Tuesday, January 3, 2012

NIC Coil Project Finished

Finished the Twin Solid State Tesla Coils just a few minutes ago. Periodically working on the coils for over 8 months now I finally spent a good few hours to get the primary coils done. Everything is wired up and I have tested both coils both separately as well as together to see how they handle feedback.

H-Bridge went through two hardware revisions mostly due to cooling and space issues. The first design had an entirely different bridge which was level to the floor of the case. It used a linear regulator off a toriodial step down transformer. The second and final design used a Switch Mode Power Supply providing 12.7V which was broken up into other voltages with linear regulators to keep noise low. The control knobs also changed sides to bring them in reach of the power switch for operator safety. The driver circuit went through two hardware revisions. The first being a Duemilanove at 16MHz mounted beside a driver board. The second and final one being two stacked boards with the ATMEGA 328P running on the same PCB as the VCO at 20MHz.

The software went through five revisions in total. Rev 4 used a pulse timer system which worked but proved unreliable for audio input at frequencies above 1KHz and had a number of harmonics which it could not respond to. The final revision Rev 5 used a hybrid Zero Crossing Detector and Pulse Timing system which allowed up to 2.5KHz audio modulation while remaining completely stable and with no harmonic problems. Rev 5 also included reduced power consumption and higher noise immunity. The control system draws 30mA idle (mostly LED power consumption) to 50mA when fully active in Audio Input Mode.

Now all that is left is some tuning to get longer sparks, some cosmetic clean-up perhaps a washup and paint. To get a bit bigger sparks I plan to raise the primary coil up which should be easy as it was originally designed to do this. I reduced the primary winding to 20T from 21T which did almost nothing. The current draw of these things is 0.3A to 3.4A on the interrupter mode and 0.3A to 6.8A on the audio mode (0-2.5KHz).

That is all for now, documentation, schematics, and operators manual are next.

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