This is a circuit diagram of the 3 LED bar graph type battery monitor ideal for monitoring the voltage level of the car battery voltage with battery.
When the battery voltage is 11.5V or less transistor Q1 is turned on and the LED D1 will be bright. When the battery voltage is between 11.5 and 13.5 V, the transistor Q2 is turned on and the LED D2 will light up. When the battery voltage is 13.5V transistor Q3 will be on the D3 and the LED will light.
Car Battery Monitor Parts list :
R1, R3, R6 = 1K
R2 = 100K
R4, R5, R7, R8 = 3.3K
D1,D2,D7 = LED
D3, D4 , D5, D8, D9 = 1N4148
D10 = BZX79C12
Q1, Q2 = BC547
Q3 = BC557
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