bus widths where applicable and indicate microcontroller ports associated with the signals.Appendix B: SchematicInsert a copy of your schematic here. Split into multiple sheets, as appropriate, making sure that it is readable. ................
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