The Kyub is a maker friendly, open source MIDI (musical instrument device interface) keyboard that provides a new window to musical performance. Capacitive sensing gives the Kyub extremely sensitive action and an internal accelerometer allows the volume of each note to be precisely controlled for versatile musical expression. Multiple Kyubs can be attached to a computer synthesizer or digital audio workstation for solo play, jamming with friends, or composition.
The Ardunio provides an output switching between zero and five volts at high speed and connected to all pads through separate large resistors (1 megaohms). The touchpad acts a bit like a bucket and the resistor like a constriction in a hose that fills the bucket (five volts) and drains the bucket (zero volts). This voltage is monitored at a different Arduino input for each pad.
When no one is touching the pad, the effective "bucket" size is relatively small and there is a only short delay between the time when the square wave rises to five volts and a logical high state (somewhat less than five volts) is detected at the input of the Arduino for that pad. When the pad is touched, the bucket size increases (you become part of the bucket) and the delay increases substantially. By monitoring the delay with an internal clock, a touch is detected.
When a touch is detected a recording of the acceleration from the accelerometer is reviewed a little bit before the touch and a little bit after the touch (the window) using a rolling buffer (like an endless loop tape recorder). The peak value of acceleration within this window is used to decide on the volume of the note. The pitch of the note is determined by the particular pad being touched. These two pieces of information are bundled together and sent out in the form of a MIDI message to the synthesizer. Only the axis of the accelerometer corresponding to the orientation of the pad is reviewed.
Video of extended performance
Here is a shot of the printed circuit board sheild with the accelerometer breakout board from Adafruit positioned in the center on a socket and standoff.
The inside wiring is a bit of a nightmare but fortunately you only have to do it once and then it safely packaged inside. Jumper connectors from Adafruit make this a bit more forgiving. Shield is positioned on the Arduino, the latter bolted to the bottom of the box.
This version has epoxied brass pads on the outside cut from a strip of hobby brass
Soldering brass tabs on the back allow later connection of wires to the pads after the epoxy has essentially covered the other surfaces
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