This simple lie detector circuit implementing human skin conductivity which varies according to the condition of the emotions. You can easily created with just a few minutes and cheap.
This is how simple lie detector work : The circuit uses an oscillator that has a frequency based on C1, R2, and skin resistance at the touch pad. Because C1 and R2 value is fixed, only the skin resistance at the touch pad that can change the tone oscillator. To maintain oscillation, the C1 provides some output from Q2 back to the input of Q1 through R1.
Q1 is NPN type transistor and Q2 is PNP type transistor. Output Q2 is given to a small speaker.
Part List :
C1 = 10 nFPart List :
R1 = 4K7 ohm
R2 = 82 kohm
Q1 = 2N3904
Q2 = 2N3906
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