Lie Detector Circuit

Lie Detectors are electronic circuits that are able to measure your skin’s resistance. When you sweat (or if your skin is wet), the resistance is different than if it’s dry.

However since most people don’t sweat when they lie, this type of detector isn’t the most reliable type of detector around, but it’s one of the simplest to create. We’re going to build one from simple electronic components like resistors, capacitors, and transistors.

Our lie detector uses a speaker that changes pitch depending on the resistance of your skin – it’s much more entertaining than blinking an LED on or off. You can think of this circuit as more of a skin humidity indicator. Are you ready?

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8 Responses to “Lie Detector Circuit”
  1. Aurora says:

    The base of the PNP is very sensitive (it’s an amplifier transitor) and its measuring tiny fluctuations in resistance between two probes. When someone lies, their skin tends to become more moist (more conductive) which turns the PNP on which changes the tone in the speaker.

  2. tsyed says:

    how does it detect lying? doesn’t it make noise if you touch and your not lying?

  3. Aurora says:

    I would remove it from the circuit and build the circuit again. Sounds like you ran power to the wrong leads. Try again! It happens to everyone.

  4. Candyce Ovadal says:

    My 2N3906 transistor got hot and my speaker didn’t make any noise. How can I fix it?

  5. Sabrina Larkin says:

    wooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooow !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

  6. Sharalee Jaenke says:

    w00000000000000000000000000000000000000000000000000000000000000000000000w I like to say w00000000000000000000000000000000000000000000000000000000000000000000000w too

  7. Martin Melody says:

    coooool I LOVE IT

  8. Martin Melody says:


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