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  • Portable Lie Detector

  • Created: Sep 17, 2014

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Lie detection is a process often used by authorities to help them on their investigated subject on questioning. There are a wide variety of technologies available using different methods, but the idea is all the same; the authority uses questioning techniques along with technology that record physiological functions to ascertain truth and falsehood in response.

This project is a simple device, its concept is adapted from polygraph that detects the automatic reaction of the subject. The changes in body functions are not easily controlled by the conscious mind and include bodily reactions like skin conductivity.

The device has two strobes to be placed on the two fingers of the subject, a variable resistor must be adjusted first to set the initial resistance since different subject have different resistivity. In the initial setup, the TRUE LED must be turned ON and the FALSE LED is OFF. The first 2N3904 transistor will act as a buffer and the other two 2N3904 transistor will act as a comparator. If the voltage at the base of second transistor is higher than at the base of third transistor then the TRUE LED will light ON. If the reverse is true then the FALSE LED will light. When the subject will lie, there will also a change in skin conductivity and the The voltage at the base of third transistor will be greater than the second transistor and the FALSE LED turns ON.



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