Ghetto Pixels - Building an open source BlinkM

Step 4 In which we try not to burn our fingers. again.

You can choose any one of a million different ways to put a Ghetto pixel together, and I hope that you will. (keeping it on a Breadboard, Perfboard, PCB batch, DIY PCB, conductive thread, are all great options, please show us your builds in the comments!) However, if you need some inspiration, then this is how I built mine.

I knew from the start that what I really wanted to do was to mount the LED right on top of the Chip, but there are two problems with this. First, the legs of the LED don't line up with the Legs on the chip when you sit the LED on top, and Secondly, You need to put the resistors somewhere. Adding the resitors in, sort of solves the first problem because they can be used to extend the legs of the LED to reach the pins you need to connect too on the chip.  However, I had to be a bit careful with this, as I didn't want the LED 2cm above the chip, I wanted a close as I could get to make the whole package as small as it could be.

This meant some tight soldering, directly onto the legs of the Chip and the LED *gulp* these things don't like lots of heat! and what is worse, some heavy duty clipping of wires and legs so that only the barest amount of metal was left exposed.  If I had smaller resistors to hand, I would have used them, but I didn't and had to use some 1/2 watt whoppers.

You can sort of see the build process in the photos on this step.  I started with the LED in a "helping hands" croc clip. I bent one of the resistor's legs to 90^o and soldered it as high as I could onto the LED leg, with the body of the resistor sticking out from the LED, not down. Once cooled, I clipped the leg of the LED off leaving only as much as I dared to in order to give the resistor enough mechanical strength to then be bent down so it can touch the pin of the uC.

This process was important because if the leg of the LED was left on, there is a chance that it could touch one of the pins of the uC, therefore bypassing the resistor.  Bad times. Clipping the legs off the LED was scary, but meant there was no risk of shorts.  Good times.

I found that there wasn't any really handy way of doing the resistor soldering, I had to hold the resistor in my fingers. Ouch, that sucker gets hot real quick. It's a constant reminder that no matter how hot your fingers are getting, the LED or uC is getting hotter, and you should use your Iron carefully and sparingly.

Once you have the 3 resistors soldered to the LED, and the LED pins have been shortened, put the Chip in the jaws of your vice and find the correct uC pins to solder the resistors onto. Do this carefully and more than once,  you need to be VERY sure you are soldering the right LED leg to the right uC pin.  Not taking enough care makes this into a very big and hot mess of solder and swearing.

Again, you should bend the legs of the resistors up and out (away) from the uC leg, so that they only just touch right at the base of the resistor and the top of the uC pin. YOU DO NOT WANT TO GET _ANY_ SOLDER ON THE THIN PART OF THE uC LEG (otherwise you won't get it to fit in a bread board or DIP socket again).

Get your pruning sheers out, and cut off the excess leg of the resistors so they are as trimmed as it is possible to be.   

Save one clipping of resistor leg, as you can use it to connect the common pin of the LED to the Vcc (or ground if you are rocking a common cathode) of the uC.  

stick your fingers in a cold glass of water. You are all done!

Stick the assembled Ghetto pixel back into the bread board, making sure you got it the right way round, and fire up the arduino, and sequencer, and let that lil'pixel glow.

If it doesn't work, then make sure:

• You don't have any shorts, i.e. bits of metal touching other bits of metal that they shouldn't be.
• You don't have any bad joints, i.e. bits of metal not touching bits of metal that they should be.
• It's actually sitting in the breadboard properly. Now it has some solder on it, it's pretty difficult for it to actually make contact with the tracks inside the board.

I suppose if you've tried everything, then there is a chance that you've killed either the chip or the LED with heat, but I'm not the best dude in the world with the soldering iron and while i've burnt my fingers on this project, more times than I'll admit, I've not lost a component through heat yet. You could try reprogramming the uC with the LED still attached to see if it responds (should program normally), and you could try connecting a 3V coin cell between the pins of the LED (above the resistors) to see if that still works. I'll bet both are fine.

I'll (again) assume that you've got it working, I'm an optimist like that.

We could call it a day there, but I've got a couple of other things to show you.  Let's build it out!....