The Plasma Speaker

Step 10 How to use the plasma speaker

Here is how you can control the plasma speaker with the two potentiometers.

The 10K potentiometer is used to change the TL494's internal oscillator frequency - from 5KHz to 50KHz. If you want to play music on the arc, tune the frequency up until you don't hear it and play the music. Note: The 10K potentiometer does NOT affect the input audio (music).

I am not too sure what the 22K potentiometer's job is, but it seems to change the volume of the audio, fiddle with the 22K potentiometer until you can hear the music loudly. Note: Making the music louder will shorten the length of the arc.

Comments

[Inducktion]

Plasmana, I believe the 22k pot changes the duty cycle of the square wave. That's why it gets louder.

[spitso]

Has anyone tried endolith's schematic???? How does it work? Mofets still have heating problem? How does the arc react/sound?

[endolith]

The circuit I posted is just a modification of this one: http://scopeboy.com/tesla/flyback.html

I haven't even built it or tried it. It will be just as hot as the original, but avoids the cost of the inverter driver IC (since the TL494 already has an inverter built in).

It probably runs cooler than the Instructables circuit, though, since it has a driver FET for each power FET, which should cause them to turn on and off faster and waste less time getting hot. (But again, I haven't built any of these.)

[spitso]

heres schematic

[spitso]

That was pretty smal sorry try this linkhttp://www.instructables.com/files/orig/FVE/I3SC/FR123O01/FVEI3SCFR123O01.png

[mfkoc14]

Very impressive!!

[endolith]

Are you sure you got those right? Pin 6 controls the oscillator frequency for the TL494, but that's connected to the 22K pot in your schematic.

[Plasmana]

Yes, according to scopeboy's work... Here

[endolith]

I meant that you switched the functions of the two pots. Pin 6 controls oscillator frequency, so the 22k pot should be controlling frequency. Hmmm.... Looks like he's using a TC4429 to invert the signal, but he could do exactly the same thing by using pin 9 to drive one transistor, and pin 10 to drive the other transistor, then connecting pin 13 to pin 14 to set it for push-pull operation.

[endolith]

Here's what I meant for removing the TC4429 inverter and using the built-in inverter.

Also the two pots are labeled. The 22k pot sets the frequency in this circuit.

Full-size:
http://www.instructables.com/files/orig/FVE/I3SC/FR123O01/FVEI3SCFR123O01.png

[endolith]

(removed by author or community request)

[endolith]

Oops I made a mistake with that circuit. Pin 13 should go to Vref (pin 14), not Vcc. I'll fix it later.

[tunes]

Please post your corrected schematic.

[endolith]

I did. If Instructables let us edit comments, this would be more obvious, but people are being disagreeable about it.

[tunes]

Can the circuit be modified to use just two Mosfets? I have also seen driver circuits using a "mosfet driver chip". What are the advantages of this design over the simple 555 timer design. Is there a good way to modulate the 555 driver design for audio?

[endolith]

The MOSFET driver chips turn the FETs on and off more quickly, which minimizes the amount of time they spend wasting energy as heat, and improves efficiency. The efficiency probably doesn't matter too much, but this does allow you to use smaller heatsinks.

Here's a good explanation:
http://homepages.which.net/~paul.hills/SpeedControl/Mosfets.html

Yes, you could do this with only the two main MOSFETs, but it will be even worse for heat and efficiency, since the driver FETs in this circuit serve the same purpose as the driver ICs. Replacing these driver FETs with dedicated driver ICs would be best.

What 555 timer design are you looking at?

[tunes]

What driver IC would you suggest? Would this eliminate a heat sink for the driver FETS?

[endolith]

Well, the Scopeboy circuit uses the TC4420/TC4429. I'm not an expert on this stuff. The page I linked to above lists several others.

http://homepages.which.net/~paul.hills/SpeedControl/MosfetBody.html#4

[tunes]

endolith: Have you built the circuit without the TC4429 as you show it and how well does it work using four mosfets in terms of heating?

[endolith]

I have never built or tested this circuit. :)