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.

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!

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)

Schematic (Panel)

Stripboard layout

Stripboard layout (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.