Throughout the maker pavilion, the siren song of a musical Tesla coil could be heard. Those who followed their ears found themselves at the oneTesla booth. OneTesla is a hobby Tesla coil, with the added twist of polyphonic MIDI input.
Started by three MIT students, oneTesla had a successful Kickstarter campaign last year. Like many kickstarters, they are a bit behind in the shipping department. They are shipping out their third run of kits to backers now. The group had a small number of oneTesla coils for sale at the show, which appeared to have sold out by midday Sunday.
The actual process of generating sound with a Tesla coil is fascinating. All Tesla coils are resonant at high frequency. In oneTesla’s case, this is 220kHz. Human hearing ends around 20kHz, so this is well beyond the range of perception. Since the coil is locked in at this frequency, the power to the coil is modulated at the desired sound frequency. Playing an A note for example, would mean modulating the coil at 440Hz.
In OneTesla, all this is handled by the MIDI interrupter board. An ATMega328 performs all the heavy lifting of modulating the coil. Even more interesting is the fact that the MIDI interrupter can create two note polyphony by interleaving the modulated notes. Think persistence of vision style effects, but with audio. The interrupter also acts as the overall power control for the coil, eliminating the need for a variac on the AC side to control overall coil power.