We love looking in on [Simon Inns'] projects, and this must be one of his very best. This is the fifth version of his MIDI-capable stylophone. The gist of the control system is that a conductive keyboard (made of a tinned PCB) is played by making a connection with the tip of a wired stylus — hence the name. The idea comes from the original 1968 Dubreq Stylophone hardware, but [Simon's] not just using the idea. He has his own working original and used it to reverse engineer the circuit design.
When it first came out, the Stylophone had three flavors for Bass, Standard, and Treble audio ranges. They differed only in the choices of passive components used in the circuit. [Simon] built the variations into his design so that they are selectable on one unit. This most recent version connects via USB, allowing you to control MIDI software. But unlike his first four iterations, this also offers MIDI-In capabilities. This makes it possible to control tuning, vibrato, and to drive the Stylophone circuitry from the computer interface. Get a good look at that, and a nostalgic Portal moment, by watching the clip after the break.
If you’re looking for an easier build, you might try this analog standalone version of the Stylophone.