Around the time of their first album, I played a bunch of live shows with the Oryx and Crake. The band combines a variety of sounds, from orchestral instruments to electronics. I pitched in on some of the electronics, including building unique MIDI instruments to use live. The instruments were constructed from salvaged goods and devices, old and new, from thrift stores and piles of e-waste. Here are my favorites.
A sensor salvaged from an inkjet printer is attached to the crank on a manual coffee grinder. Turning the crank faster changes the pitch and density of a rhythm (independent of tempo). Turning the crank backwards controls a different rhythm. Here's a little demo:
Embroidery hoops, a laptop keyboard, and a foot pedal from a sewing machine form an instrument that makes whale sounds by rocking the hoops back and forth, and crashing waves by stepping on the pedal.
An old hard drive is opened up, exposing the spinning platters. Turning the discs manually, like a miniature turntable, scrubs through a sample using granular synthesis. Unlike scratching a record, this can hold a moment in a sample, or move through it at any rate, independent of pitch. In this case, a sample of a baby crying is stretched into an endless wail.
The granular synth was made from scratch in Max/MSP. It's pretty crude, but a nice fit for this application.
An alarm clock, guitar pegs, and a door knob, become a general-purpose MIDI controller for fine-tuning control changes.