Simple Lie Detector
A simple detector that will show whether a person is lying or telling the truth. Of course, he is far from the present, modern lie detector - a polygraph, but it deserves attention, since anyone who can do it himself can make it. Like any, even the most modern polygraph, it does not show 100% that a person is lying. It shows that the human body has changed its state, in the indications that the detector tracks. And the detector operator already determines whether these readings are taken into account or not.
Principle of lie detectionThe device is a threshold detector that measures the resistance of a part of the human body. The device responds to changes in this resistance, and depending on the indication changes the state of the indicator. In general, the resistance of the human body is not constant, it depends on many factors. Thanks to this property, we will track a sharp change in this value.
What is needed to build a lie detectorI will not list all the elements - they can be seen in the diagram.There are no special requirements for them - you can use any. Transistors 2N3904, domestic analogs of KT315, KT3102, or any others of the same structure.
Simple polygraph circuitThe circuit is built on three transistors. The first transistor is a DC amplifier. The other two are built Schmitt trigger, which can stably be in one of two states: false - true. With a variable resistor threshold is configured.
Lie-detector sensorsTo take readings from a person, we need two sensors. I made their clothes velcro by gluing aluminum foil to the back side and connecting wires to it. The sensors can be of another design, as long as they have a large area of contact between the current-carrying part and the human body.
Assembling the circuitThe circuit is assembled on a breadboard. Added a switch and a capacitor for power, which is not on the diagram.I think it will be better and more stable, although you can do without all this.
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