I am happy to report that I have finished my project with Bela Gem Stereo to create an electronic hurdy-gurdy. This is a great platform for an end-to-end hardware synthesizer. My past projects have been more midi based using Arduino, so coming to this platform which has enough power for real audio stuff is exciting.
As a hurdy-gurdy player, I wanted to see if I could create something that I could possibly use in parts of my live performances.
My goal was to have an instrument that could play an authentic sound, as well as the ability to play other sounds, with more flexibility than a hurdy-gurdy. As a first project of this kind for me, I wanted to keep things simple. Therefore I decided not to attempt a wheel. There is a project called Digigurdy that goes down the path of the actual wheel (and I might explore that direction in future).
Software features:
- 4 voice polyphonic sampler engine with looped as well as one-shot samples
- automatic cross-fade looping of looped samples
- per voice volume, attack, release, transpose
- support for different scales
- optional randomization of loop start position
Hardware features:
- keyboard: 24 melody, 6 drone keys, 1 trompette key, 1 melody toggle key
- 5 buttons and one rotary encoder for menu navigation
- 16x monochrome screen
- 1 mono 1/4 inch output
The most time consuming part was building the keyboard. I used kailh choc v2 low profile keys with blank key caps mounted on perf board. This allowed me to solder to the perf board rather than the keys. These were mounted to acrylic sheets. To handle 32 keys, I used two MCP23017 chips which were connected to the I2C bus on the Bela. The interrupt pins were ganged and connected to a Bela gpio pin. The 16x2 screen was also connected to the I2C bus.
The encoder and the other buttons were connected directly to GPIO pins. The 1/4 audio jack was connected directly to the line out with two pins (unbalanced).
The other component I used was a USB-C extender cable with a thru mount which allowed me to have a direct USB-C port on the exterior to avoid wear and tear on the Bela usb port. I also got a 20000 mAH power bank which right now is external to the enclosure (and I might keep it that way).
The other challenge I ran into was connecting 32 wires to the 32 inputs on the MCP chips as well as connecting the wires to the GPIO inputs. Thanks to @giuliomoro for the tip on this, I was able to solder all wires to small strips of perfboard with pin headers and just plug all in together.
I did some detailed sampling of one of my hurdy-gurdys to get each sample (of about 2 seconds in length). I did do some repitching of the low and high samples so that I could extend the keyboard when transposing up or down. In addition to hurdy-gurdy samples, I have also created sound banks using saw and sin samples, and plan to record other banks for other sounds from bagpipe, Indian harmonium, flute, etc.
