EE 40 Spring 2005 Final Project EE 40 Final Project Part I General instruction 1 The final project will count 30 of the lab grading since it s going to take 3 lab sessions All other individual labs will count 70 of the lab grading each of them counts 10 2 This project is composed of a basic part and a creation part Circuit diagram will be provided for the basic part which is required to be finished at the end of the semester There are three creation questions with different complexity and different bonus credits No circuits will be provided for the creation part You have to design the circuit to realize the function by your own using the components that we can supply You are allowed to discuss with other students and your GSIs GSIs can help you analyze if the circuit works but won t give any hints on the design for the first three questions For the last open question you are welcome to do whatever you think will be worth doing using the components we have and discuss any possible function design with your GSIs 3 Every effort must be made to team up as a team of 2 and if necessary you can change session only under special circumstances and approval by head GSI is required for forming a team of 3 or doing it alone Please try to find your lab partners before hand One of your team members will keep the board and the components during the project period Try to protect your progress and keep it in a good condition 4 Every group will get a project kit with a piece of breadboard and all the components Please check with the component list in lab guide part V to see if the kit is complete Keep it in a good condition during the whole project We don t have many extra parts to supply if you lose any of them 5 The grading will be mainly based on the lab report and the circuit functionality Typed lab report is preferred Hand written is also fine but has to be neat and clear Please see part IV for more information on the lab report 6 Lab report is due on May 6th We will have a final competition You may choose to enter the competition to display your work The competition will be held on Friday May 6th 4 6pm with a snack reception The professor and all GSIs will attend this reception competition and select the projects Each group entering the competition must do a 5 10 minutes show and tell First place 1 team TBA Second place 1 team TBA Third place 1 team TBA 1 EE 40 Spring 2005 Final Project Part II Basic Circuit Light Sensor 1 Function analysis P1 P2 R12 R13 Figure 1 Basic circuit diagram 2 EE 40 Spring 2005 Final Project This is a light sensing circuit When there is no light shinning on the circuit mainly the detection part the green and yellow LED will be flashing and they will be out of phase with each other When light is shinning on the circuit mainly the detection part the red LED will start flashing instead of the green and the yellow ones The blue LED will be shining whether light is and is not being detected The whole circuit can be torn down into 6 basic building blocks labeled A E and the block containing the yellow and blue LEDs in the diagram We will analyze them one by one in order to understand the functions A 4 5 V DC power supply The circuit is going to be powered by a 9 V battery but lower DC power is also needed in the circuit Part A is using an op amp to build up a simple voltage follower which gives 4 5 V output Since 4 5 V is half of 9 V resistors R1 and R2 are equal C1 and C2 are filtering capacitors which are usually connected in parallel with the DC output in order to filter out any high frequency AC signal coming from the noise B Square wave oscillator Let s analyze it in a time sequence and use 4 5 V as the voltage reference The circuit diagram can be redrawn as shown in Figure 2 b 4 5V 0V R3 C3 R3 R4 4 5 V 9V V C3 A2 V R4 Vout V A2 V Vout 4 5 V R5 R5 a b Figure 2 Square wave oscillator a with reference at 0 V b with reference at 4 5 V Initially Vout 0 and there is no charge on the capacitor However to the reference 4 5 V Vout 4 5 V and V 4 5 V Since this circuit has a positive feedback loop any slight difference between V and V may make Vout high or low clamped to the power supply value In this initial condition V 4 5 3 R3 V 4 5 V so the R3 R4 EE 40 Spring 2005 Final Project output goes high and get clamped to 4 5 V immediately after the circuit is on Now the circuit is in state 1 Vout 4 5 V V 4 5 R3 and capacitor C3 is being R3 R4 charged from Vout So V is rising up When V is as high as or just slightly higher than V the circuit toggles because of the positive feedback Output will be clamped at 4 5 V since V V Now the circuit is in state 2 Vout 4 5 V and V 4 5 R3 The capacitor is being discharged from Vout And V is falling R3 R4 down When V is as low as V or just slightly lower than V the circuit toggles again because of the positive feedback Then the output is clamped at 4 5 V again V 4 5 R3 and the capacitor is being charged from Vout again R3 R4 Therefore we see that the circuit is toggling between the two states and the output voltage is either 4 5 V or 4 5 V which forms a periodic square wave To understand the oscillation function better we draw wave forms at V V and Vout on the same scale as shown in Figure 3 b It s clear that the threshold voltages of output high and low are 4 5 R3 R3 V and 4 5 V Go back to the original circuit with R3 R4 R3 R4 reference at 0 V We just need to add a DC offset 4 5 V to all the result and waveforms as shown in Figure 3 a The threshold voltages changes to 4 5 2 R3 R4 R4 and 4 5 R3 R4 R3 R4 V 4 5 2R3 R4 R3 R4 V 4 5R3 R3 R4 4 5R3 R3 R4 4 5R4 R3 R4 V 4 5 2R3 R4 R3 R4 t V t Vout 4 5R3 R3 R4 4 5R3 R3 R4 4 5R4 R3 R4 Vout t 9V t 4 5V 4 5 V 0V t t a b Figure 3 …
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