Plasma Ball/Globe Sound Mod

[Tommy Sparks]

Plasma ball sound mod. I recently bought a cheap $1.00 3-inch USB plasma ball online. the only thing fake about it was that it wasn't sound sensitive/activated/reactive. I've taken it apart (mind you I'm only 14, so I'm not particularly learned in electronics) and it seems relatively simple, about 3 resistors, something that looks like a MOSFET, about 2 capacitors, and tiny enclosed transformer connected to the mini Tesla coil thingy. I was wondering of there was some way to connect a microphone or something to make it sound reactive, or make the plasma streamers move to sound. PLEASE HELP

 

[poor mystic]

Hello Mr Sparks
a dollar for a plasma ball huh?
I guess the ones you've seen elsewhere are sound sensitive. Do you want it to flash when the big bass speakers thump?
Please tell us 1) does this plug into the mains? 2) What country are you in please?
The other thing is, can you provide a photograph of the electronics that makes it all work, please.
(smile)

 

[Tommy Sparks]

Uhh...not sure about the bass bit, but basically like the videos of these on youtube. it plugs into a USB port, its specs are 3" globe and 5V 300mA DC. It also can run on 4xAAA batteries. Heres the photos i uploaded. http://www.myupload.org/files/8ucygm08fp23xtebo3yn.jpg
http://www.myupload.org/files/ysephi0miqqrn8qzovxu.jpg
by the way whatever two black wires leading out should be to the DC
I wonder if these electret microphones can be used http://image.made-in-china.com/2f0j00BMdahkPGfobj/Microphone-Condenser-Transducer-M9745-.jpg
OR if these ceramic earphones can be used http://www.naxl.com/graphics/phonenoplug.jpg

 

[poor mystic]

Hi again TommySparks
I wonder if this circuit will do? ( I'll ask someone to have a look and tell you what is the best choice for your MOSFET)

 

[(*steve*)]

OK, poor mystic...

Firstly there are some potential problems here. The first is that the voltage available across the speakers may be insufficient to turn on the mosfet.

The second is that the time constant introduced by the 1uF capacitor may be too long to cause other than slow variations with average volume.

The mosfet would have to be a logic level device, and you may also need to consider using a small audio transformer to increase the voltage from that across the speaker terminals. It would also be a good idea to place a 10V zener between the gate and source to prevent excessively high voltages from appearing on the gate of the mosfet (unlikely, but possible).

As for a mosfet. Assume that the max current is 500mA, I would get a device capable of dissipating 2W or more continuously -- even though it's unlikely to need to do this.

This is pretty low cost, but this may be easier to fit a small heatsink to if required.

Both are overkill, but for a hack, a robust mosfet may pay off

edit: IGNORE my suggestions, they're N channel mosfets, you have drawn your circuit with a P channel mosfet

 

[Tommy Sparks]

Quote from self: "(mind you I'm only 14, so I'm not particularly learned in electronics)"
Ok....umm...sorry for wasting all your time then guys, but remember im only 14 im nowhere near as smart in electronics as you guys, and i was only going to take this up if there was a more simple solution or way, sorry but thanks a lot anyway

 

[poor mystic]

that's a shame Tommy
it isn't as bad as you'd think
we're just sussing stuff out as intercontinental committees always do. We're pretty close to a design that you can use for less than $10 and maybe less than $5.


Steve, the inputs get connected to the speakers, so there ought be sufficient voltage.
Hmm, I tried to post this 'better circuit ' earlier today, but here goes again...

 

[poor mystic]

Tommy, if you're still interested!
how loud do you listen to the music, and what wattage is your amplifier please?

 

[(*steve*)]

The first is subjective, and the second is subject to marketing fudges.

It is quite reasonable to have a 100W RMS amplifier and have the volume up about half way, producing "loud" music, yet having an average power of a couple of watts or so.

The best way would be to connect up your circuit -- don't worry about the MOSFET or the connection to the USB device -- and measure the voltage across the 1uF capacitor.

