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.
Simple Accu Indicator Circuit Diagram
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
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