[Noisebridge-discuss] seeking circuit idea: frequency to voltage

Lamont Lucas lamont at cluepon.com
Fri Dec 11 08:01:48 UTC 2009


Lamont Lucas wrote:
> Use a 555 as a monostable (one shot) vibrator that kicks out a fixed 
> width pulse every time the input voltage crosses zero (or some higher 
> point at the Vthreshold, you know, one fixed-width pulse per input 
> waveform cycle), then a 741 configured as an integrator after that.
>
> As long as your fixed pulse width is less than 1/20000th of a second, 
> and you integrate the output, you should get a output voltage that is 
> linearly related to the input frequency, with higher voltage indicating 
> higher frequency all the way from 0 Hz to 20kHz.
>
> that's a 555, 2 caps, and 3 resistors for the monostable vibrator, plus 
> a 741, a resistor and a cap for the integrator.

Oh, and to go from a linear voltage to a bar graph...hm.  Maybe a 
resistor ladder with LEDs on the legs that will only turn on when the 
voltage at each node in the ladder raises above the forward voltage drop.





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