This simple 4 LED car voltmeter is designed to allow us to monitor the voltage level of the battery of our car at any instant, continuously.
Submitted: R.K. Singh
To achieve the above feature it must be placed somewhere in the dash of the car so that the group of 4 LEDs remain protruded, each with a label indicating the battery voltage having at that instant.The circuit is designed for executing the following:
- 1st LED lights with 11V battery
- 1st and 2nd LEDs light with battery 12V
- 1st, 2nd and 3rd LEDs light with battery 13V
- 1st, 2nd, 3rd and 4th (all) LEDs light with battery 14V
When the battery voltage drops to 11 or 12 volts, it may need charging. If its around 13 volts it is in acceptable condition. At 14 volts it is fully charged. The colors of the LEDs indicate these status.
The main components of the circuit are just a few operational amplifiers used as comparators.
The inverting inputs of these operational are set at fixed reference voltages: 5.1, 4.8, 4.4, 4.1 using zener diode D1 and resistor network: R1, R2, R3 and VR potentiometer.
The VR potentiometer is used to make minor adjustments to the above referenced voltages, which could vary because the resistors are not exact values.
The battery voltage is delivered to non-inverting inputs of the opamps through the shown voltage divider networks formed by R4 and R6 terminals.
Depending on the battery voltage, the voltage at the non-inverting terminal will vary and will put a high voltage level at the output of the comparator, activating the corresponding LED for the required indications.
Parts list for the circuit
- IC1: LM324 integrated (quad opamps in a single integrated) Circuit
- D1: 3.3V zener diode, 1/4 watt
- D2 = D3 = D4 = D5: Diodes LED (2 red, 1 yellow or amber, 1 green)
- R1 = 1K
- R2.....R6: all 1K preset
+12V: is the car battery whose voltage is to be sensed