I've talked about doing this forever, so I am happy to finally be able to introduce my 95% complete, voltage controlled DOD Grunge FX-69! Frac-rack modular synths have been in my opinion missing a voltage controlled distortion module, with wave-folders being about as close as I could find. I had a torqued FX69 sitting around, and figured it would sound wonderfullyterrible in my synth setup. I'll spare you the history on all of the approaches I thought about taking to add voltage control to an old pedal, and just say that the Arduino Duemilanove along with an analog devices AD5204 I2C controlled digital pot is perfect for this. You end up with a fantastic, easy to program microcontroller with 4 analog inputs that control four 100 kohm potentiometers, and even have PWM outputs you can use for indicator LED's. This design could work for anyguitar pedal. And the how-to on the Arduino site did all of the heavy lifting for me!
To make it really functional, I used a two input version of the unipolar voltage summer from Ken Stone's CGS33 matrix mixer. I wired it to give a fixed offset voltage from one pot, and zero to unity gain on the other. I chose resistor values to divide the expected 0-10V control voltage in half (the Arduino AtoD want's 0-5V). Also added some diodes to prevent the Arduino from ever seeing negative or >5 volts. To bring input levels down, and output levels up to modular levels, I used a CGS 60 stompbox adapter circuit.
Last, I wired the stomp-pedal switch to the front panel. I'll add gate control to this someday, when I figure out what I really want from it (I left an input on the front panel called "on"). I run the Arduino off of a 10V voltage regulator (you can run it off of the USB power, or an external supply while setting it up initially). Stuffing all of the boards (including the green DOD board at the bottom) behind a 2U Frac panel took a little doing, and it isn't "finished" looking, but damn, this thing snarls! You can use the loudness input as a flavored VCA (kind of like Buchla LPG's), and coupled with a Blacet envelope follower (Input Processor IO2225), you can do things to a guitar others can only dream of! And the whole thing (less the pedal) cost substantially less than $100!
Hopefully I'll find the time to do a YouTube video soon, after my forthcoming SMS Audio Appendage video.
Next on my Arduino agenda, I want to make another sorely missing module, a midi-tempo synched LFO. Shouldn't be hard with the MIDIVOX I just picked up from the Maker's Shed.
