Here is a simple car battery voltmeter circuit using LEDs that can be easily installed in cars. This circuit consists of four LEDs and a quad operational amplifier IC LM 324 as its main part. This circuit is meant for displaying the output voltage of the car battery in a LED dot display format.
The four operational amplifiers in IC LM 324 is used here as comparators. The inverting input pins (pins 2, 6, 9, 13) are kept at reference voltages 5.6V, 5.2V, 4.8V, and 4.4V respectively by using zener diode D1and resistors R3, R4, R5, and R6 as shown in the circuit diagram. The battery voltage is given to the non inverting inputs of comparators through voltage divider network consisting of resistors R1 and R7. According to the level of voltage the output of comparators go high and hence the corresponding LEDs will glow.
- Use a good quality PCB to assemble this circuit.
- Use common power supply for 4 op amps in IC LM 324.
- Adjust potentiometer R6 and make sure that required voltages are available at the inverting pins.
- Fix the LED’s on the dash board and mark the voltages near to it as shown in circuit.