Illustration by Damien Scogin


Triggering sound from video images.

By Tom Zimmerman

In 1922, a 16-year-old farm boy from Idaho sketched the idea for TV on his high school teacher’s blackboard. An avid reader of science fiction (he would have loved MAKE), Philo Farnsworth got the idea of scanning an electron beam across a phosphor screen while mowing hay fields.

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, ...

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