[sdiy] frequency to voltage? (theremin fun)

[marmot1 at magma.ca]

Hi Nils,
I put together one of Harry's PV-1 pitch-voltage converter boards 
(available from Tomg's EFM site). Apparently it works quite nicely with 
a theremin. I use mine to provide an analog one volt/oct CV from a 
homemade digital synth.
Regards, Mike


Nils Pipenbrinck wrote:
> 
> Hi.
> 
> Yesterday I built a little theremin based on a circuit I found in the
> internet somewhere.. It's not the classic circuit.
> 
> Oscillator is built around a cmos hex-inverter, and a cmos pll ic controlles
> it's frequency. It's really fun to play around with that toy. (especially if
> you run it through a dsp based guitar processor) :)
> 
> Now I want to add amplitude control.
> 
> I thought about just building a second one, and use some kind of frequency
> to voltage converter, add a vca and have amplitude control (or filter cutoff
> controll or whatever comes into my sick mind..)
> 
> The circuit outputs a nice 9V squarewave (50% duty cycle).. any ideas how to
> get that into a frequency dependent voltage cheap?
> 
> The only idea I have is to use a moderate lowpass behind the output, add a
> full wave rectifier and then plug that into a high q lowpass (5hz, 18db or
> so).
> 
> That's just a naive idea.. would that work?
> 
> Thanks,
>     Nils Pipenbrinck