tatjna (tatjna) wrote,

In which LEDs conspire to thwart me, because they're arseholes like that

I am still new enough to electonics to experience a thrill when, after soldering everything together and plugging it in, my project actually works. Yesterday's effort was an array of 16 ultrabright UV LEDs for the lighting effect in my latest costume. Because I'm clever (and had a link to this handy calculator thing, I ended up with a circuit that looks something like this:

Where each of the resistors is 100 ohms and the whole thing's powered by a 9v battery. Neato!

First, I dug around in my components box, to discover that I have pretty much every kind of resistor except 100 ohm ones. Luckily for me, I live not far away from the font of componenty excess Happy, who happened to have some that were close enough to go on with.

A couple of hours' soldering later, I had this:

Actually, I had all 16 soldered in. As you can see, the format isn't quite the same as the circuit diagram because I wanted all the LEDs together. Anyway, I plugged it in, and it went. Mostly. 3/4 of it went, and four LEDs in one corner.. didn't.

So I tested all my connections and they were all fine, so by a process of elimination I concluded that I had a couple of dud LEDs in the circuit. I figure that since diodes only work if power's flowing through them, if one's broken in a series, it'll stop power getting to the rest. Traps for young players, test your LEDs first. Either that or I soldered them in backwards, but I'm usually pretty careful about that. Anyway, the solution is to take the offending LEDs off and replace them. Which is easier said than done. In fact, I wrecked the board trying to take them off and realised I'd have to start again.


Especially bother since I'd just used up all my 'borrowed' resistors and couldn't actually start again till I got some more. So to make myself feel better, I decided to be sensible and test all my other LEDs so I could be sure they'd work. I got about 10 tested (one dud in that lot) when one of the pins on my multimeter broke. Now, if you know anything about multimeters, you'll know that the pins have long plastic covers on the test pins so you can hold them without getting zapped:

The place where mine broke is up inside that plastic sleeve, which, incongruously for a tool that is only really used by people who are into hobby electronics (and therefore like fixing their own electronic things when they break), is a solid piece of plastic that can't be taken apart for repair.


I know when I'm beaten. After that happened, I did some nice easy analogue painting and then chilled out with some ice cream and trashy TV. Today I'll be paying Jaycar a visit for more resistors and some testing pins and a variety of other useful gubbins, and I've ordered some more LEDs just in case the duds in my remaining ones bring my useful tally below what I need.

On the upside, grist popped in with his latest invention - a little switch that involves a brass tube, a magnet, a short section of nail, and a microcontroller, that will make the LEDs switch on when I flick my wrists a la Saarebas. Nifty!

In other news, I found out on Saturday that I can base someone who is close to my own weight for quite a variety of simple adagio moves. On Sunday I found out that my muscles are *really* not used to doing that. Oww.
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