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Support Forum » Controlling a Smoke Machine with the NerdKits

August 05, 2009
by pedroh96
pedroh96's Avatar

Hey Guys!

Yesterday, I've been thinking about controlling my smoke machine with the NerdKits, and this is tottaly possible, because there is a simple ignition system to get smoke. There are two wires, and to get smoke (from the machine, :P) you just need to connect them (close the circuit). So, what I need is to close this circuit with the NerdKits.

I'm not sure but I think using a MOSFET is the best idea. Someone can tell me how can I do it?

Thanks, pH

August 05, 2009
by mrobbins
(NerdKits Staff)

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Hi pH,

This should be possible, just like how we controlled the buttons of a controller in our iPhone-controlled RC car project. But because the 2N7000 MOSFET is a n-channel device, we could really only use it to pull the signal voltage down to ground. Now, we happened to get lucky and discover that our controller did exactly that anyway. When we took it apart, we found each switch had one wire going to ground, and the other was a signal wire with a pull-up resistor. Therefore, we used a 2N7000, with the drain attached to the signal wire, the source attached to ground, and the gate going to the microcontroller. I think that you need to use a multimeter and do the same check on that system.

However, you need to be careful because you are interfacing to a wall-powered device, and by wiring up the ground of the smoke machine to the ground of the NerdKit circuit, you are relying on the fact that ground is really ground and not 120VAC (part of which is in how the device is made, and the other part is in how your electrician wired up the receptacles in your home). So if you can help it, I would avoid connecting this to your computer unless you are sure that they all have matching grounds.

If it isn't the case that the button is pulling to ground, the easiest solution is to use an optocoupler chip, like the 4N35 we used in our OBD-II car computer project. This provides lots of isolation by having essentially zero electrical connection between the NerdKit and the smoke machine. It's just an optical path (all within the small 4N35 chip). That makes it much harder for you to damage your NerdKit or your other equipment with this system, and a 4N35 is generally less than $0.50.

A relay is also an option, and like an optocoupler, provides isolation between the devices which is good for safety. But it is able to handle much higher currents which is not needed here.

Hope that helps! Show us what you come up with. Looking forward to a video of a NerdKit-controlled smoke machine!

Mike

August 05, 2009
by pedroh96
pedroh96's Avatar

Hi Mike!

Thanks for the reply. I will do some tests today and then, post the results here.

I will make a video if it works!

Oh, I found a way to control a simple laser pointer (that costs $0.50) with the NerdKits, with dimmer, strobo, and more, hahaha! I will post this too, :)

pH

August 05, 2009
by mrobbins
(NerdKits Staff)

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Hi pH,

Excellent, I love lasers!

Mike

August 05, 2009
by pedroh96
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Hey Guys!

I've been testing with a voltimeter the voltage in the switch that turns on/off the smoke.

Here is what I got:

Smoke Machine Test

How can I do this so?

Thanks, pH

August 05, 2009
by mrobbins
(NerdKits Staff)

mrobbins's Avatar

Hey pH,

I can't tell what you're measuring. Is that current? Is the button being pressed? Is the system being activated?

You've really got to figure out if this is a low-voltage signal or not. Is that a big DC transformer being used to power the smoke machine? If so, what voltage is it? These are all important clues.

Mike

August 05, 2009
by pedroh96
pedroh96's Avatar

Hey Mike,

This is current, with the circuit open (button is not being pressed). If I press the button, I don't know the voltage (but I can measure it). The system is not being activated in the photo. The Smoke Machine is being powered at 120AC.

Thanks!

August 12, 2009
by mrobbins
(NerdKits Staff)

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Hey pH,

I think your next step should be to unplug the smoke machine and try to very carefully take apart what you need to be able to "reverse engineer" a simple schematic of it, if possible. Does the operating voltage remain 120VAC throughout, or is there a transformer inside? How does the switch connect? What keeps it on for a certain amount of time? Try to do all of this without turning it on, and still be careful because their might be high voltage capacitors that hold charge (generally after a transformer and diode rectifier bridge).

Mike

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