Make a Giant LED Sign! (24x8 Matrix)

UPDATE!! Schematic is ONLINE!
UPDATE 2!! Code is ONLINE!

This project details my rather rapid build of a 24x8 matrix. 

My inspiration for this project came from Syst3mX's 24x6 matrix. A 24x6 matrix was huge, but it just was too small for me, as not much can be done in only 6 lines. My goal was to increase the line count on that display, so I could have a few extra pixels. 

Basically this is just a 24x8 matrix with a cool, interlocking foamboard grid that makes it possible to have a really big display. This display is 3 feet long, and just over a foot high! Thats half the size of a large, flatscreen TV! Plus, the whole thing is arduino controlled, so you can program it to do other cool things, besides just showing text! :)

I am just also a high school student, and i love to make stuff. So would you consider voting for this project in the current contests? Thanks!


Difficulty: This project will be pretty simple for an expert, but a beginner will struggle with it. Better for those who have had some experience with soldering/building circuits.

Cost: The entire project can be done for less than $70, much less if you already have an arduino board.

Time: 2 weekends or about 1 full season of Star Trek's work. 

Step 1: Materials

This project uses a lot of materials, so its best to have them all in one list. To build this completely, you will need

• 192 LEDs (LEDs can fail or be fried easily, so I recommend getting 200 even)
• 3 x 74HC595 shift registers
• 24 resistors (Use this to get the values you need (http://led.linear1.org/1led.wiz), you will have to know your LEDs forward voltage and current, as well as what you are supplying it with (in the case of arduino it is usually 5v sourced))
• 8 x 1k resistors
• 8 x 2N3904 transistors
• 1 x 4017 decade counter
• 1 x Arduino board or Atmega 328 chip. Make sure you have the tools to program it if you just have the chip
• Wire (lots of it!). I went through probably 50ft of wire making this. At least 50ft, if not more...
(A side note on the wire, solid core wire in a thin gauge (22-26ish), is very helpful when building this, because we will strip most of the coating of to solder it. If you can find some uncoated wire, that will help for most of the building process, and save you lots of time stripping wire)

• Tracing (sketching) paper. You can also use wax paper or parchment paper if you cannot find tracing paper
• Glue. I just used white Elmers glue and it worked great
• A foamboard panel (36 in long). I used this board from walmart, its just the right size. They had it in single-piece packages and were in the school supplies. Alternatively, you can use cardboard, or a similar type of board.
• Electrical tape (optional, but really useful)

Shameless plug- I get most of my parts from taydaelectronics.com- great store (especially for students on a budget :D), but shipping takes a while (~10 days). If you want to get it quick, I recommend Digikey or Mouser electronics. Great stores, and digikey usually gets to me in 2 days. 

Step 2: Tools

Tools you should need...


• Soldering Iron
• Wire strippers
• A laser cutter (if you have access to one). To make the full 3ft long sign I used my schools Legend 36EXT laser cutter, which has a bed 36 inches long. If you do not have a laser that big, you can scale down the parts (smaller eventual sign), or cut up the board into sections. If you do not have a laser cutter at all, you can use an X-acto knife or similar tool to cut the boards by hand. 
• Scissors 

Step 3: Cut the Foamboard

The foamboard will be cut into sections in order to create an interlocking grid for the LEDs to be placed in. 

Here are the basic drawings of what I cut them into.

This will cut the board into 34 pieces - 23 short slotted pieces, 7 long slotted pieces, and 2 each of a short and long unslotted piece. 

The first file cuts the long sections of the boards, the second cuts the short pieces, and the third piece creates a grid for the LEDs to be placed in. 

Step 4: Build the Eggcrate

So now you should have a lot of pieces to form the grid.

I started to build my grid with laying a single long piece down on a table. I then put a short piece interlocking that piece. 
After that was inserted all the way, I attached the rest of the long pieces to the one short piece. 

After this is done, you can continue to attach pieces to others until the entire grid is built.

