Driving a neon bulb with high frequency

[Manolis]

I want to produce a 100 volt peak to peak symmetrical AC waveform to light a miniature neon bulb. It strikes at about 90 volts then settles ("clamps") at about 50 volts, according to the spec.

I want the frequency to be at least 10 kHz for easy filtering because the circuit will also be passing speech up to about 8 kHz. 20 kHz would be ideal but I don't even know whether a neon will work at such a "high" frequency. Maybe there's a sensible limit to how quickly a gas will ionise?

I suspect that I'll have to wind a ferrite transformer and drive it with a square-wave generator. (I have some ferrite rings.) I'd like to keep it simple but use discrete components (not ICs because it takes ages for orders to reach me here). Basically a "junk box" design. However, I have some NE555s somewhere.

It's after midnight here so I'm off to bed. Sensible suggestions for the design are welcomed but I won't respond for a few hours. Thanks in advance.

 

[Baluncore]

Maybe there's a sensible limit to how quickly a gas will ionise?

The neon will strike quickly. Turning it off quickly may be a problem.
What are you trying to do here? What voltage power supply do you have available?
How does the audio combine with the square wave?
An inductive flyback autotransformer will generate sufficient voltage and match an NE555 to a neon bulb.

 

[Manolis]

It's basically a psi experiment.
There's a 9v RMS transformer from which a supply can be taken.
The plasma itself or the light from it will be modulated at audio frequencies by thought control and the result is picked up by an adjacent photocell.

Q. Where can I get "an inductive flyback transformer"? CRT TV sets used to have them but are they still available? There's not a lot of physical space in the diecast box - maybe a cubic inch.
I'd prefer to wind my own if that's feasible.

Thanks for your suggestions.

 

[Baluncore]

Why do you specify a neon globe when an amber or white LED would be so much easier to control with low voltage electronics ?
Am I correct in assuming that you will use a slowly varying bio-electrical signal to control the brightness of the music modulated lamp ?
Do you have a link to a block diagram or a previous example circuit anywhere ?

 

[Manolis]

A lit neon contains a gas plasma.
(An LED will be used as a separate experiment and is easy to do.)
No music or other sound will be used, although I anticipate that the neon plasma will generate white noise.
I'm not aware of anyone else's having tried this.

 

[jim hardy]

Disposable cameras make DC to illuminate the "Flash ready" neon lamp. Most photo shops will gladly give you a bag of them.
I'd experiment with the flyback inductor from one of those and a 555 timer IC. The non-Cmos version will source or sink 200 ma.

And, with the throwaway camera you get a nice 400 volt high current capacitor for your parts box. Be careful though it's usually still charged when you rip the camera apart .

 

[Manolis]

Many thanks. I hadn't realized that cameras even used flyback circuits.

I'll have to see if I can find a shop on the island. The only one I know of sells high-end Olympus cameras but there are tourists everywhere so maybe the "kiosks" sell the disposables.

 

[jim hardy]

Many thanks. I hadn't realized that cameras even used flyback circuits.

I'll have to see if I can find a shop on the island. The only one I know of sells high-end Olympus cameras but there are tourists everywhere so maybe the "kiosks" sell the disposables.

Check the local "1 hour photo developing" shop. They should have plenty of disposables in their trash. Some have long life AA batteries, handy for your TV remote.

 

[Manolis]

I've asked my wife who last bought a disposable camera 15 years ago in England. She can't think of anywhere "local" that might sell cameras or process films. It's considered a backward Greek island but everything is "digital" here. I guess there might be somewhere in the city 160 km away. Hmm...

 

[jim hardy]

Hmmm if you see a tourist with one ask him where he got it.

 

[berkeman]

The plasma itself or the light from it will be modulated at audio frequencies by thought control and the result is picked up by an adjacent photocell.

Best of luck. Thread closed.