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[SOLVED] 4538 Monostable multivibrator F/V converter

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elisemark

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anyone has a working example in which the 4538Monostable was used for frequency to voltage conversion ?
 

**broken link removed**

Look on page 7.
 
Thanks KJ6EAD ,
from the document you pointed to the maximum input signal is determined by the time constant so in this case it is 10 KHz because Fmax=1/tau=1/(0.001uF*10Kohms) =10Khz .
help me understand one more thing , it looks like the input must be a square wave and in my case I have a sinewave FM moculated signal around 1.2MHz. how do I move forward with this ?
Thanks
 

There are many ways to accomplish the sine to square wave conversion. Which is appropriate for your application will depend on the amplitude and frequency of your input signal. Here's a paper that describes a few of the methods: **broken link removed**.

It appears that the 14538B device may not be fast enough for that frequency even after modifying the RC time constant, though the 4538A or 14528B may.

In summary: you need to demodulate, convert to square wave, then convert frequency to voltage in that order. You also will probably need to attenuate or amplify to the correct level before or during the conversion to square wave.
 
Thanks for your input.
looks like applying a scmitt trigger may work better and easier than the other methods. how about using a frequency divider such as 4040 IC in order to bring the signal in a proper range that the 4538 series can handle ? for demodulation is PLL ICs the best way to do it ?
 

The 4040 sounds reasonable, if needed. You were thinking of 4046 for demodulation? It's not my area of expertise.
 
Again thanks for your feedback , yes for demodulation I was thinking of the 4046 but if there is any other method that is simpler I would like to try those . I know I could even use just the 4046 for the whole thing and not need another F/V ic but the loop filter design did not work well for me . so if any other demodulation methods are available I would welcome those before going back to the 4046 .
Thanks
 

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