Miscellaneous sensor schematics
Simple Lie Detector
Here's a simple lie detector that can be built in a few minutes, but can be incredibly useful when you want to know if someone is really telling you the truth. It is not as sophisticated as the ones the professionals use, but it works. It works by measuring skin resistance, which goes down when you lie....
The piezoelectric element of a kitchen gas lighter is used in this simple, yet effective seismic detector. The piezo element must be placed vertically, one end solidly to ground....
Static Electricity / Negative Ion Detector
This circuit relies upon the extra high input impedance of a FET, and also demonstrates
the gate terminals sensitivity to changes in voltage. The gate terminal here is left open circuit, connected only to the "probe" this being just a few inches of bare copper wire....