Wiring Schematic diagram

The battery indicator can monitor the voltage on the car battery. The indicator has four LEDs that indicate the voltage. The more LEDs, the higher the voltage. The last LED is a blinking LED. This lights up when the battery voltage exceeds the limit of about 15 V. 

This is a sign that something is wrong with the alternator or voltage regulator. The other LEDs light up respectively at 9 V (D5: bad battery), 11 V (D7: battery doubtful) and 13 V (D9: battery ok).Build the the activation points above. Circuit and verify If the measured values ​​are much different from the above, try other Zener diodes. Zeners 300 mW are sufficient for the circuit.

Parts List

     D1, D2, D3, D4 = 1N4002
     D5 = LED green
     D7 = LED yellow
     D9 = LED red
     D11 = LED flashing
     Zener diode D6 = 4.7 V/300 mW
     D8 = 6.2 V/300 mW Zener diode
     D10 = 9.1 V/300 mW Zener diode
     D12 = 5.1 V/300 mW Zener diode
     T1, T2, T3, T4 = BF 256B