DI

Y

MUSIC

TV-TO-SYNTH INTERFACE

Triggering sound from video images.

By Tom Zimmerman

In 1922, a 16-year-old farm boy from Idaho sketched corder. The circuit emulates a mechanical switch, the idea for TV on his high school teacher’s black- so it can be wired to any low-voltage circuit (like board. An avid reader of science fiction (he would a remote control), allowing movement in a video have loved MAKE), Philo Farnsworth got the idea image to start a CD player or a VCR, for example. of scanning an electron beam across a phosphor screen while mowing hay fields.

Illustration by Damien Scogin

In this project, we’ll stick phototransistors to a TV screen to trigger musical notes on a synthesizer. A peak detector circuit removes the 60Hz pulses caused by Farnsworth’s scanning technique. When a bright object passes under the phototransistor, a CMOS switch closes, triggering a musical note. Any video source displayed on a CRT or LCD can be used, including movies, TV, live cameras, and computers. I originally built this circuit to generate sound from a recording of dancers that was filmed with a Fisher-Price cam-

Install a D25 Connector to a Keyboard Circuit Board

Get an inexpensive musical keyboard. Remove all the screws from the back of the keyboard and remove the case, being careful not to pull any wires loose.

Locate the cable that connects the main circuit board to the keyboard. The keys are multiplexes, so the cable should contain about a dozen wires. Prepare a D25 solder-type socket with enough wires to connect to every wire in the cable, plus two for power and ground. Using a Dremel or

Make: 123