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BMEN 3350 Homework 1

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Homework 1 - Solution Problem 1 (15 points): Design a circuit with one input voltage, V in , such that,  a red LED lights up when V in exceeds +3 V  a green LED lights up when V in exceeds +8 V The LEDs each have a forward voltage drop of 1.5 V and maximum current limit of 25 mA. You can only use one voltage source with V S = 10 V. You can use any number of resistors and op amps. Clearly draw the circuit and show the component values. Solution: There are multiple ways of designing this; below is one solution. For each op amp: use +10 V and 0 V (i.e. ground of the source) as supply voltages, V DD and V SS , respectively. L2 is red LED, L1 is green. Choose, Vcc = 10 V. R1, R2, R3 will have the ratio 2:5:3. 10−1.5 R6 and R7 are each = 340 Ohms or more.