Simple lie detector circuit design electronic project
A simple lie detector that is based on well-known principle of Biofeedback can be designed using this electronic circuit diagram.
This lie detector circuit described eally give two readings: one for the difficult questions and one show subject general emotional state. As electrodes can be used two flexible wires, uninsulated wrapped around the fingers or wrist.
Each change of resistance, and therefore the voltage at the input circuit will be amplified by operational amplifier A1, which is also an upstairs separately corresponding output signal will, by R3, a deviation of the measuring device.
Operational amplifier A2 is connected as an integrator and allows the circuit to automatically adjust according to the average resistance of the skin. The length of time in skin resistance to be measured is determined by R5, C2 and C3. Until this time elapses, the gauge does not give any indication, though diodes D1 and D3 ensure a rapid response of the circuit.
P1 potentiometer allows adjustment of time delay circuit. Because skin resistance varies from person to person, it may be necessary to change the resistance value R1. This resistance can be replaced by a potentiometer. Read a great value to the instrument connected to port B indicates that the subject's skin resistance is low.