Working progressively: Part I (LED matrix)

Posted Tue, Jan 25, 2005 at 09:12 PM

I don't feel that this entry can adequately document the full fifteen hours I spent on this thing but here goes...

(I'm going to try and be as brief as possible so if there's any questions, just comment.)

1) Prep work

So an LED matrix works by stringing together negative leads of a LED into columns and the postive leads into rows. (You can, in fact, do it the opposite way but I'll leave that up to you to figure out.)

To cut down on materials, just wire and solder are being used to make the connections between the LEDs (rather than a circuit board).

This will be an 8x8 matrix and I estimated that 3cm between each LED would be a good distance. Using my trusty Sharpie, I made 8 tick marks on a 30cm piece of wire.

2) Strip, slide, solder

Here's where the type of wire is important. (An aside: It's unbelievable how hard it is to find good wire in this town!)

Anywhere between 18-22 gauge wire works but it has to be solid (not stranded) in order for the next part to work.

I set my wire stripper to only cut through the rubber part.

At the first tick mark, I make like I'm going to strip the wire but (because I looked for the right kind of wire!) the rubber wire insulation is able to neatly slide over and expose enough bare wire for me to solder an LED onto.

IMPORTANT NOTE: You'll actually need to start with a larger area of exposed wire in the beginning because it will get progressively smaller as you move on...

Take an LED and bend the negative lead close to the base. This will help it "hook" onto the wire and give more surface area for the connection and solder.

Solder negative lead onto the wire. Having one of those "helping hands" soldering clamps helps a lot.

At the next tick mark, do the same thing again. Make sure to slide the newly loosed piece of rubber insulation snug up against the freshly soldered LED joint you just finished in order to keep bare wires (and potential short circuits) to a minimum.

And then do it again.

And again. You've got another 7 pieces of wire to go!

When you're done with the negative leads, it's time to move onto the postive leads. It's the same technique except this time it's more like weaving.

IMPORTANT NOTE: Since you're working very close to the soldered joints of the negative leads, make absolutely, positively sure that no bare wires cross each other. And that your LED leads don't cross either. Having a desoldering pump on hand also helped a lot.

This part might involve the use of even more alligator clips to make sure everyone stays on their side of the energy playground. (Which is another reason why that moveable rubber section is important.)

As you can see here, I've got a crazy setup with multiple alligator clips.

Here it is, almost done:

3) Get organized

And then it got late, and I didn't take any more pictures, so voila!

Magically, it found itself inside a balsa wood housing because I was sick of wires flopping around and getting tangled.

Balsa wood can be found in craft/art stores and are great for prototyping with because they are so easy to cut -- and poking holes for wire barely requires any energy at all.

Disorganized wire equals headaches later on down the road so I took the time to label my wires. They also sell these things called "jumper cables" ribbon cable (most commonly seen inside a computer CPU) but I didn't have any handy so... masking tape it was!

Next session: Breadboarding it.