Earlier this week, the fully re-designed revision B PCBs have arrived from @oshpark, and they are even more beautiful than I imagined. You simply cannot emulate this shininess in KiCad's 3D Viewer ..or capture it on a picture, but here is one nonetheless:
The main change is obviously the PCB shape. I honestly don't know why I thought a MIDI keyboard had to be credit card sized in the first place, it's not like you'd carry it around in your wallet along with a battery powered computer to actually use it. So I figured, why not give it a more musicy look.
Also there were a few issues I didn't like in my initial design and wanted to change regarding the crystal oscillator (too high frequency for 3.3V supply voltage and a form factor which wasn't that easy to source) and the LCD (also sourcing situation, couldn't fit the back light, and they kinda kept on dying on me). Also the horizontal button arrangement for the chords playback didn't feel very ergonomic or natural.
So with the new boards designed, manufactured, and right in front of me, last night was the time to turn one of them into a functional prototype:
I emphasize prototype here, because I realized a few things along the way:
- There's really no need to have zero Ohm links in the power supply paths, this is a USB powered device. While analyzing and optimizing current consumption is fun and interesting, there simply is no reason to be able to do that in the final design.
- Real pianos may be nicely balanced with three legs, but they don't have a huge USB connector in their upper end either. Pressing the "<" button will topple the board with the current mechanical arrangements, so that will need some adjustments.
- On very first try, the LCD back light didn't turn on, and I haven't had time to look into it yet, so there is a possible issue that needs some re-work. Maybe I should just stop using BJTs and finally get more familiar with FETs.
- Edit: turns out I used the wrong generic NPN transistor in the schematic, and base and emitter ended up swapped. Removed the SOT-23 transistor, bent some legs on a TO-92 to replace it, and back light turned on just fine.
- Santa is coming early this year and he's so gonna bring some hot air soldering equipment.
So there will be another iteration in the near future taking care of all these things, and once I'm satisfied with the results, the PCB will be available from OSH Park's shared project section, and some assembled ones will make their way to Tindie. And in the mean time, I have a whole list of new feature ideas for the firmware to work on, so I won't get bored.
(Side note on Tindie, if you'd be interested to get a 4chord MIDI keyboard, drop me a message so I could get a rough picture)