Hey everyone! I just wanted to show you all my improved plasma speaker. Here's the video:
For those of you who are interested in it's functionality, here's a quick description of how it works, and what the circuit looks like:
Virtual Ground
The "virtual ground" section creates a third potential at half the supply voltage (in this case, 6V). R1 and R2 split the voltage in half, and that is put through an impedance converter so that voltage can't sink or rise depending on it's load. This is required because the audio amplifier requires a bipolar source to operate. The audio input is connected to this virtual ground, which means the signal coming from your Ipod or whatever is shifted up by 6 volts.
Audio Amplifier
Not much to discuss here, this is a typical configuration of the OPAMP which will amplify the signal that's inputted by the ratio between R3 and R4. In this case by a factor of 10.
AC-Coupling
Since our outputted signal is still based on the virtal ground, it will be offset by 6 volts. Therefore it is passed through an AC-coupling to filter out any DC voltages.
Squarewave generator with pulse width modulation
The TL494 is simply a squarewave generator that will change the duty cycle according to the input voltage. This means that our music will be modulated onto the squarewave signal.
Output stage with spark
Here we connect the modulated squarewave to a power MOSFET so the coil can be driven at high current. In my case a peak value of 16 Amps. For the spark gap I got myself a car ignition coil, and am able to generate 20 kV with it. A flyback transformer or something similar will do as well.
And that's it! enjoy
TheComet
