Happy with recent progress! After deciding to go for a more simple, bare-bones design, I designed a new PCB which ran off 3 AA batteries instead of 2, eliminating the need for voltage regulation. I also made the decision for the top surface of the PCB to be the actual front of the instrument, eliminating the need for a traditional case. Long story short, the PCB arrived and this is approximately what it looks like when assembled, with a few caveats to be discussed further down:
You can see that the design consists of a top and bottom layer, separated by standoffs, as well as an extra "palm rest" piece on the top layer, to cover ugly/sensitive electronics. The main circuitry is on the underside of the top PCB - the "palm rest" piece just hides the solder. There are now six buttons and four knobs on top to control the instrument, plus a volume knob. I'm really pleased with the look and feel of the instrument, but there are a number of ways in which the final version will differ from this mock-up:
- The potentiometers will be slightly shorter and knurled for better ergonomics
- The standoffs and machine screws will be metal for better durability
- The battery holder, which is mounted on the underside of the PCB, will be secured in place with machine screws and dome nuts, for better aesthetics than the current temporary nut
- In this photo, the top "palm rest" cover is 3D printed, while the bottom, protective layer of the case is actually just a spare, unpopulated PCB - both these pieces will likely end up as laser-cut plywood or acrylic
There is also one other key way in which this prototype can be improved: it doesn't actually work! I'm embarrassed to say that I was rushing to finish the PCB design before heading to Glastonbury music festival with some friends, and ended making a silly mistake which rendered the entire board unusable. I am very keen for this design to be "hackable", so I have added breakout connections for all the main Arduino pins (5V, ground, 14 digital pins, 6 analogue pins), but I was struggling slightly for space and, as far as I can tell from reviewing the KiCAD files, I must have attempted to move the breakout pins halfway through routing the board. In doing so, I created a short circuit which I only noticed when testing an assembled board. Here's what I did:
All I had to do was click the "run DRC test" button, and this mistake would have been glaringly obvious, but by this point it was midnight and my mind was focused on packing for the festival. Never mind! It was a good lesson, and there were a couple of other minor issues with the board which I noticed anyway (mounting holes in the wrong place, poor layout choices, etc), so I've created a minor revision of the board and ordered another small run of 5 PCBs from China. Fingers crossed! In the meantime I can keep working on the code/firmware using my breadboard/Arduino circuit.