DIY DO-IT-YOURSELF LIE DETECTOR

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A simple detector that will show whether a person is lying or tells the truth. Of course, he is far from a real, modern lie detector - a polygraph, but he deserves attention, since anyone can do it with his own hands. 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 readings that the detector tracks. And already the detector operator determines whether to take these readings into account or not.

The principle of determining lies

The device is a threshold detector that measures the resistance of a portion of the human body. The device reacts to a change in this resistance, and, depending on the indication, changes the state of the indicator.
In general, the resistance of the human body is by no means constant, it depends on many factors. Thanks to this property, we will monitor a sharp change in this value.

What you need to build a lie detector

I 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 analogues of KT315, KT3102, or any other of the same structure.

Simple polygraph diagram

The circuit is built on three transistors. The first transistor is a DC amplifier. On the other two, a Schmitt trigger is built, which can be stably in one of two states: a lie is true.
Using a variable resistor, the threshold is set.

Lie detector sensors

To take readings from a person we need two sensors. I made them Velcro clothes by gluing aluminum foil to the back and connecting the wires to it.
The sensors can be of another design, the main thing is that they have a large area of contact of the live part with the human body.

Circuit assembly

I assembled the circuit on a breadboard. Added a switch and a capacitor to the power, which are not on the circuit. I think it will be better and more stable, although you can do without all this.

Detector housing

The case was made of a tin box. I drilled a hole for a variable resistor. I put a piece of cardboard at the bottom so that the board does not close to the case. He glued the switch with hot glue, supported the battery with a piece of insulation. Common (minus) connected to the body. The design turned out to be shielded and its interference is not terrible.

Everything is ready - tests

Your lie detector is now ready for use. Put on the fingers of the "suspect" sensors.
Turn on the power circuit. Turn the variable resistor gently until the green (True) lights up and the red (false) goes out. This will be the threshold.
Ask the "suspect" a question. If after a few seconds the red lights up, it is lying.

Enjoy the result of robots!

The detector is small and you can take it with you anywhere. It is fully functional and fully operational.
You will definitely get a lot of pleasure after assembly and testing.