Battery Voltage State Indicator using 741

Here is a simple circuit using op-amp 741 called “Battery voltage state indicator” used to indicate whether the battery is charged or not. The circuit shows three state of battery voltage i.e. charged, discharged and normal using three different color LEDs (LED1, LED2 and LED3).

Circuit Description of Battery Voltage State Indicator

The circuit of battery voltage state indicator is build around very popular and low costs op-amp IC 741. This circuit uses two op-amps in comparator mode, which compare the battery voltage with references voltage. The battery voltage is connected to E (pin 2 of IC1 and pin 3 of IC2) as show in circuit diagram, which further compares with reference voltage E1 and E2.

circuit diagram of battery voltage state indicator

If the battery voltage is less then 11V, LED2 glow, similarly if battery voltage is 11V to 13V LED3 glow and if the battery voltage is greater than 13V LED1 glow.

The variable resistors VR1 and VR2 is so adjusted that the voltage between pin 2 of IC1 and earth is 13V and voltage between pin 3 of IC3 and earth I 11V.

Resistor (all ¼-watt, ± 5% Carbon)
R1 – R3 = 2.7 KΩ

VR1, VR2 = 22 KΩ

Semiconductors
IC1, IC3 = 741

D1, D2 = 1N4148

LED1 = Red LED

LED2 = Orange LED

LED3 = Green LED

 

  • firdaintani

    What if I use it to check the 220 V or more? What if I change the VR to 10k?

  • kg

    is the project practically tested???

  • ANSHUL BANSAL 15BEE0282

    Plz explain the working of this project…

    • The circuit posted here uses two op-amp in comparator mode i.e. which compare the input voltage with reference voltage and display the output.

  • ABHISHEK

    what the purpose of IC1 pin no 3 & IC2 pin no 2 connect E that E means

    • As i had mention in Circuit description section The battery voltage (whose voltage should me measured) is connected to E (pin 2 of IC1 and pin 3 of IC2) as show in circuit diagram, which further compares with reference voltage E1 and E2.

      • Rama Krishna

        Sir, what do you mean by “E1” and “E2”

        • E1 and E2 is the refrence voltage given to both op-amp IC.

  • Surya Datta

    how did 11v and 13v come at pins when we gave 9v input..

    • The 9V input is the power supply for the functioning of circuit.
      Similarly, 11v and 13v is the voltage of battery whose state (low or need charge or full charge) is to be indicate.

  • Surya Datta

    thanq sir, what should be connected to pin 3 of ic1 and pin 2 of ic2

  • Srinivasa Sravan Datta M

    sir what we have to connect to pin3 of ic1 anf pin2 of ic2…..
    suppose that we have to check the condition of a 15v battery…
    you are telling to maintain 13v and 11v using variable resistrs…..
    am i correct ???

  • Surya Datta

    sir…!!!
    please answer what should we connect to pin 3 of ic1 and pin 2 of ic2

  • Varun Meka

    do we need to adjust voltages e1 and e2 using potentiometer every time after changing the input e

  • Varun Meka

    can i use any led instead of given ones