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The Projects Forum Working on an electronics project and would like some suggestions, help or critiques? If you would like to comment or assist others with their projects, this is the place to do it.

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  #1  
Old 12-17-2008, 02:11 PM
garry.owens garry.owens is offline
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Default op amp based frequency to voltage conversion

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
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Old 12-17-2008, 03:59 PM
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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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Old 12-17-2008, 04:31 PM
garry.owens garry.owens is offline
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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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Old 12-17-2008, 05:16 PM
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bertus bertus is offline
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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
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Old 12-17-2008, 10:37 PM
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Quote:
signal gen
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.
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Old 12-18-2008, 07:56 PM
garry.owens garry.owens is offline
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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
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Old 12-19-2008, 12:46 AM
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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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Old 12-19-2008, 08:29 AM
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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.
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Old 12-20-2008, 09:12 AM
garry.owens garry.owens is offline
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thank you all for you're help i do apologise for the typos but im not a keyboard person but i will take more care in the future
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