Anyone who’s shivered in the dark at a scary movie or laughed at the unintentional cheese-ball of a bad sci-fi (paging Ed Wood) knows the eerie sounds of the theremin. In the classic theremin design, two antennas control pitch and volume, and you play the instrument by moving your hands near the antennas without touching them.
This simpler design uses interrupted photons (light) instead of radio waves, and can be built with a handful of common components, including the versatile 555 timer chip. When we’re done, we’ll have a decent sounding mini-theremin. You can experiment with its sound by changing the type of light sensor used and the capacitance of the circuit.
Photodiodes work in this circuit, but you can get a broader range of tones by swapping in photoresistors, which RadioShack sells in a 5-pack.
Try different types of photoresisor, and also try removing one of the 0.22μF capacitors — this will alter the range of pitches you can produce.
See and hear the Light Theremin in action here and here.
The venerable 555 timer integrated circuit used in this project is the most popular IC of all time. You can learn more about it here and read about a chance encounter with the designer of the chip, Hans Carmenzind, on MAKE.
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