2017-01-20 (F) Weekly Summary

Last weekend Tim described the brain chemical acetylcholine and how it related to hacking learning and memory. There were a lot more technical terms in that show than most previous shows.

Brian - Left. Tim - Right.

Long wooden keys were revised to be closer to actual piano key dimensions. The weighting from such slender pieces was difficult to make them return to a resting position without springs.

Slender wood keys

Working with the thin wood was expensive and didn't provide enough benefit. The purpose of the instrument was never to appeal to professional pianists so less expensive wood was chosen. Wider keys seemed acceptable since they still looked like piano keys even if they were a chunkier version.

Using gravity return on some of the piano keys

A huge revision to the project happened when the decision was made to use arcade buttons instead of keys. This change was made after talking to someone who works closely with kids in music therapy. Since the shape of the switches wasn't important rugged arcade buttons seemed like a good choice. They are readily available, easily replaceable by untrained people, inexpensive and meant to take a lot of abuse.

A CAD drawing was made with the layout for a single octave then printed four times. Four octaves worth of arcade buttons came to nearly four feet (1.3m). White and black buttons could be used to make it clear that a piano sound would come out of the device when the buttons were pressed although this was merely a matter of style on my part more than functionality.

Marking the center holes from the CAD print

The holes were drilled to arcade button size in a piece of 1x6 lumber and a piece of plastic long enough to cover all the buttons. Plastic was purchased locally from a surplus store. Presumably, the plastic was HDPE (High-Density PolyEthylene). Covering the wood with plastic was to prevent slivers and give it a clean look to match the plastic buttons.

Drilled wood and plastic

Programming for the Raspberry Pi Zeros was done awhile ago and tested with simple tactile switches. It would have been possible to solder each arcade button to the Pi itself but an adapter board seemed like a cleaner option. This way a replacement Pi could be installed by anyone capable of soldering a 2x20 header strip to the board and probably by just using a computer from the full-fledged line of Raspberry Pis.

Raspberry Pi Zero installed on an adapter board made for the Tough PiAno

After the adapter board was made the testing was very troublesome. The notes would not stop playing. Nothing was done to ground the wires so they were all "floating" and highly prone to interference. A short video was taken to demonstrate the effects of floating wires.

Video demonstration of floating signal wires

A revision to the adapter board would be necessary. The first testing was done with short wires so floating wires were less of an issue but long wires each acted as an antenna.

A diagram was sketched which linked each of the Raspberry Pi Zero's pins to the correct arcade button. The switches were still drawn as piano keys for clarity. Pins for the octave selector wheel were also drawn.

Old testing board and key schematic

Pull-down resistors were added to the first board wherever they could fit. It was not a clean solution but the solder joints were thick enough to keep things in place. The next three copies of the board, one for each octave, would have the resistors taken into account before constructing.

Resistor haphazardly connected to adapter board

When the resistors were installed the board was mounted in the middle of one octave in the Tough PiAno. All the wires were trimmed and terminals were crimped to each end. The wire colors were arbitrary but recorded on the schematic sheet so they could be duplicated in the rest of the octaves. Switches were taken from stock so they don't match.

Switches wired in place

Testing was done on the adapter board by connecting a Raspberry Pi Zero with the Tough PiAno software running. Some of the switches performed unreliably so hopefully the switches that were ordered are all functional when they arrive.

One octave of buttons in wood

A wooden base was built on three sides. The base will give everything room on the inside. It will be held to a wooden shelf underneath by using bolts from the underside which will couple into threaded wood inserts.

Wooden base built around button board


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