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

Jonathan Foote jtfoote at ieee.org
Fri Dec 11 19:17:23 UTC 2009


In that case, Lamont's circuit should work pretty well. You might want
a log function in there to match human pitch perception. One of the
bargraph chips (forget the number) has a log response.

On Fri, Dec 11, 2009 at 11:10 AM, Michael Shiloh
<michaelshiloh1010 at gmail.com> wrote:
> in my case, it is a square-ish wave (555 oscillator) and so is
> absolutely not a pure (sine) wave.
>
> Jonathan Foote wrote:
>> 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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