Simple LED Voltmeter

Four µ741 op-amps are used here to measure the voltage ranging from 3V to 12V DC. The voltage measured is displayed on eight LEDs.

The inverting inputs (pin 2) of IC1 through IC4 are supplied with regulated 12V DC through voltage dividers R1 through R4. So the inverting input of each op-amp forms the reference voltage. The non-inverting inputs (pin 3) of the op-amps are tied together and connected to the input terminals. The voltage to be meaured is fed to these input terminals.

When the input voltage exceeds the reference voltage of any of the op-amps, its output goes high, making the corresponding LEDs to glow.

This circuit is designed to measure 3V, 6V, 9V and 12V DC. For instance, when the input voltage is 3V, LED7 and LED8 glow. When the input voltage is 12V, all the LEDs glow.

Note. You can use a quad device such as LM324 instead of µ741 ICs.

Circuit Diagram:

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