Guitar synth successful build

[Mick Bailey]

I've been working on a guitar synth pedal project over the winter and its ended up being reasonably successful with fairly good note tracking and latency. It uses a Seeed XAIO RP2040 for the signal input and has an analogue filter and VCA. The Seeed is only around $5 (£5.50 in the UK) and I built the circuit on Vero board. The synth has some classic sounds, plus a harmonizer function. I used a TS271 programmable opamp for the filter, based on Raymond Shouten's development of the Polivoks filter.

Here's a clip. I don't know why, but the video quality went off when I uploaded it. I'm using a Boss DS-1 in the FX loop of the synth and DIY delay pedal on the output;

https://youtu.be/MhTZyPiJ7UM

[35L6]

Nice work !

[xtian]

Bitchin'! Can we build one, too?

[tedmich]

cool, and exclusive!

[Helmholtz]

Wonderful little machine!

[The Dude]

Nice work, Mick!

[DrGonz78]

I was thinking the whole time that I need one of those! Nice job

[Chuck H]

Cool

[pdf64]

Fantastic, well done!

[Mick Bailey]

Thanks for the comments - here are a few more sounds. There's a momentary foot switch plugged into the right hand side so that a note of chord can be held and with a bit of practice it can sound like two or more instruments. I'll put together the schematics and build notes for anyone that's interested - it's a straightforward project for anyone who's built a pedal or other piece of equipment before.

https://youtu.be/-qqAgKqKdQs

[Mark Hammer]

Oh my goodness! I have a Casio MG510 MIDI guitar, but the tracking on this kicks the 510's ass around the block. A few questions:
1) Divided pickup of some sort or just plug the guitar in as is?
2) Did you program the sounds or are these from a library of some sort?
3) What hardware would I need, in addition to the Seeed module?
4) Is this related to the Daisy Seed, or an entirely different company/product?

[Mick Bailey]

The guitar just plugs right in. No libraries are needed - the sounds are generated from fundamental waveforms - square, square/PWM, sawtooth, sawtooth + octave, sine, triangle, FM1, FM2, FM3 and output using PWM. I based the idea on Hagiwo's chord VCO which he developed from a Japanese magazine article - this is a voltage controlled modular synth oscillator that uses 1v/oct and I've expanded this for guitar. The guitar signal processing is something I've been working on for a good while using an arduino.

The different sounds come just from different waveform selections and filter + envelope settings.

Apart from regular pedal-type components and a Seeed Xaio RP2040, there are some specific parts - 3x rail-to-rail 5v opamps (I used MCP602), a reasonably fast vactrol, and a TS271 programmable opamp. I got a bunch of dip ones easily but the smd type is in current production and can be soldered onto a dip header.

I think the daisy is the same processor, but don't know if it has the 4 analogue inputs that synth needs.

I have the schematics and notes almost finished to upload tomorrow. The Seeed has an inbuilt USB and uses the free arduino IDE. No programming knowledge is required - install the IDE and Seeed board driver, load the synth file and flash the processor.

[The Dude]

I love the project, but admittedly, most of your description is gobbledygook to me. I'm just a lowly tech with zero design experience in this sort of thing. So, excuse my ignorance on the subject.
With that short preamble in mind, I'm curious. Would it be difficult to add MIDI out to such a device?

[Mick Bailey]

My original guitar interface using an Arduino Nano was capable of MIDI out with a little bit of recoding and I used the same basic code in this synth design. The snag is I used up all of the outputs on the Seeed - the small size of the postage-stamp sized board limits what you can do. There are other boards that use to same RP2040 processor that have the full complement of pins which could be used, but these are more expensive and take up a lot more space.

[Mick Bailey]

Here are the schematics, .ino code file and construction notes;