I have to be honest, I've not been very er... meticulous when it comes to keeping my LEDs in check. Let's be frank, I have a big mess of them and I've no idea which ones work or what colour they are. I'm about to start on a solar powered fairy lights project and realised I'd be spending a lot of time working out which LEDs were the ones I wanted (hence the subject of this post).
To date, I've been using a torn down dollar store hand fan for testing; I'll take a picture to show you what I mean:
It's not the easiest to use, but it outputs ~3V, has a switch and two leads (not obvious which one is positive and which one is ground though since they're both red). I ended up getting frustrated whilst holding the ends of the wires onto the LEDs and then switching over wondering if the batteries were dead, the LED was dead or if I was just crap at getting a decent connection between the leads.
Anyway, what all this blathering is getting to is that I wanted something simpler and more reliable to use. You know, something that doesn't make me want to throw it against the wall in frustration... I'd been messing with 8 pin IC sockets and perf board for other projects and realised that they are perfect for this as well. So I got together the old battery pack from the JarOFireflies prototype (which is why it has a magnet still glued on top), a small bit of perfboard, an 8 pin IC socket and 4, 330 ohm, resistors.
I soldered the resistors and socket onto the board at the same time.
I used the wires from the last resistor to solder all the connections on each side together forming two rails (positive and ground):
Then I soldered in the wires from the battery pack, connecting one to each rail, and voila!
The nice thing about this is that it's easy to check a single led without messing much with it's leads (since there's 4 holes a side, there's plenty of room) and it'll also accommodate, up to, 4 LEDs at a time:
This took about 20 mins to put together including frequent interruptions from the kids wondering what I was doing by myself in the garage.
UPDATE (2009-09-19): The resistor set-up I created is obviously crazy, I'm not sure what I was thinking (or not) at this point... The resistors should be separating pins 1 - 4 from the positive rail.