op amp based frequency to voltage conversion

Discussion in 'The Projects Forum' started by garry.owens, Dec 17, 2008.

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i am at the moment trying to work on a signal gen and i am trying to keep the cost to a min so i am looking to convert frequency to voltage so that i may use a volt meter insted of a frequency counter in my project dose any one know of a circuit that doese this using a op amp or simular as i have several op amps in my box thank you

2. beenthere Retired Moderator

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Look into an LM2907. It's a specialized IC that does F tp V conversion.

If you have an accurate time base, it is also pretty simple to use some counter IC's to make a frequency counter. That is much more accurate than the frequency to voltage conversion.

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this i know althow i have not used modern frequency chips and admid am a little aprehensive at some of them the reson that i was thinking of a 741 is that i have several of these in my spares box and was hoping to save some cash thank you for taking the troble to answer and if i get nothing else i will have to go down this rout althou i would rather not as cash flow at the moment is to say the least tight gasser

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Hello,

An frequency to voltage converter can be made with an monostabile multivibrator like a 555, followed by an intergrator wich can be made with the old 741.
What happens ia as followed :
You make pulses of equal width.
The higher the frequency the higher the number of pulses.
By intergrating them you get a voltage dependend on the number of pulses.

Greetings,
Bertus

5. studiot AAC Fanatic!

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What sort of sig gen?

All the solutions quoted so far a pretty low frequency.

What means do you have to calibrate?

Integrating current is better than integrating voltage. the following will give you a reasonably linear four range frequency scale, to 100Khz.

• fmeter.jpg
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this is just audio frequency up to a max of 20KHZ an i will be using the ocuilascope to callabrait thangk you all for youre quick replys the sig gen i am using is a pic programed unit

7. kahafeez Active Member

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hi just to add my part..... i did this earlier..... it was BFSK demodulation.... the principle is same..... u've to detect the freq and convert it into high or low amplitude.... i used PLL.... there is this ic called NE565 or LM565(both are same)..... it can detect upto 500KHz..... and its cheap too.... and it should be accurate as it is a coherent detector....

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Hello,

When you use a 555 that makes pulses of about 40 μSeconds,
you could measure upto 25 kHz.

The lowest frequency is depending on the intergrator,
as it will fluctuate more at lower frequencies.

Greetings,
Bertus

PS mind you typing, it looks rather odd and does make it more difficult to understand.