Educational electronics kits like the one from Minty Geek are a great introduction to the world of circuit building and electronic tinkering, but are perhaps a little too basic for more advanced hobbyists. Three MIT students are currently enjoying enormous success on the Kickstarter crowd-funding platform with a DIY Tesla coil kit called oneTesla that can make artificial lightning sing ... well, erm, play music from a MIDI source. Now where did I put that polyphonic version of This Town Ain't Big Enough For Both Of Us by Sparks?
The first version of oneTesla, which didn't play music, was created over the course of three days in February last year. The development team of full-time MIT students Bayley Wang, Heidi Baumgartner and Daniel Kramnik added a MIDI controller a little later, followed soon after by the hatching of plans to obtain some boards, build a few coils and offer a limited number of self-build kits on eBay to help recoup development costs. A user manual was written, revised, written again, and remains in a state of flux until the end of the current Kickstarter campaign.
The 10-inch (25.4-cm) tall musical Tesla coil was designed as an educational development kit for high voltage tinkerers with a steady soldering hand and a patient eye for precision. The creators say that building a Tesla coil will facilitate learning about wireless power transfer, high voltage electronics and radio frequency engineering. The team also advises that oneTesla is not for beginners, so those ordering a kit should have prior experience of electronics kits and troubleshooting. Although not essential, having an oscilloscope on hand for troubleshooting purposes is recommended.
Recipients of a oneTesla kit essentially get shipped some PCBs and a bag of parts that will need to be assembled and soldered together as per the supplied instructions. Each device is made up of a driver board that sits inside the laser cut acrylic main chassis and powers the whole Tesla coil. There's a MIDI input for connecting the device to a keyboard and playing live sparky music, or the supplied USB-to-MIDI adapter can be used to feed in pre-recorded MIDI files from a computer.
Although snaps/pulses from the streamer normally resonate at 220 kHz (way beyond the range of human hearing), the boffins at oneTesla have built a custom interrupter that modulates the electric arc, creating pressure waves that sound like musical notes. Sparks turned on and off at a frequency of about 262 Hz, for example, sound like a middle C. The reported maximum pulsewidth ranges run from 50µS (at 1 kHz) to 150µS (at 50 Hz) with a maximum duty cycle of five percent. The interrupter board also serves to isolate the high voltage from connected electronics.
The primary coil features six turns of thick 14AWG wire, is directly connected to the main control board and sits at the base of the secondary coil. The secondary coil has 1,800 turns of fine 36AWG wire and is topped by a toroid topload, which together form a resonant circuit that can build up to high voltages. oneTesla reports that the coil is capable of producing lightning arcs nearly two feet (0.6 meters) long. The best recorded spark length so far is 23 inches (58 cm).
Naturally, safety is paramount in a build of this sort.
"The Tesla coil poses many hazards, and taking safety precautions are an absolute must," says oneTesla. "The hazards can be lessened by being a careful worker, keeping a workspace clear of clutter, wearing safety glasses when the board is energized, ensuring that the capacitors are discharged before attempting work on the board, keeping sensitive electronics and flammable objects away from the coil when it’s running, and generally being intimately aware of the operation and hazards of the Tesla coil."
Full build and operation instructions appear in the user manual, and those who undertake the project can expect to spend a full day putting oneTesla together. A quality soldering iron, a screwdriver, some wire cutter, diagonal cutter, needlenose pliers, a crimp tool/large pliers and a glue gun (or superglue) will also be needed. The team advises making full use of the supplied ear plugs, as the coil is very loud.
oneTesla's work is licensed under the GNU GPL/FDL open source licenses, giving hobbyists the chance to reproduce and even improve on the existing designs, so long as the license is propagated.
As we go to press, although the funding campaign is set to run until January 24, all of the kits scheduled for production have been snapped up so readers interested in ordering a music-making Tesla coil build kit will have to check the team's website for updates on future availability.
Source: oneTesla, Kickstarter page
Notice that there is very little low frequency output??