Homemade Hardware – Final
For my Homemade Hardware final, I decided to continue and pressure the keyboard design. The keyboard itself, is highly influenced by the Roli Seaboard and it’s approach towards multidimensional midi controllers, but rather then an expansive, software specific solution, I wanted to make a ‘cheap-as-possible’ multidimensional midi keyboard controller.
I started prototyping the idea of how the keyboard would actually function and ended up using a dual sensor setup for each key, where the pressure is determined by an FSR (force sensing resistor) sitting at the bottom of each key, and your finger position is determined by a soft-pot at the top.
Once everything was working on the breadboard, I moved to Eagle to start designing the board that would read the sensors, and send them over serial to the Raspberri Pi, which would function as the synth, turning the data into either sound/midi commands sent to the computer.
Bill of materials:
- Atmega328 micro controller
- 2x 4051 multiplexers
- 16mhz resonator
- resistors, capacitors and header pins
I created two boards, one prototype (through hole) and one final (SMD) boards. I started by laying down the parts which I would need, and position them, the two boards are near identical, just the parts (symbols) are different to match the different PCB techniques.
After making the through hole version I wasn’t able to find a 16 channel multiplexer in a surface mounted version, and so decided to use 2×8 channel multiplexers and use the same control pins, so they are chained to the same select pins coming from the micro-controller.
I started with toner transfer, which went surprisingly well. My times were:
- Run the board with the vinyl print through the laminator 5 times
- Iron each side of the board for 4 minutes, keep constant movement (I listened to dub music which really helped set the down tempo loopy mood for ironing)
After toner transfer was done I acid etched the board which took about 25 minutes for 3 boards.
After cleaning the boards from the remaining toner, I started placing the parts I would need to solder and created a solder stencil. One thing that really helped me smooth the solder stencil process was to get rid of unused pins on the Atmega328, which was quite straight forward in Illustrator.
The settings I used for the laser cutter:
- Raster mode
- Speed: 10
- Power: 15
After some more dub music, and quality time with the pick and place machine I was able to get 4 boards soldered and re-flowed. Out of 4 boards, I got 2 working ones which is A LOT compared to my previous ratio when making boards with the Othermill.
Programming was a breeze thanks to this nifty little thing, and I was able to burn the boot-loader and upload my sketch in a matter of minutes, here is the test app I uploaded
After beep testing the boards I drilled and hand soldered all the header pins in place and tested my board with a second Arduino that reads the serial out from the board, and IT WORKS!
Special thanks to Shir David for help with shooting.
I am currently working on fabrication aspects of the keyboard, such as enclosure, soft key molding and general design thing and would like to continue developing this into a functional ‘multidimensional‘ keyboard.