Lie Detector

 

This is a false capture circuit or Lie detector circuit. The basic principle of the resistance of human skin. While dry skin is a resistance of about 1 Mega ohm but if the skin moisture resistance is reduced. When the body are excited or scared or not sure the skin is moist than usual.

Operation of the circuit is a circuit of R1 and R2 divide the line voltage and probe used to measure the resistance of the skin, which is parallel with R2.So voltage drop across R2 is based on the resistance of the skin with is if the skin dry (people do not lie), the resistance of about 1 mega ohm to a strong drop across about 4.5 volt, but if the skin moist (liar), the resistance is less than 1 mega ohm to a voltage drop across less than 4.5 volts.It uses the pressure is on bias voltage to flow in Q1 – BC548, where Q1 and R3 buffer circuit to circuit.