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

[Jonathan Foote]

A number of ways to do this, sadly none are that simple.

Classic approach is an array of bandpass filters. You then rectify the
output of each and take the log. Straightforward but requires lots of
circuitry, as each channel needs at least a second-order bandpass (and
works better with higher orders).

Another way is to heterodyne the frequencies of interest down to DC.
(Check out this glorious old-school spectrograph:
 http://www.sfu.ca/sonic-studio/handbook/Spectrograph.html)

The easiest way is to use a windowed FFT, then take the log of the
magnitude of the output.
(Using SciPy, you can do this in 3 lines of Python, so that method
gets my vote. )



On Thu, Dec 10, 2009 at 8:55 PM, Michael Shiloh
<michaelshiloh1010 at gmail.com> wrote:
> a student wants to build a bar graph type display that will show
> frequency, not voltage. the frequency is in the audio range.
>
> i know there are chips to do this, but i'd like to find a circuit using
> more basic and common components, like a 555, 741, 2n2222, etc.
>
> precision and linearity is not an issue. it's merely a visual element.
>
> any ideas?
> _______________________________________________
> Noisebridge-discuss mailing list
> Noisebridge-discuss at lists.noisebridge.net
> https://www.noisebridge.net/mailman/listinfo/noisebridge-discuss
>