A simple lie detector that is based on well-known principle of Biofeedback can be designed using this electronic circuit diagram.
This lie detector circuit described eally give two readings: one for the difficult questions and one show subject general emotional state. As electrodes can be used two flexible wires, uninsulated wrapped around the fingers or wrist.
This battery voltage indicator electronic project is designed using linear voltage indicator SN16889 (manufactured by Texas Instruments) or MC16889 (manufactured by Motorola). The circuit below allows lighting, depending on input voltage of one or more LEDs. Maximum voltage at which all LEDs light is adjusted using potentiometer P1 to 15 volts. D7 can be red LED indicates a battery voltage too high. D6 LED green indicates a correct value and the battery voltage LEDs D5, D4 and D3 yellow indicates a battery voltage too low.
A drop voltage indicator can be designed using electronic diagram below. This indicator shows the drop voltage or disturbing impulses of any existing network using a LED which will light.
This circuit can be powered with a DC voltage between 5 and 12 volts.