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:
