HW4-1 & 4-2

  • Due Oct 22, 2024 by 11:59pm
  • Points 20
  • Submitting a text entry box or a file upload
  1. Op amps can amplify small voltage differences. This problem is an extension of Problem 4.8 from the textbook.  Given that A=105 and the power supply is +/-10V, what would be the output if…
    1. vs = 1V
    2. vs = -0.5V
    3. vs = 0.00001V

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2. Preparing for Lab 5: In which situation(s) do you expect the LED to turn on?  If Vdd=5V, R=500Ω and the forward voltage of the LED is Vf=2.5V, what is the expected current in each situation?

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3. Op amps can be used to detect small changes in resistance. Here is an example of a Rain or Moisture sensor from[1].  You will be building something similar in Labs 5 & 6.  To use this as a sensor, you would adjust the potentiometer (R2a+R2b) until Vout is around 0V.

    1. Write expressions for Vp and Vn. Leave your answer as a function of variables R1, Rsensor, R2a, and R2b.
    2. If the power supply is +/- 6V and A=105, what change in resistance Rsensor would cause a 5V change in the output voltage? Assume the baseline Rsensor is 1MΩ, R1=1MΩ, and R2a+R2b=1MΩ.  (Starting hint: What do R2a and R2b need to be in order for the sensor to be at 0V to start?)    What % change in resistance is that?

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[1] Forrest M. Mims III, ‘Science & Communication Circuits & Projects’, Master Publishing, Inc.,2007

 

 

 

1729663140 10/22/2024 11:59pm