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I want to hook up a push button on my photobooth following this guide.

I already have a serial cable and a port on my machine. The button I will be using is this one here.

It is an illuminated button so I would like to get power ran into it. What I am looking at using is this here.

Possibly combined with this, so that I can keep the power supply intact.

My understanding is that that piece is just wrapped around one of these.

So, what my question is, how do I know which is power and which is the ground. I want to be careful about connecting any of this to no break anything, so I thought I would check. I know that you might not be able to answer this just by looking at the parts and I don't really expect an exact answer either. I just want to know how to find out what is what when I get the parts in. If I can get one better than that I'll take that too!

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1 Answer

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Easiest thing to do is to pick up a multimeter while you're at it. Then either ohm out the connection or just measure the voltage when it's plugged in.

http://www.sparkfun.com/products/9141

http://www.sparkfun.com/products/10892

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I could have perhaps been more clear. I can get my hands on a multimeter, but I don't actually know how to use it properly, so I don't really know how to go about testing it. I figure measuring the voltage is something I understand more, but how do I check the cables. Do I attach both ends to a single wire, or one to each? When I get the 12-12.5 this thing kicks out what does that tell me? Which color on the multimeter would mean power and the other ground. I believe it's red- power black- ground, but I want to be sure. – Larmos Jun 14 '12 at 21:29
Red is power, black is ground, on the multimeter. If the power supply is plugged in and you have the red lead to one pin of the JST connector and black lead to another, and the meter reads +12V, then the pin connected to the red lead is positive. If it reads -12V, the pin connected to the black lead is positive. Alternatively, set it to measure resistance and touch one lead of the meter to the center pin of the barrel jack and the other lead to one pin of the JST connector. If it reads short, 0 ohms, then that lead is positive. This isn't always the case, but 99% of the time. – embedded.kyle Jun 14 '12 at 21:41
Awesome! Thanks for clearing that up for me. The parts are on the way and I'm excited to get this going. – Larmos Jun 15 '12 at 1:05

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