[sdiy] Using audio to trigger CMOS

[Richard Johnson]

Justin,

I should be shot for even attempting to suggest. I'm only a
theoretical DIYer at the moment.  :)

Ironically, I've been heading down a very similar path as you in terms
of using a guitar pickup for triggering some very simple 9VDC
circuits.

What you might look into is using a diode and a capacitor exactly the
way an AM "crystal" radio does (really! just a diode, capacitor and a
resistor). That way the waveform of the timbre/pitch would be filtered
out and you'd be left with a curve that is the overall playing
dynamics of the pickup.

See an AM demodulator at the bottom of this page:
http://www.electronics-radio.com/articles/radio/modulation/amplitude_modulation/am.php

Once you have that, you should be able to use a 555 timer, op-amp,
comparator or really any adujstable-threshold Schmitt trigger circuit
to find the "plucks" of the string. Make sure that whatever you do,
there's a "Schmitt" element to keep from getting a mess of Note Ons at
each pluck of the string.

LIST: Feel free to smack me down. :)

Ric

On Mon, Apr 28, 2008 at 5:18 PM, Justin Owen <juzowen at googlemail.com> wrote:
> Thanks to everyone that's chipped in on this - much appreciated.
>
>  I think the first - and maybe the biggest - problem is getting enough gain from the input signal. I was hoping to get this running on a 9 volt single supply - and it seems like the most I've been able to coax out of an op-amp configured as an AC Coupled inverting gain stage is just under 1 volt of gain - so basically 0.01 volts at Note Off and just under 1 volt at Note On.
>
>  I did look at some Envelope Follower schems (and the Polyfusion schem has given me some clues) - but I was hoping for something alot simpler as this really just needs to convert a particular type of audio signal into a gate/trigger. (Although maybe I've underestimated how simple this should be...)
>
>  Roy and Anthony's suggestion about using a Hex Inverter in Linear mode is cool - will try that and see what goes.
>
>  Paul - Your suggestion about using a 555 one shot was also v. helpful - but it would mean re-jigging the way I have the rest of the clock set up - so at the moment, I'd like to try and solve this current set of problems. Always good to have a Plan B.
>
>  Harry - Yeah, Ideally I'm looking to get Note On and Note Off (pitch doesn't matter - it's the timing/on/off part I need)
>
>  Since I'm still a little stumped on this - any more input would surely be welcomed.
>
>  Thanks again to those who've helped out.
>
>
>
>  J
>
>
>
>
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