Finally, after a month of waiting for the mail due to Covid-19 restrictions, my Bela arrived. I was made aware of this project by Robert, who has already started experimenting with the Bela. The Bela is a cape (what would be known as a ‘Shield’ in the Arduino world), that expands the BeagleBone Black (a micro computer running Linux), with an extra hardware interface dedicated to ultra-fast analog signal processing, in particular sound. It distinguishes it from other micro-computer / sensor-processing / development projects by its insanely small latency of 0.5 ms. It’s dedication to sound and music that can be seen in their library, and support for C/C++, Pure Data and Super Collider. Bela was born in the Augmented Instruments Laboratory, in the Centre for Digital Music at Queen Mary University of London. Bela is now developed and produced by Augmented Instruments Ltd in London, UK. From their website:
Bela is an embedded computing platform for creating beautifully responsive interactive applications. Bela provides ultra-low latency, high quality audio, analog and digital I/O in a tiny self-contained package that can be easily embedded. Built upon the BeagleBone family of open-source embedded computers, Bela combines the processing power of an embedded computer with the timing precision and connectivity of a microcontroller.
In addition, the people at Bela provide Pepper: a PCB, faceplate and build instruction to fit the Bela and Beagleboard in a Eurorack format, using a standard Eurorack power supply, and providing input connections for control voltages with attenuating knobs, optional gate/trigger inputs, 8 control voltage outs and an 8-segment LED bar for some minimalist visual feedback. This is in addition to stereo audio in, and stereo audio out. The Bela will bring a lot of power and potential for creative integration into modular Eurorack systems for our EEGsynth project.
I was able to source all the components from RS online, and the cool people at Error Instruments for the Thonkiconn jack connectors when Thonk itself had to close their shop for a while. I’m only missing red Verbos-style Rogan knobs that I want to add, which I’ll order from Thonk now they started up again. The costs were about 120 Euro for Beagleboard, 120 Euro for Bela cape, Pepper PCB, and Pepper faceplate and components.
The PCB was comfortable to solder, with clear instructions. It was all finished in a long afternoon, and when I turned on the Eurorack power supply no smoke appeared, but some calming flickering blue lights from the Beagleboard. So far, so good!
The Beagleboard’s OS that is flashed on its own eMMC memory is not compatible with the Bela, and it will boot from its eMMC rather than the SD card with the Bela image. To solve this, the eMMC has to be reflashed with a Bela image, or disabled, as described under “Booting Problems” here. I used the third option described there. I did also create some problems for myself by removing corrupting my SD card, and then removing all partitions (note to self: use AOMEI). Finally, after quite a bit of debugging I found out that 1) I forgot some soldering points on one of the bridges, and 2) you really need all those jumpers to set the analogue inputs to take the current through the pods, including the outer line of jumpers marked ‘analog’, as you can seen in the last picture of the gallery above, and 3) if you place the whole Beagle-board + Bela + Pepper straight up it will stand pretty stable and proud on its own. However, it will also exactly lean on the micro SD card which it will then unlock and slide back and forth into its sleeve. It can take a while until you understand the buggy behavior that causes…
After that was all solved, everything was running as expected and I was able to edit and upload a little Pure Data patch. I’ll have to wait until I can mount it in a case as I didn’t yet order the extensions to break out the USB connectors, which will now arrive in a month from Amazon (here, here and here). You’ll need the connectors to be at an angle to hopefully just fit the case. I’ll probably drill some holes in my mini Doepfer case to mount them, until I figure out where to laser cut a nice aluminium front panel. In the end I expect to connect the USB host connector to my computer for development, but also connect a Novation Launchpad I have laying around to get more tactile inputs and visual feedback.