Polarity
(pearoast from here)

My friend Joe and I were working on cobbling together an iPod dock from plans he found on the Internet. As part of this, we had to hook a power supply up to the dock connector. Alas, the one he was going to use didn't have the polarity marked, and he didn't have a voltmeter. A dilemma.

However, he did have a drinking glass, water, and salt. So I filled the glass with salt water and stuck the power supply wires in there. The wire that gave off more bubbles would be the electrode producing hydrogen, and therefore the negative wire.

I was pretty pleased with myself, until we tried it and observed the electrodes giving off roughly equal amounts of bubbles. After an embarrassingly long time, we read the back of the power supply again and saw the text "5V AC."

We went to Radio Shack and got another power supply. And a voltmeter.
(tellum0 is spelled with an 'o', Sun 6 Dec 2009, 0:31, 7 replies)

Ha!
Impressive science fail!
( Colonel Boris "...a desperate Buzzfeed imitation...", Sun 6 Dec 2009, 10:55, closed)

thats ace that
just sat giggling after reading that, much to the annoyance of my wife watching X Factor

I'd love to explain what i'm laughing at to her, but she would just have a look at bewilderment at the AC punchline.
(Prince of Chips, Sun 6 Dec 2009, 20:02, closed)

Wow
That's gotta be pretty rare!

What the hell requires 5v AC?
( Lord Keeps meaning to procrastinate., Sun 6 Dec 2009, 20:19, closed)

Well, those are USA Vs
so that's like 10 British, right? :-D

I could be wrong on the voltage, but I do recall it being an oddball power supply. I have no idea to what it originally supplied power, and I'm pretty sure Joe doesn't either. We probably both have like $20 of copper in power supplies alone.
(tellum0 is spelled with an 'o', Mon 7 Dec 2009, 7:53, closed)

You could have bought
4 diodes instead!

And perhaps a regulator, smoothing capacitors, and some veroboard
( K2k6 has a proper job these days, Mon 7 Dec 2009, 9:51, closed)

I read that as
"4 doddies", like, AA batteries, which would be nearly right.

I'm going to call AA batteries doddies from now on.
(Richeh, Mon 7 Dec 2009, 16:47, closed)

I briefly considered the rectifier route
but I decided that step would lead only down the path of madness. Further down it than we already were, anyway.
(tellum0 is spelled with an 'o', Tue 8 Dec 2009, 4:39, closed)