If you can't get at least 3 volts across it then you can't use the simple approach.

Note also that the current circuit connects the 0V line of the USB to one speaker connection. This may result in something as trivial (but annoying) as a ground loop, or something much more pyrotechnic if you manage to short a power supply to ground.

edit: marketing fudges refer to the use of anything BUT RMS values being used to quote amplifier power. You get the absurdity of battery powered equipment rated in excess of 400W. And by "Battery", I refer to dry cells.

 

[(*steve*)]

Ok....umm...sorry for wasting all your time then guys, but remember im only 14 im nowhere near as smart in electronics as you guys, and i was only going to take this up if there was a more simple solution or way, sorry but thanks a lot anyway

No, it's an interesting problem. We're just trying to come up with something simple that will work.

The last thing we want to do is suggest something and then have you find that it is totally non-functional (or worse).

For instance, it only recently occurred to me that coupling the USB power to the speaker like that may have unintended consequences. I considered recommending that you use an optocoupler, but that opens up another huge can of worms.

Remember that you're seeing a couple of people bounce ideas back and forth. It's not like we're discussing this in the background and coming up with a consensus opinion.

If we thought you were wasting out time, you'd know about it pretty quickly -- you'd get ignored. The fact that you're getting replies means that people are interested enough to put some effort into getting you an answer.

 

[poor mystic]

Thanks Steve, and Hi Tommy
Yes I agree completely.
But let's have a bit of a report.
My idea is that if the voltage going to your speakers is big enough, it could be made to switch a MOSFET on. A MOSFET is an electronic switch, and my idea is that when it switches on your plasma ball will start to play.
The circuit I've had in mind would take a little bit of the alternating current which drives the speaker, rectify it with a diode, and store it on a capacitor. The charge stored on the capacitor would leak away over a bit less than a second, and for the plasma ball to keep playing it would need continuing high levels of sound. For as long as a high enough voltage were present on the capacitor the MOSFET would stay "on".
The question Steve and I are having trouble with is whether the speakers really will be up loud enough for this simple circuit to work. If it turns out they're not loud enough there are solutions for that, but I think we prefer to examine the simplest solutions first.
Every electronics design is the result of some hard work.
Do you have access to a voltmeter? It would help quite a lot to know what voltage drives music into the speakers during ordinary music playback.
Mark
PS if you have any questions please ask!

 

[conductor3]

i agree ............................................................................the resistor from the input pin in my opinion can be brought down a little maybe a potentiometer may help don't take my advice seriously im only11 but know alot about circuits ............................................this may help let the sound come trough better

 

[conductor3]

and if you remove th resistor from ground and the input of the mosfet and put a button in its place you can keep it on until you push the button

 

[poor mystic]

... a pity conductor3 had not been available earlier in the piece

 

[(*steve*)]

My idea is that if the voltage going to your speakers is big enough, it could be made to switch a MOSFET on. A MOSFET is an electronic switch, and my idea is that when it switches on your plasma ball will start to play.
The circuit I've had in mind would take a little bit of the alternating current which drives the speaker, rectify it with a diode, and store it on a capacitor. The charge stored on the capacitor would leak away over a bit less than a second, and for the plasma ball to keep playing it would need continuing high levels of sound. For as long as a high enough voltage were present on the capacitor the MOSFET would stay "on".

I had thought that the idea was that the "plasma ball" flashed or pulsed in time with the music.

That was the reason I suggested a shorter time constant.

 

[(*steve*)]

and if you remove th resistor from ground and the input of the mosfet and put a button in its place you can keep it on until you push the button

You could, but you would also be creating a circuit where the gate of the mosfet was vulnerable to problems associated with exceeding Vgs. Replacing the resistor with a zener diode would function almost identically as well as providing protection for the mosfet.

This is important because the gate is essentially connected directly to an input and you don't have control of what happens inside the amplifier.

(And welcome to electronics point)