Schematics Depot >> Power >> 12v battery monitor

12v battery monitor:

R110k ohm potentiometer
R2, R31k ohm resistor
D16 volt zener, 1 watt
Q12N3904 npn transistor
LED1light emitting diode

all resistors are 5 or 10 percent tolerance, 1/4-watt
R1 controls the trip-point of the circuit. when the voltage falls below the trip-point, the led lights. adjust it to the desired level. to use this circuit to monitor a 6v battery, substitute D1 for a 3.3 volt zener diode and adjust R1 accordingly.
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