Hey folks. I'm going to prove myself not very good with electronics, as you'll soon see, so, be gentle........LOL.

Now, I can hookup an LM324 to drive an LED to an audio signal, and can filter the signal into frequency bands.

The idea is to create a circuit which can be used in sculptures which are lit from their interiors, and bounce to musical frequencies. I intend to make the sculpture concepts and the LED filter board, available to Disabled Combat Vets and Widows and provide a means of income, far above their disability and comps from govey. I hope you get the idea, although I can post images.

Now. It came to me upon the discovery of low voltage Plasma balls, they could also be implemented. (5-9 V). However, my experiments have not proved viable. They don't light up as easily as LEDs. I'm lacking voltage. I have a 12v 1500 mA power supply.

At any rate, I have an input source from my laptop headphone jack. This is connected to a small audio transformer, red to red, white to white, ground to ground, etc.

A 100k pot is connected to control gain.

Now, first, I can only get a .87 volt reading from a 1k sine wave from this circuit, so can't figure out how the LED lights up at all. But it bounces to a musical signal, just fine.

Secondly, I thought I'd solve the problem of the plasma ball lighting up by setting the ball into a voltage divider from the power source, lower than it's lowest activation, under 3V, and have the output of the LM324 put in additional volts to light up the plasma ball.

What happened, of course, was the LED stopped working, at all.

I hope someone is following all of this and can give me an idea.

Although I'm sure someone is going to tell me to put up a schematic or something.......LOL

 

You would have difficulty lighting up the plasma ball from an LM324. If they need 1500mA, then you need to consider some kind of MOSFET.

 

Thanks Tom. The ball doesn't take the entire 1500 mA, but it can soak a lot of it up. I haven't measured it, for some reason.

I finally realized that sending the opamp output to the divider, is also going to be divided, if I'm not mistaken. LOL. I cracked up when I realized that might be the issue. I was thinking a transistor might be the answer, but still not sure. Will try something like that later tonite.

I've just tried to read about what the difference is between a transistor and a mosfet, is there one? I thought transistors did work as switches...

Anyhow, thanks for your answer.

 

A MOSFET is a transistor - a type of insulated gate Field Effect Transistor. http://en.wikipedia.org/wiki/MOSFET . The confusion arises because when most people say "transistor" they mean a BJT, i.e. a Bipolar Junction Transistor. http://en.wikipedia.org/wiki/BJT . This is probably because bipolar types became widely available a long time before MOSFETS did.

Either type can be used for switching, but BJTs have the disadvantage of requiring significant drive currents to control them, and this can be problematic when switching large currents, particularly because some large power transistors have only modest current gains (ratio of controlled to controlling currents).

The MOSFET requires (almost) no drive current to the controlling gate in the steady state, although a certain amount of charge needs to flow dynamically, in the act of switching the device on or off. This makes it a popular choice for switching larger currents, but significant power can be consumed in driving the gate where high-frequency switching is required.

When turned on, a MOSFET behaves quite like a really low resistance RDS(ON), and at low currents may be able to offer lower voltage drop than you might get with a saturated transistor. Another advantage of the MOSFET is that it does not suffer from the considerable turn-off delay found with bipolar transistors following a period of saturated operation. They also are better for parallel operation, don't suffer second breakdown (ish), and lots of people like them...

But they can also be very sensitive to static damage, have none-too-predictable voltage thresholds (not quite so bad nowadays). Some older engineers also tend to think that they don't belong in linear circuits, but this is not a universally accepted view-certainly a number of linear ICs these days are stuffed with them.

To return to your question, many different devices could be used to control an amp or so, starting from a weedy op-amp. Someone who was familiar with such matters and happened to have some bipolar transistors on hand (perhaps a small one plus a power device), could likely use them. That said, a MOSFET would probably do the job with less effort.

 

http://www.vimeo.com/3906080

check this out. Tesla coil "singing"

 

I've seen that. Very cool. There's also a lot about plasma tweeters.

 

Thanks adjuster, but like I say, I TRIED to read up on them to see what the difference was, I'm not smart enough......LOL

Now. I went and bought a mosfet and here's what's going on. I have my plasma ball connected to drain, (The middle) and source to ground, and the ball is blazing away, with nothing connected to gate. Source, apparently, would be the left pin and gate, the right.

Also, it doesn't matter if source or gate is connected to ground, the plasma ball is still blazing. However, if I try to connect something to gate, even if I switch the source and gate pins, then it all shuts down and I have to pull the connector out, very fast, obviously......LOL

I've pulled everything out, but even then, I immediately get the plasma blazing and can't connect gate...

I've even watched a video and was thinking how simple this is going to be.......LOL

Any ideas?

 

You are going to have to read up on MOSFETs.

MOSFET gates are basically capacitors, once charged, you can remove the wire.. They will stay on, when you touched it with your finger, you discharged the gate, shutting it down.

 

Your MOSFET requires a certain voltage to switch it on (a data-sheet will give you its typical gate threshold voltage; a somewhat bigger value is needed to turn it on fully). You need a signal source which will reach this value reliably, say 5V for a "logic level" FET or maybe 10V for a less sensitive one.

FET gates are rather susceptible to over-voltage damage though, maybe from over 20V, e.g. from static discharge. A small Zener of say 18V connected gate-source can help prevent this. Be sure to get said Zener the right way around.

That said, these things are comparatively easy to use compared to BJTs. No worry about whether there is enough current to turn the thing on properly!

 

Ah, ok. I figured this was going to be a bust, somehow. It just sounded too good to be true.....LOL.

I tried connecting a 2222 transistor and about 1/3 of it is now in orbit around Earth. You can hear it on some ham frequencies, if it's directly above your location.....

So, what would any of you recommend? I know it couldn't be that difficult.

I know I need to take the output of whatever opamp and have that signal tell some sort of switch to turn on the plasma ball, and turn it off when there is no current.

Why is this different from a 2222 driving an LED, other than the current required is so much greater? I don't know how many amps because my meter doesn't go beyond 200 mA. Which will change tomorrow.

Anyhow, I know some of you know the answer but are going to force me to figure it out myself....

And I forgive you..........LOL

 

Well, I can see I'm going to get a lot of help here, as usual. Man, I mean that's what the site is about, not a bunch of goofballs pretending they can't read and everyone understands technical jargon, that has almost nothing to do with the problems.....LOL

What I've found is that if you take the mosfet gate and touch it to ground, it shuts off......Then, you have to connect it to your source, and it turns on again. None of which was explained in here, or on the "tutorial" site.

I just don't understand how this country functions, with so few people willing or able to help. Other than, no one seems to try anything outside of what they know how to do. Or somethin.........

I've been to Radio Shack, and they claim to know nothing about transistors or much else. Other than cell phones.

I've been to electronics repair shops and offered them double their shop rate. Nupe.

Well, I guess you can all hold your heads up with pride, you sat there and did absolutely nothing to help. For whatever that's worth.........LOL

 

I already told you, friend!

The gate ACTS AS A CAPACITOR.

You DISCHARGED it when you TOUCHED it.

You were taught, and helped. What you did with it is ALL ON YOU.

Did you type "MOSFET" in google or any other search engine?

Hopefully this helps you absorb what you have been told thus far:
http://www.youtube.com/watch?v=j47Yk7bJbxw

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Watch the WHOLE video, but 3min 44sec into you will what you saw in your own experiments, and see why.
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