Simple Lie Detector Circuit

If you want to know someone is lying or not we can use lie detector. This is a simple lie detector that can be made in minutes. It works to detect someone who telling lie but it is not as sophisticated as the ones the professionals use. This is the figure of the circuit;

The skin resistance will go down when someone telling lie and this circuit works by measuring it. We can use electrode pads, alligator clips, or just wires and tape as the electrodes. We have to adjust R2 to position the meter at the center at the beginning of the interrogation (relax condition), then we can know someone is lying when the meter changes in response to a question.

[Schematic circuit source: aaroncake.net]

Simple Remote Sensor System Pre-Amp

| author: Free schematics and tools

This is a design circuit for remote sensor might cause a trouble if it’s a passive type, has very low power output, and should be connected with relatively long cables. By supplying a current or voltage source through its connection wire, it’s possible to make long enough wiring without suffering much noise/interference. The following schematic diagram show a circuit consist of LM10 to make a remote vibration sensor connection works fine. We don’t need a separate wires for signal and power supply, we send them on the same cable pair. This is the figure of the circuit;

[Circuit diagram source: National Semiconductor Application Notes]

Simple Humidity Sensor Circuit

This is a humidity sensor to give an alert of boat leakage, or when your books start being flooded by heavy rain attack on your broken roof, or anything you can imagine. A simple humidity sensor (a humidity probe) can be constructed using two copper wires placed as close as possible to each other, but no touching. This simple circuit can be used to make your simple humidity detector. This is the figure of the circuit;

If the humidity increase, the probe resistance will drop and the Schmidt trigger formed by Q1 and Q2 will be triggered, and the Q2 collector become low, this condition will trigger the S-R (set-reset) flip-flop formed by U1A, U1B. After triggered, the relay will remain active until you reset the circuit by pressing the SW1 switch.