Uses a 12 Volts DC Car Battery. The principle is, if the circuit Falls down the desired value (12 Volts) the LED indicates turn ON and the transistor NPN conducts when the Voltage Fall down below 12 Volts. Best Application are for car batteries, Changing the circuit parameters it might also used for Cellular Phones, the red Light will indicate if Battery is Low and Fall down the operating Limit. Uses the Variable Resistor to Change variably the flow of current in the circuit,Turn the potentiometer left and right and see the difference. some uses sensors, for sensing low voltage.
