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Homework Help: Electronic Switch / Microphone

  1. Sep 5, 2012 #1
    1. The problem statement, all variables and given/known data
    You're given an electronic switch which requires 5V at 1mA in order to close; it is open with no voltage present at its input. If the only microphone available produces a peak voltage of 250mV, design a circuit which will energize the switch when someone speaks into the microphone.

    2. Relevant equations

    3. The attempt at a solution
    I really don't know how to start. Would I use an instrumentation amplifier or something else? If so, how would it be wired? Where would the signal from the microphone go?

  2. jcsd
  3. Sep 5, 2012 #2


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    Staff: Mentor

    You do need to amplify the signal, then detect when it is above some threshold, and have that detection trigger the drive to the relay and hold that drive steady for some time period (like for the duration of the speaking plus a couple of seconds maybe). The amplification does not need to be high fidelity -- you are just looking for when the signal from the microphone is above some detection threshold...
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