LED Grid

This project is something that I have been working on for the past 3 years, and was finally able to finish a couple months ago. I got the inspiration for this project from a swimming pool jumbotron that had groups of 4 LEDs that combined en masse to create a giant screen. I figured that if I could control 8 channels from the parallel port, I should be able to figure out something to control more channels to make a rudimentary screen with 3-color LEDs. I started on this project with the application that was to control the grid. At this point, I had no idea how i would get the data to the screen itself or run that, but to start I needed something worth putting up. I started with some very basic designs that wiped a bar any number of pixels wide up, down, left right, diagonally etc around the screen to learn the logic. Then I combined them to make more designs with multiple colors and patterns. After the designs, i made an alphabet and created a marquise that was user-settable, and images that could move across the grid. While working on the computer, I had a process running that emulated the box by outputting HTML representing each light to a file and showing that page in a control in the UI that refreshed several times each second. Additionally, I found a control that someone had made that gave the overall sound output level of the computer (http://www.codeproject.com/KB/directx/volumemeter.aspx?df=100&forumid=328840&exp=0&select=1956575). I created an algorithm based on that to figure out what the beat of the song was, and them made an option to have the pattern change color with the beat.

After I had the software portion pretty well started I began work on the grid itself. I had read a good bit about how LCDs were made and how to control 12 LEDs x 12 LEDs x 4 leads = 576 channels, and was aware that I had to multiplex the display. Multiplexing consists of activating one row at a time and cycling through them extremely fast, taking advantage of the human eye's persistence of vision to make it appear solid. Because of this, I could take the number from 576 to 48. soldering so many LEDs, however, could have very easily gotten to be an absolute mess of wires, so I did what you can see below in the pictures, which I think is rather pretty. The RGB lines go across, and the anode lines go vertically, and they all go to a block connector that has a ribbon cable connecting it to the breadboard with the electronics, allowing it to be worked on much more easily. The LEDs are mounted in a piece of plexiglass every inch, in holes that I drilled, then hot-glued in. This was ultimately mounted into a box with a frosted piece of plexi in front of it, which gives them much better dispersion and makes it look like solid light instead of many small points.

The circuitry was the reason that the project took 3 years to complete. Since there was no way that I was going to be able to control 48 channels with a parallel port, I found a microchip that could control 24 LEDs (or channels as I used it) by feeding it a signal with a clock, then latching it in and grounding the pins that were given a high signal to complete the circuit to attached LEDs (http://www.allegromicro.com/en/Products/Part_Numbers/6276/). Stringing three of these together gave me the 48 channels that I needed, so that was a step in the right direction. Since 12 of the channels needed to be power supply rather than ground, I added an array of 12 PNP transistors that gave me the functionality I needed for that.

All this was completed my sophomore year as well, but this was the point at which I got stuck. In order to feed the LED controlling chips data to multiplex the array at all, I had to have something with the capability of sending out the required signals, and then would be able to interpret a signal from the computer with what it is supposed to display. At that time, the only thing that I and anyone I talked to could come up with to serve that purpose was a microcontroller. I had absolutely zero experience working with anything like a microcontroller, however, so after many hours trying to work that out, I shelved the project.

A few months ago, I was talking to a friend about his senior design project for Electrical Engineering, and he mentioned a chip that was a USB controller and gave 8 pins of control at high speed to a breadboard and had a C# plugin allowing it to be used with almost no effort (http://www.ftdichip.com/Products/EvaluationKits/UM232R.htm). Immediately, I recognized that this could eliminate the need for a microcontroller and allow me to finish the project; I ordered one the next day. The time from when I received the device to when it started working on the actual grid was only a few hours, which I think is pretty awesome - most of the code I wrote with very little testing and the circuits I designed with no history of circuit design or way to test them worked perfectly. It took a few tweaks on the code and device, but it is now working great. The only functionality that is not working is the volume level control; for some reason it is not registering any sound, and I did not design the control so I can't really debug it very well. I built a basic container for it with the frosted screen and all, and eventually may put it into the top of a bar. This works in a manner very similar to how the 8-switch panel sends out data; it converts Booleans to a number which is sent out to the USB/pins controller and is outputted giving the proper pins signal.

In looking to what else I can do with this project, I am considering designing a PCB that could be used with this with the LEDs on one side and the contents of the breadboard on either a brother board or the backside of the main board, so that it can have a higher LED density, as well as potentially making it extendable with connections on all four sides to connect the individual components together so that they can work together as a large screen. The code that I have is extremely easy to change for a larger grid size (it would probably only take an hour or so to make it adjustable), and that would be a really cool way to give it more real-world applications, as well as potentially mass-producible. While devices that do essentially the same thing already exist, I'm quite proud that I was able to design this from scratch with only a very basic analog circuit fundamentals class. Please let me know if you want more detail on the circuit design and series of signals to produce the desired output; I figured that would not be of interest to anyone else except someone working with the same LED controlling chips, which I can recommend as working quite well if you are doing a project with a lot of LEDs.