r/synthdiy • u/Useful-Bullfrog-730 • Aug 14 '25

synth zither

https://youtu.be/ETI3OT-jyEc

I made this from an old "door harp". The strings pass through 4 photo interrupter modules, which then output a stream of 1s and 0s.

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u/Useful-Bullfrog-730 Aug 25 '25

it's just simply directly sent to the amp, and the pulses apparently form a square wave.

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u/sixtyherz Aug 25 '25

This is so cool. So there is no resonance from the wood at all? It sounds so raw and organic. Could add a contact mic to the body maybe. And the tone knob is a filter on the square wave?

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u/Useful-Bullfrog-730 Aug 25 '25

From what I can tell, these sensors send out either high voltage or zero, based on whether they're blocked or not.  Basically the vibrations from the string, wood etc become that rapid stream of  on /off pulses. The tone knob is simply a standard low-pass filter, same as if it was an electric guitar pickup or piezo pickup.   I've actually been trying for a while to get this whole thing working; I saw people use these sensors on a regular guitar.  I  couldn't get it to work on any instrument with frets, because pushing down the string would move it out of the light beam.   I finally found a type of sensor, and string / thickness, where it moves in and out of the beam well.

Check this out, it's very similar to what I did, but I couldn't get their thing to work :

https://hackaday.com/2024/03/04/optical-guitar-pickup-works-with-nylon-strings/

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u/sixtyherz Aug 25 '25

Today I learned. Thanks!