A while I posted a little hint about a small project I was working on. See MINOR CHANGES. I said I would get back and report when finished. Well the hardware is finished, I am still working on the software. But I have a test program that is running right now as proof of that all the LEDs actually work and look kind of pretty. The project is simply a 50 LED matrix display. Of course this could have been easily done by purchasing a 2” square plastic LED matrix and running amok. But I had different ideas. I wanted a LED matrix to be done larger for beauty not so much for displaying text and animation. I also wanted a much larger display.
My design criteria went something like this:
5X10 LED matrix (50 total)
Widely spaced, maybe 3” apart.
Use RGB LEDs. That way I have the ability to produce any color. But that also triples the wiring and I/O.
Make the frame out of oak and the wires bare copper. No visible wiring, just LEDs floating in a copper grid of very thin wire.
The oak frame was easy in theory, but probably the most difficult part of the build. It is very difficult to tension each copper wire exactly the same, and wood flexes. So I decided to build a frame inside of a frame. Then stress each floating frame with bolts like you would piano strings.
The inside frame also had to hide all the wires, so a little routing was in order. The vertical pieces have 30 connections on each end. Ten high, three deep, one for each color. The horizontal sections only had 5 connections on each end. Oh, and none of the stressed wires could touch each other.
Electrically, I used the vertical wires attached to the horizontal sections as the ground wire. Of course they would be controlled by a micro-controller to be either ground or floating open depending on the column that needed to be activated. So they were not tied together.
The horizontal wires connected to the vertical sections were much more difficult as there were ten groups of three. To manage the wiring I did fifteen wires on one vertical section and fifteen on the other.
This was a challenge because I had to have access to the back side of the inner frame to solder and run the wires. So I build a stand to hold it together while I wired everything together and hid the wires. Then bolted the inner frame into the outer frame. After carefully tensioning the wires I then removed the stand and let the inner frame “float” inside the outer frame
All the wires were brought through holes and brass tubes into the outer frame where I made room for the micro controller, ground transistors, and multiplexing shield.
All in all I had 35 wires to land on the micro-controller and multiplexer. But first I needed to solder on each of the LEDs! Each LED has four connections. Ground/Red/Green/Blue. Each LED was placed at the intersection of vertical / horizontal wires. Consistency was the trick to making this look good. Each LED would need to be soldered on in exactly the same way so each row and each column would work and look good. For those not counting, that is 200 connections soldered on by hand.
After losing one LED and accidentally stepping on another I had to place another order with Sparkfun and wait a week to complete this project. Of course I tested each light as it was soldered on and labeled each wire. This was tedious but absolutely necessary. Lastly I mounted the micro controller and multiplexer to the inside of the frame. Next was a little programming to check the function and make sure I landed all the wires in the right place.
Anyway, here is a short video of the end product.
I will fool around with the programming when I get more time on my hands. BTW, it is powered off my USB port on my iMac. The same cable also enables me to program effects and eventually to be able to control the thing over the internet.