We did it. 2021 is over. L— and I went for dinner at a friend’s house, watched a strange, low budget, but very enjoyable comedy horror film (Tucker & Dale vs Evil), and went out to the river to watch the fireworks and light shows at midnight.

Some people call the period between Christmas and New Year “Twixtmas”, but I heard an alternative on the radio this week which I like more: the Winterregnum.

We went up to L—’s brother’s house to spend the afternoon with their parents and her brother’s family. We ate some food, played some games with the children, and I had a great time. The government making it illegal to meet people has really renewed my appreciation for just socialising.

But what did I do with my time off? I’ve been working on a generic digital Eurorack module using a Seeeduino XIAO microcontroller board, after seeing a couple of projects posted by a Japanese engineer who goes by the pseudonym of HAGIWO.

They’ve posted a couple of projects that take advantage of the 10-bit DAC on the XIAO to generate audio: a drum sample player and a VCO. 10 bits isn’t hifi, but it’s not as bad as all that, and it has a character of its own.

The Seeeduino XIAO is available for about $8/piece, and it’s pretty capable. On top of the DAC, it also has a quarter MB of flash memory, a 48MHz ARM Cortex M0+ processor, and 11 pins that can each be assigned as 12-bit analogue or digital inputs with interrupts, or as outputs. And you can program it over a USB-C connection.

What I’m putting together is a generic module that can be programmed for different tasks. It has:

  • 4 knobs
  • 2 CV inputs
  • 1 V/octave pitch input (can also be treated as a trigger or gate input)
  • 1 DC-coupled output
  • 1 LED (brightness controllable via PWM, possibly, if it’s not too noisy)

and it’s all packaged into a 4hp (20mm) wide two-board sandwich.

Depending on programming, it could be:

  • a 2D wavetable oscillator with X and Y inputs on CV1 and CV2
  • a drum voice
  • an ADSR envelope with attack and decay on CV1 and CV2
  • a drone oscillator
  • a complex LFO

To make my life easier, the 5V supply to the XIAO is through a jumper that can be removed to allow it to be connected to USB and Eurorack power at the same time. I hope that this will allow me program and calibrate it more easily.

My plan is to get a batch of circuit boards made and assembled with most of the components, which seems like it should cost me under £30 for 10, finish off the assembly myself, and assign them various roles. A lot of people get their front panels made as PCBs, and I was tempted to do the same until I discovered Meface, a company in Bury St Edmunds that does one-off proper aluminium Eurorack panels at extremely reasonable prices. I’ll let you know how that goes.

I’ve been designing the circuit boards in Kicad 6. It’s a fun puzzle (for me, anyway) to try to route everything efficiently, stopping occasionally to reassign pins to avoid unnecessary crossing. I’m getting faster at it, but I can still get absorbed in it for hours. That’s not good for my bedtime, but it’s great for my mental health, leaving me no time to look at the news!

Getting back to a normal routine on Tuesday is going to be hard.

This marks a full calendar year of weeknotes. What do I do next? Restart at Week 1, or keep going?