Capacitive touch sensors gain fans - EMS in EDN

click here for the full article on EDN.
"The product of Russian-government-sponsored research into proximity sensors, the Theremin sensor, which Leonard Theremin invented in 1919, represents possibly the first commercial use of capacitive sensing. The device senses the proximity of a musician's hands to a pair of antennas that modulate the frequency and amplitude of two heterodyning oscillators that form the heart of the world's first electronic music synthesizer. Continuing this theme, in 1972, designer David Cockerell at Electronic Music Studios penned the KS keyboard as a sequencer for the company's range of voltage-controlled synthesizers (Reference 1). This intriguing device boasts a 30-note, touch-sensitive keyboard whose inputs rely on the TTL characteristics of two 74150 16-to-one-line multiplexers. These devices scan the keyboard, taking their clock inputs from a 4-bit binary ripple counter. A network biases the inputs to the multiplexers to hold them close to their switching threshold, which a finger press then exceeds. At this time, the appropriate data-selector output goes low to latch the 4-bit code and the multiplexer's identity to create a 5-bit address that represents key position."
via Paul Perry of Frostwave on the sdiy list.