Free Circuit Diagram

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 the someone who telling lie but it is not as sophisticated as the ones the professionals use. Here is the schematic diagram of this circuit:

The skin resistance [...]

To build a heart-beat transducer not as difficult as imagined. Circuit below shows a simple heart-beat transducer.

This circuit made from an infrared phototransistor and infrared LED.  This transducer works with the principle of light reflection,in this case the light is infrared.  The skin is used as a reflective surface for infrared light. The density of [...]