GaterAid: A DIY MIDI Rhythm Sequencer

Hey there! Welcome to the first new gadget write-up to hit this blog in 2018!

By far the best way to get your head around what this thing is and does – watch this short video.

Project history

This project has been almost a year in the making, but it had a life prior to my picking up a soldering iron – this gadget started as an Ableton Live device which I wrote a couple of years ago using Max4Live.

gaterade

The basic principle of it is really simple. The device sits in the MIDI chain between, say, a keyboard and a MIDI instrument such as a synth. When you play a note on the keyboard, the pitch of the note is read by the gadget and passed to the instrument; however, instead of just using the note-on and note-off message generated by you pressing and releasing the key, it applies a rhythmic sequence of note-on and note-off messages, as specified using the step buttons. I briefly demoed the software device in this video from last year:

So, how did this end up as a hardware gadget?

Well, I’ve been on a long mission to reduce the role that my laptop plays in my live rig (the ultimate aim is remove it completely). Replacing soft-synths with hardware is relatively straightforward (if costly) and software effects are easily replaced with hardware counterparts. I’ve been tackling the trickier areas one-at-a-time, building DIY solutions to them; regular readers will have seen the results of my efforts with MIDI clock and MIDI routing. Obviously, replacing DIY software with DIY hardware is a slightly different challenge – I already know how it should work, which is a bonus, but it’s also far less likely that someone’s already solved the problems for me (as I invented the problems).

The first step to solving this was when, browsing through the Adafruit website, I came across the Trellis keypad and LED driver. 4×4 button pad with LED backlights? Works with Arduino? Perfect! That’s half the solution right there!

1616-00

The rest was largely a case of the usual process – code, debug, breadboard, debug. Some parts of the build, such as working with a rotary encoder and LED display I already had some experience with and was able to crib appropriately. This is definitely the most complex thing I’ve made.

Making it pretty

After I’d gotten as far as having a working project on stripboard, I found that I had a need to get it into service pretty much straight away – so there then followed a period of several months where it lived in a disposable plastic takeaway box… (if you look closely at the video from TEDx Leamington, you’ll find it’s in my rig). I finally found some time to finish this project off properly after New Year.

Notes on parts

I ultimately managed to fit the whole thing into a Hammond 1590 aluminium enclosure, but it was tight and found I had to leave out the footswitch jack (JK3 in the schematic, which is optional anyway). The cutting guide and panel label below assume that the same enclosure is used.

I used 7mm tactile switches for the Read and Write buttons, which as you can see in the above images were put on their own sub-board and hot-glued into place. Any momentary push-button would do, though.

I used this 7-segment display module and this rotary encoder.

Next steps?

I’m really pleased with this gadget as, once again, I designed it from scratch – and it works well!

Moving forward, I think I’ll be taking this a little further:

  • Re-working it as a Eurorack module
  • Replacing the (expensive) Adafruit component with something lighter and more cost-effective
  • Making it work with analog clock in addition to MIDI clock
  • Making it output an analog CV gate

Build Documents

Schematic (Board)

GaterAid Schematic - Board

Schematic (Panel)

GaterAid Schematic - Panel

Stripboard layout

GaterAid Board

Stripboard layout (flipped)

GaterAid Board Flipped

BOM

Arduino Source Code

My panel design and cutting guide are available below as 600dpi PDF files. There’s also a cutting template for the cardboard baffle that I use to hide the gaps in the Trellis keypad.

GaterAid-Panel

GaterAid-Cutting-Guide

baffle

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