Voltage to Frequency Converter Circuit

This voltage to frequency converter circuit has an oscillator that is voltage controlled and has a small, 0.5% deviation. IC1 function as a multivibrator and produces rectangular impulses with equal width.
The width of the impulses depend on R4, P1 and C1. With P1 we can do fine adjustments of the output frequency.

The output frequency can be easily adjusted with the help of U1 voltage. D3 diode is required because we want to eliminate R4 and P1 influence. D1 and D2 diodes produce a small flow of temperature. With P2 we adjust the offset voltage. Because of its high quality, this voltage-frequency converter (VCO) can be used in a large field of applications.


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Voltage-Frequency Converter Circuit Diagram


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  • sanjay agarwal

    can you suggest me d.c. multiplier ckt based on discrete ircuit.

    sanjay agarawal


    one Ic No. Intech A-8400 for voltage to frequency/frequency to voltage converter is used on board in cylindrical grinder machine and this IC is absolute . please give the solution.

    • Jim Keith

      No simple solution because this chip is not only obsolete–it is unavailable. There is no replacement. The closest device that I know of is the Fairchild ua7141 that is also unavailable. I located the datasheet for the A-8400:

      Any replacement must be in the form of a PCB module that is compatible with the A-8400 pinout–there must be space available for such. The module would consist of the Exar XR4151 F-V-F IC and op amp. Not knowing the exact application or having the machine schematic, the application specific issues cannot be properly engineered.

      Another approach is to attempt to locate a similar machine that can be used for parts.

  • Ed

    To Jim: guess I lost you through my exsplanation. I found out how to build it via a downloadable app, so now onto building. Thanks though

  • Jim Keith

    About 0 to 10kHZ per info at top of schematic.

    • Ed

      Hi Jim, thanks for the reply. Though I am old, and been at this a while now, seems the math involved in electronics takes all the want to out of me on alot of projects. I get alot out of accomplishing working circuits, but the math has never been something that ever stuck with me, even with the use of calculators, I have to re-read the process over and over to formulate an anserw.
      I am trying to get a 2450Mhz circuit put together. My eyes suck, but have been trying to reverse engineer a salvaged Microwave oven circuit board to find out how to resonate an old M.O.T. for an exsperiment I am doing. I cannot tell on some of the boards I have if it is the Ic doing the oscillations or the pezio buzzer or some other HF switching triac Any Ideas? All the salvaged boards, “I have three” are from digital display and have dig processors on the same boards,,,so far I have found no switching transistors so I assume one of the IC chips involved is the “VIBRATOR” Oscillator. Would this circuit with modifications to the RC or replaced with LC work?

    • Jim Keith

      The magnetron oscillator tube generates its own RF –this happens automatically when high voltage DC is applied –about 700 to 1000V, I think. So what you have to find is the triac or SCR that controls the power to the tube. The basic power supply circuit escapes me at the moment.

      The amplitron tube is similar, but designed to amplify the microwave signal generated by a magnetron. These are used in high power radar transmitters.

    • Ed

      Thanks again Jim, I am not wanting to build microwave oven or transmit a signal, I came to Mhz because of a video I saw. It required the same Hz as used for Microwave Ovens. I have alot of old stuff I salvaged “electronics” and began looking at C-boards to see HOW it was done.
      About 3 years ago, I was waiting on some help from a nieghbor with my water well, years earlier I had been trying to release the H molecule from H20,
      and while waiting on this friend I was at my bench and looking over an old Cell I had built, also at my bench was a “Coleman tm” 1500watt inverter and home built fullwave bridge rectifyer so I began messing around with those and a 12v truck battery, a quart of Distilled water.
      I used half the brige and that quart cell of water vanished almost instantly,,,NO STEAM!
      I was amazed. it was like you shook a hot unopened can of beer
      in the middle of the Sahara and opened it! only this was a quart sized open 4″ S.S. 8″ long pipe with a capped bottem to hold the water in the cell. Since then I have been trying to duplicate this method but with a bit more control, because it was toooo fast, and produced heat after refilling over and over with distilled water. I saw a guy who might have hit on the same methode who is in the process of commercialing it so he is secretive in the method process, but 2450Mhz was communicated during the video.
      Now that I have that lenghtly exsplanation out there, how do I do this Oscillation circuit?

  • Ed

    can you tell us,,what is the range of frequency capable with a circuit like this?

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