What is the potential for PIC-based effect pedals?

[Jumbosize]

I"m really sorry if this has been asked (and I'm sure it has), but what exactly can you make, guitar pedal wise, using pic controllers? I have a decent amount of experience in coding for pic micro-controllers and I also have a fair amount of experience in building analog guitar effect pedals. I have never really even considered combining the two mediums. My question is what can be made? I have heard of delay pedals being made with pics, but is there more potential? Can distortion pedals be made? Modulation pedals like chorus/flanger/phaser? Also where can I learn more about the effect pedal side of pic programming?

[cloudscapes]

Depends on the PIC.

8bit PICs, as an LFO/ADSR source, as some kind of voltage control on analog circuitry, as preset/button management absolutely! It'll even handle being a bitcrusher/samplerate reducer effect. But while basic lo-fi samplers have been made with 8bit micros, they're very limited and lo-fi. Telephone quality, maximum. And at least as hissy.

16bit PICs, like dsPIC can probably do most of what you're after, within reason. Delays and samplers/loopers shouldn't be a problem as long as you're not doing complex tape/tube sims like Strymon does. I'm sure certain kinds of distortions are possible too, though I'm not very knowledgable. A chorus is basically a very short delay with an LFO on the delay time. Don't know much about flangers or phasers though. They might need a faster DSP though I'm really not sure.

32bit PICs, like the PIC32. I'm currently using them to make a looper and also something else sound/sampler/grain based. I doubt much of anything would be a problem on these, unless, again, you're doing complex tape/tube/acoustic simulations.

[ElectricDruid]

+1 what Cloudscapes said.

8-bit PICs are best used for control functions. I've done a lot of LFO and modulation type stuff with them. Obviously you get the digital advantages over analog LFOs; you can have any waveshape you want, you can generate random waveforms, you can do sequences, you can add tap tempo, etc etc.
The Tap Tempo Tremolo project here on DIYSB, for example:

http://www.diystompboxes.com/smfforum/index.php?topic=76436.0

This uses the PWM to drive an LED in a standard optical trem. The nice thing is the audio path is all analog, but you get all the benefits of digital.

The PWM module also makes a PWM phaser an appealing idea. You can put the LFO and the PWM generation all in one chip in software, and then use it to drive the typical PWM audio path. Like the tremolo, this would have an entirely analog audio path, with digital control.

If you want to do full digital audio processing, I'd go for a dsPIC. These are 16-bit, and several have a handy codec interface. Seb Francis has done some cool stuff with them (a quad flanging delay, for one!):

http://burnit.co.uk/sdiy/index.php?page=4xd

MIDI functions or control would be another good application for 8-bit PICs. The UART makes this easy. How about adding MIDI send/receive so you can record your tweaks into the computer?

HTH,
Tom

[Processaurus]

Tom's Tap LFO is an inspirational example of what's possible for DIY'ers who delve into programming.  I'm just getting started learning microchip assembly code but am excited about the prospects of designing things like that, as well as switching logic, adding MIDI control to things, and using digi-pots to make analog circuits have presets, like the programmable sansamp pedals.  Have you seen the Molten Voltage system Small Bear quietly started selling?  It's pretty amazing, no idea why there hasn't been more fanfare, maybe people are waiting for a paint by numbers design.  I think something like a Zvex fuzz factory with digipots for the 5 knobs and 4 presets or something would be the bee's knees.

http://www.pedalsync.com/

Sounds really cool to make a PWM phaser, because you could make a large number of low noise, matched all pass filters easily with CMOS analog switches.

[MoltenVoltage]

Thanks for the plug Ben.

I've kept things very low key for a couple years while perfecting the PedalSync line of chips and getting all the datasheets together.  I also agree most people want paint by numbers - which will be available pretty soon.

The big news is the introduction of our Hi-V digipot which can go up to 18 volts and 5mA and is a direct replacement for an analog pot in many situations.  Right now we have only 100K but that makes it easy to make a Programmable RAT or Big Muff (both of which I've done - the RAT was a straight up replacement, and the Big Muff just needed a .22uF cap in series at the center lug of the sustain pot).  The Hi-V pots can also be bridged for lower pot values or daisy-chained for larger ones.  I also made a Programmable Blue Box and DynaComp, but haven't had a chance to tackle the Fuzz Factory...

The other item DIY'ers would probably be interested in is the 9 Switches Module to make your own programmable pedalboard.

I think most gutiarists and builders hear the word "MIDI" and run for the door, but the PedalSync chips just use the Program Change and MIDI Clock, so it's dead simple to use.

Smallbear sells some of what we offer, and Steve has been good about ramping things up.  We have a new parts site too, that just lauched a week ago that has all our chips and modules:
http://www.kaom.com/