Voltage into Frequency Converter

IC 741 is most used and popular operational amplifier IC, because of its unique feature and low price. Various op-amp 741 based projects are already posted in operational amplifier based projects section. Now, here is simple project using couple of op-amp 741 IC called voltage into frequency converter.

Circuit description of voltage into frequency converter

The circuit of voltage into frequency converter consist a couple of op-amp 741, couple of transistor and few passive components (resistors). The voltage of 0.5V to 15V is given to Vin pin 2 of IC1 through VR1 and resistor R1 and is converted to its corresponding frequency. This circuit posted here can also used as voltage measurement in digital form.

circuit diagram of voltage into frequency converter

IC1 is configured in inverter mode and IC2 in schmit trigger mode. The output of IC1 is dependent in input voltage and is given to input of IC2. IC2 become ON and OFF in fixed time interval. The triangle wave is obtained at the output of IC2. Triangle wave is further amplifier and changed into square wave by two transistors T1 and T2. This square wave is given to counter roe reading.


Resistor (all ¼-watt, ± 5% Carbon)

R1 = 1 MΩ

R2 = 18 KΩ

R3 = 10 KΩ

R4 = 220 KΩ

R5 = 100 KΩ

R6 = 2.2 KΩ

R7 = 2.7 KΩ

R8 = 10 KΩ

R9 = 12 KΩ

VR1 = 500 KΩ

VR2 = 5 KΩ


 C1 = 0.1 µF


IC1, IC2 = 741

D1 = 1N34

T1, T2 = BC108




    please tell me where exactly the input is given either 2nd or 3rd terminal of first IC and tell me about the 4th terminal in second IC

  • Pin 2 2 and 3 of IC1 is connected as shown in circuit diagram and pin 4 of IC2 is zero potential pin which is not necessary to connect.

    • Muzamil

      Can i use fixed resistor instead of variable resistors used above

  • Mahdieh

    what is vin? pulse or dc

  • i want to know how to check frequency at output

    • You may check using pspice.

      • aditya thota

        sir can i know complete project details of under and over voltage indicator with op amp window comparator

  • Ta

    i think the square wave should be obtained at the output of 2nd IC itself as it is in Schmitt Trigger mode, the transistors ahead just amplify it.

  • somasundaram

    my simulation of the above circuit is not coming correct in multisim

  • rakshith

    what is the formula to calculate frequency theoreticaly

  • talha saeed

    sir,telll us the use of frequency converter and its advantage
    why we need frequency converter.

  • what will be output of voltage into frequency converter by lm 741 ic?

  • Tejaswini

    How to calculate the theatrical frequency?

  • supreetha m s

    How to get the output for voltage to frequency converter?