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Music as output from Interrupter (optical to audio)

PostPosted: Sat May 23, 2015 11:14 am
by tonymudd
Has anyone worked out a circuit for turning the optical output from an interrupter into audio?
I'd imagine something fairly simple - transistor or 2, couple of resistors (to limit input and output) a photo diode or transistor and a loudspeaker. It would be useful to be able to hear the output to test the midi files or conversion of.

Re: Music as output from Interrupter (optical to audio)

PostPosted: Wed Jul 31, 2019 2:51 am
by dmicek
Yes, I wanted the same thing and just figured it out today. I used a passive speaker that came with my arduino kit. You could probably use earbuds too. Put the positive lead on PIN 4 of the ATMega. The negative lead to ground. (touch the neg lead to nearby solder points until you find one that generates sound) You can find the interrupter board schematics in the download section of The sound is faint without amplification, but you can clearly hear the song. The resolution is low because the pulses are on/off square waves at specific frequencies. The higher the frequency of the pulses, the higher the pitch. Came in very handy to test a midi file I was working on without having to run it through the coil.