EE230DesignProject2.docx.docx



Signal Generator – Design Project 2Daniel Borgerding and Charles PattersonSection BApril 22nd 2014IntroductionFor the second design project of the semester our team chose the temperature indicator circuit. This circuit takes the signal from a temperature measurement sensor, in this case we used the LM35 by Texas Instruments, and lights up color coded LED’s based upon the temperature level. The circuit we built behaves differently depending on if the temperature is rising or falling. The requirements for our project were as follows:As the temperature increases:? A green LED will be lit for temperatures below 40°C. It will turn off when the temperature becomes greater than 40°C.? An orange LED will turn on when the temperature increases past 40°C. (i.e. When the green LED turns off.)? A red LED will turn on when the temperature increases past 100°C.When temperature is decreasing:? Once the red LED has been turned on, it will not turn off until the temperature decreases below 80°C.? Once the orange LED turns on, it will not turn off until the temperature drops below 30°C.? The green LED will turn on again when the orange LED turns off (at 30°C).We used our knowledge of diodes and comparators to develop a three state system based upon the input from the temperature gauge. This report will outline our system design and results from our project.Circuit Diagram and ExplanationWe decided a three state system dependent on the output voltage of the temperature measurement sensor in the system would be the simplest way to tackle the problem. The states in our system can be seen in Table 1. Only one LED is on at each state in the system to indicate either low voltage, medium, or high voltage output from the temperature measurement sensor. We calculated the state change points based upon the voltage output from the temperature measurement sensor. The output of the sensor is a DC voltage that is proportional to temperature in degrees Celsius where Vo = 10mV/C * T. We used the equation to calculate the voltages at which each state change occurs to meet our requirements of the lab. These values can be seen in Table 1.StateTemp. to High (C°)Voltage to High(V)Temp. to Low (C°)Corresponding voltage to low (V)Green LED on<40<.430.3Orange LED on40.480.8Red LED on1001n/an/aTable 1: State system with state change voltage pointsUsing the values in Table 1 we designed a simple state machine by adding two comparators in parallel. Three LED’s are connected to the output of the comparators. At the voltage levels listed in Table 1 the state machine will switch and the LED illuminated will change. We used Equation 1 and Equation 2 to calculate the points at which the comparators would switch from low voltage to high voltage and high voltage to low voltage. We used the two equations to derive the resistor ratio needed to successfully create our state machine and turn the LEDs on at the appropriate voltages found in Table 1. Equation 1: Voltage equation for comparator switching to low state from highEquation 2: Voltage equation for comparator switching to high state from lowWe powered the first op amp with a +-8V DC signal to give us enough power to turn on the diodes. We powered the second op amp with +8V and -0V signal because we only needed to power on one more diode and did not want that op amp to send a negative voltage back through the second diode. Using these values for Vp and Vn we were able to take the desired values for Vtl and Vth and calculate resistor ratios that would give us the appropriate switching points for our circuit. The calculations and ratios can be seen below in Table paratorEquationsResistor RatioResistor values used (Ohms)Comparator 1Vtl(1) = .35(161/160) – (8/160) = .3022 VVth(1) = .35(161/160) + (8/160) = .4022 V1/160Ra : 1k? Rb : 160k?Comparator 2Vtl(2) = 1(41/40) – (8/40) = .825 VVth(2) = 1(41/40) + (0/40) = 1.025 V1/40Ra : 1k? Rb : 40k?Table 2: Comparator calculations for Vth and VtlOnce we determined our resistor ratios we built the state machine using two comparators and three diodes in series at the output. The final circuit design can be seen in Figure 1.We also added a voltage divider at the end of our circuit. This voltage divider let us regulate the voltage through the system when both comparators were at their high outputs. If we did not use the voltage divider we found that the yellow and red LEDs both stayed on. The voltage divider brought the output voltage down while comparator 1 was on and comparator 2 was off, enabling us to keep the orange LED on and the Red LED off until Comparator 2 switched on. When Comparator 2 switches on the voltage across the orange LED becomes zero since both op amps are outputting 8V.Figure 1: Circuit designPhoto of Physical CircuitFigure 2: Picture of final circuitOutput of circuitOur final circuit worked flawlessly. We measured the points at which each state (LED) turned on based upon the input voltage to the system which was the output voltage of the temperature measurement device. Table 3 shows the measured points from our circuit.Table 3: Measured voltage switching points in circuitConclusionThis design lab went very smoothly. The most difficult part was calculating the right resistor ratio to give us the appropriate output the power the diodes at different levels, but our calculations worked and we saw the diodes turn on and off at the correct points. Our voltage levels were very accurate and we meet all of the requirements of this lab. We also were able to turn off the orange LED when the red LED was turned on which was an extra challenge in the design project. ................
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