(Note: I accidentally cut my pieces too long, adding an extra row that should not be there. I remedied this in the files I uploaded and fixed it for my final grid)

Step 5: Glue the Other Sides On

You should have an eggcrate now with open edges. Now we will use the 4 pieces that are unslotted to finish the grid off. 

To do this, I just placed some books on top of my grid (it was a bit warped, this helped flatten it out). I then places the long pieces right next to where they would eventually end up. Then I used some elmers white glue to glue them to the grid.

Use something to hold the part up to the grid while the glue sets, I used a lot of books. I also used some small nails to hold the parts together because my parts were a bit warped and uneven.

Do this for all 4 sides of the grid :)

While the glue is drying, you can move onto the next step..

Step 6: Before You Start....

Before you start, here are a few tips

-Make sure you are focused on your work, and ready to build this. It took me about 8 hours of continuous soldering to finish this. One night I worked on this until midnight, and the next morning I tried to turn it on and it would not work. It turns out, my inattentive soldering caused me about 3 extra hours of finding all the shorts and wrong connections.

-Make sure you have a clean workspace. I know it sounds pretty obvious, but I have many parts out on my workspace usually. You wouldn't want to grab the wrong part and solder it in, do you? Just remember that a clean workspace is a happy workspace.

Step 7: Solder the LEDs to the Grid

This is the most time consuming part of the entire process, soldering the LEDs to the backboard of the grid. To do this, I placed 8 leds in an extra piece of board I cut out, with the same spacing as the backboard. I then stripped a 12" piece of wire and soldered each LEDs anode (positive) lead to it. Doing this formed one column of the matrix (you need 24). Sorry about the lack of photos but I will be updating this very soon with a lot more photos and info.

After you have all the columns sorted out, it is time to solder the rows. To do this you need to bend the cathode of the LEDs (the negative lead), away from the positive lead. I bent mine at about a 45 degree angle up. I put a piece of electrical tape over all the anodes to prevent shorting, and the tape will help when you solder the cathodes.

I then stripped a 3ft piece of wire and soldered it to the cathodes, in the same method as I did the anodes. 

When you are done with this you should have 8 rows and 24 columns of LEDs.

I realize people have different methods of soldering, so do this as you will, but just remember, that all the anodes (positive) leads are in the columns, and the cathodes go to the rows. 

Step 8: Make the Circuit

I have a schematic up of all the circuitry that is going on here... I will provide an EAGLE file if anyone needs it.

There is also a PCB design attached, made by Willard2.0 (THANKS!!)

Step 9: Add Code

Here is code for the matrix that uses the serial mode on the arduino. Just open the serial monitor in the arduino software, and send text through, and it should display once on the matrix.

UPDATE: Code v1.2 - now the serial code contains every normal ASCII character! This is EVERY key on a standard US keyboard!


The serial code takes serial input from the arduino software to display text- this goes through the text once and stops...

The looping code takes a set of letters and uploads it to the arduino and loops it over and over. 

I should pause now, and thank Syst3mX, as most of this project is based off of his 24x6 matrix, even down to my schematic. Check him out, hes a great guy. My code is mostly just a modified version of his.

His code works much the same as mine will, but his is limited to 6 rows whereas mine uses the full 8

If your matrix works, go celebrate with some Ice cream...

Step 10: Cover the Board in Tracing Paper

Chances are, you didnt buy diffused LEDs, which is ok. Unfortunately though, clear LEDs have a kind of a "lens flare" effect, and are really bright in one point, making it hard to see patterns in them. To fix this, I put some tracing paper over the LEDs, effectively diffusing them. 

However, this does not diffuse them all the way, so I recommend placing another layer at the top of the grid once you attach the backboard and eggcrate together.

Step 11: Finish It!

The final step in this project is to join the eggcrate and backboard together, and maybe even make a case for the whole thing. Do this however you see fit, but just make it uniquely yours! I will be posting some pics of my completed, cased design soon.