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Registered Member #1940
Joined: Tue Jan 27 2009, 02:34PM
Location: Netherlands
Posts: 34
Hi
I build a plasma speaker some time. It works fine, but the sound level is a bit low. So I decided to change the way of audio modulation. I want to modulate it like a singing teslacoil.
I think this is the way teslacoils modulate music. The first graph is the audio input. The second graph is the output of the teslacoil.
This is schematic of my plasma speaker.
I want to put a transistor between the gate of the mosfet and the 555 chip. This chip should turn the plasma speaker on and off. The 555 chip itself is no longer audio modulated.
But how to control the transistor? A zero voltage switch? Does anyone have a schematic for this part? I don’t have the knowledge to design one myself.
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
You can turn the 555 oscillator off by pulling pin 4 (reset) low. You could for example use a comparator like the LM311 to square up the input signal, then connecting the output of the comparator to pin 4 of the 555.
Registered Member #1940
Joined: Tue Jan 27 2009, 02:34PM
Location: Netherlands
Posts: 34
Stupid question. I already found the answer on Wikipedia. It is indeed resistor R1. How high should the resistor be? I would like to use 15V input voltage. Is this possible? Should I make the voltage lower?
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
Pull up resistors usually aren't critical so you could probably use anything between 10k and 100k.
You might want to have a fairly large resistor go from the non-inverting input to ground so that the voltage doesn't drift anywhere on the other side. Maybe something around 100k.
Registered Member #1940
Joined: Tue Jan 27 2009, 02:34PM
Location: Netherlands
Posts: 34
Myke wrote ...
Pull up resistors usually aren't critical so you could probably use anything between 10k and 100k.
You might want to have a fairly large resistor go from the non-inverting input to ground so that the voltage doesn't drift anywhere on the other side. Maybe something around 100k.
If I understand you correctly, then this should be it
Registered Member #2123
Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312
Depends on what kind of source impedance pin 4 of the 555 requires for noise immunity in this application. Pin-4 is a bias to the base of an internal transistor. I'd go lower on the pullup resistor, say 2K, to prevent unwanted resets. The LM111/311 O.C. transistor can handle the current.
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How to modulated a plasma speaker to singing teslacoil
