Sunday, November 28, 2010

NIC Solid State Tesla Coil Project Update 3

I have had very little free time to work on the coils lately. Started thinking about the control board circuitry. My rough draft above shows the basic idea. The VCO is a high frequency voltage controlled rectangle wave generator with a fixed 0.5 duty time. The VCO frequency is also tunable by the external potentiometer. The voltage applied to the VCO is controlled by a voltage divider and the output of a xor gate made up of nand schmitt trigger gates. This gives it good noise immunity and some added delay which is needed in this circuit! The FM input is where music can be applied to push the coil in and out of resonance. The rectangle wave oscillator will basically be a 555 timer with a low duty cycle runnning around 1-10Hz. The frequency will be variable by adjusting the external break rate potentiometer. The interrupter circuit which is made up of the low frequency rectangle wave oscillator disables and enables the VCO output. When enabled it forces the coil to run at resonance and turns it on and off. The FM input will still beable to modulate the on time when the interrupter is enabled. The VCO's output is buffered and two complementary drive signals are produced to supply the gate driver board.

Added these fancy knobs to the external tuning potentiometer's. They are isolated from the grounded chasis to prevent coupled energy from the coil on your body from discharging to ground through your fingers which result's in nasty RF burns. Touching any grounded surfaces while the coil is running gives you RF burns so most control knobs and switch's need to be insulated from the user but chasis grounded and shielded at the same time.

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