Musical Tesla Coils…

by Stephen Hobley on March 30, 2009

…and I guess I use that term lightly.

I’ve been building a MIDI modulator for the DRSSTC tesla coil I put together last year.

One of the problems is tuning a 555 based oscillater to match MIDI note numbers. I played around with Excel for a while, but couldn’t really get anything useful going. So I wrote something in C# to help.

555 to MIDI calculator

555 to MIDI calculator

This application calculates the frequency of a standard 555 timer in Astable mode based on the values of C, R1 and R2. I split R2 into a fixed resistance (R2a) and a variable resistance (R2b). R2b is controlled via the MCP42100 digital potentiometer that can be hooked up to an Atmel microprocessor very easily.

After calculating a set of frequencies for the 555 timer, it then goes on to calculate the set of frequencies for standard MIDI note numbers.

Finally it compares the legal MIDI note numbers to the table of 555 values, and comes up with the best match for each note in table 3.

I’ve not yet implemented the results in hardware to see how musical it sounds, but on paper it all seems to work well.

The application is a C# solution available here (also contains compiled runnable version).

Update; it does work!

Even thought the sound quality is very flaky – this first run shows the tuning is just about right.


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