This little circuit is based on an idea from Nicolas Collins’ book “Handmade Electronics”. Essentially he uses a digital inverter (that turns a 1 into a 0 and a 0 into a 1 – AKA a “not” gate) to make a square wave oscillator. I took this simple idea and altered it so that it included two resistors and two switches, so that it would oscillate at different frequencies depending on which switch I pressed. In other words, its an extremely basic keyboard synthesiser (with only two notes, and only one setting). By adding more resistors and switches I could essentially have a whole keyboard full of notes. Why, you ask? Admittedly much better synthesisers and keyboards already exist, but the process is still interesting and helps me to better understand how these things work.
Have a look at the video:
Interestingly, pressing both switches down together makes a third note. This is because the two resistors are now working in parallel with one another, causing a third resistance and therefore a third note. In order to stop this effect I would have have to make one cut out when the other is playing, or have polyphony, both of which would require more complex circuits. Perhaps this could be the next thing to work on.