Touch Keyboards and Step Sequencers

Aside from module renovations, I'm also planning on creating some "modular synth" style controllers. I do have a MIDI interface which works well enough, but I've always been intrigued by step sequencers and "Serge Touch Keyboard" type controllers.

I'm still very much in the brainstorming phase, but essentially, I have two projects planned - a simple 8 stage step sequencer and a capacitive touch keyboard controller (TKB). I'll have a lot more to say about these in the near future, but for now, consider this a sort of "statement of intent".

I've also started a YouTube channel to put up some video reference for these projects. So far, it's just me running my finger over the pins of a touch sensor chip and a few linked videos of devices like I'm considering. I plan to shoot a similar 10 second video of the 4-stage prototype sequencer I breadboarded over the weekend. It's also just some flashing lights at this point, with a rate controlled by a knob, but it's progress.

My sequencer is based off of a 4017 decade counter and a 555 timer. Hardly a creative and unique design, but I need something simple for my first time. I'm planning to base it off of the version in Barry Klein's book, which in addition contains some logic to support external and manual stepping controls. I'm going for a single CV output, portability and the ability to run off of a 9v supply.

The TKB is similar - this first version is 8 stages with touch-capacitive plates to activate each stage. The stages will be individually tuneable, so the keys won't correspond to piano keys, unless you tune them that way of course. So it's a very small keyboard at the moment, but I'd like to save the expense of a larger keyboard for after I've discovered what's horrible about my design.

The TKB is going to be controlled by an Arduino, since I'm better with software than hardware. The sensor I'm using is an AdaFruit CAP1189. I'd like to build some sequencing features in as well, so you can either play it like a keyboard, set it running, or both. The Korg Volcabeats is an inspiration, as is of course the Serge TKB.

A side note about the CAP1189 - it seems from the datasheet that I could use the built in LED driver hardware to trigger the key stages, as the chip can be set up to output whatever values you want from those ports instead of echoing the touch plate sensors. I had originally planned to use 74HC595 shift registers, driven by the Arduino using data pulled from the CAP1189. But if I can use the CAP1189 for both duties, then I can save some board real estate and part counts.

Sounds like a good next step for the software part of that project.