Another class project, this time the goal was to create a twelve-note polyphonic (more than one "voice") synthesizer using the classic 555 timer IC. To conserve board space I used LM556 dual-timer ICs, however if you have the room there is no reason you couldn't use standard LM555 single timer ICs. Though David's (my professor) original final project criteria called for a "weird sound generator", I opted instead for something a little more tame, and tuned my "piano" to the twelve notes of the chromatic scale.
I will be sure to do a proper write-up for this project at some point in the near future, however for now all I've got are the schematics and an overview of the keyboard in the write-up I submitted as my final project for my ELEN146 (Semiconductor Devices) course.
The Altium project files are too much of a mess to upload at the moment (100+ files); once I'm off for the summer I'll make a concentrated effort to sort everything out and upload everything.
The PDF only shows one of the oscillator circuits, but all six are identical with the exception of two resistors, as explained in the document. I know the write-up seems long - don't worry there are lots of pictures, graphs, charts, and tables to break up the monotony.
The power amplifier can be skipped if you have a set of computer speakers you can use instead; just be sure to throw in a cap to block the DC from the 555-timers. Really any value is fine, but something above 1uF would probably be best.