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

Jonathan Foote jtfoote at ieee.org
Fri Dec 11 18:32:10 UTC 2009


That's only going to work for a pure tone, and not for speech or music.
Typical audio is harmonically rich, meaning lots of frequencies mixed together.


On Fri, Dec 11, 2009 at 12:01 AM, Lamont Lucas <lamont at cluepon.com> wrote:
> 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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