Here's how to make a microcontroller based 7 letter (or less) LED sign. Each letter is individually controlled and so you can program it to display many different patterns. It uses the darling transistor array ULN2003A to switch letters on and off. The DC voltage you use will determine the maximum number of LED's in series. For example, I used a 9 volt DC adapter and since each LED drops 2 volts, I used at most 4 LED's in series (9/2 = 4 rounded). You then connect an appropriate resistor in series and extend the number of LED'S per letter by connecting additional series sets in parallel. For example, using a 9 volt supply, a letter with 9 LED's would consist of 3 series sets: 4, 4, and 1 which are then connected together in parallel. A resistor of 50 Ohms is connected in series for each of the 4 LED's to allow 20 miliAmps of current. (9 - 2*4)/0.02A=50. The single LED gets (9 - 2)/0.02 = 350 Ohm resistor in series. As long as your power source can deliver enough current, your letters can include more LED's if necessary.
You will need to design your LED board separately since the sign will be any word or name you choose.

Step 1: Bill of Materials

Components

Capacitor .1uf
Capacitor 10uF
Capacitor 1uF
PIC16F88
7805T TO220H
Resistor 4.7K
5MM LED's
Several resistors: 50, 150, 250, 350 Ohms

Hardware

Wire
Single sided copper clad board large enough for the LED sign
3" x 3" Single sided copper clad board
PIC burner
9 Volt DC adapter

Software

Jal compiler: http://www.casadeyork.com/jalv2/
Eagle software: http://www.cadsoftusa.com/
LEDSign.jal
LEDSign.hex

PCB making

Paint thinner
Hydrogen Peroxide
Meuratic acid
Laminator
Laser Printer
LEDSign.sch and LEDSign.brd

Step 2: Build Controlling PCB

There will be 2 PCB's: the controlling PCB and the LED sign PCB.
The controlling PCB houses the microcontroller, the darlington array,
and the 5 volt regulator.
Download and Print LEDSignBoard.pdf using a laser printer on glossy paper.
You can download and import LEDSign.sch and LEDSign.brd into Eagle
to further modify the schematic and board.
Transfer the image to a copper clad board using a laminator. Drill holes
for the components. Etch the board with an acid solution.
Remove toner using paint thinner and solder in the components.
Reference other instructables on how to manufacture a PCB for more details.
The board I designed provides for 7 letters and uses 7805 to provide 5 volts
for the microcontroller. It also provides for a push button to turn off and on the lights.

Step 3: Build LED PCB

To design theLED sign, I wrote large letters in Eagle as a guide to where the LED's should go.
First draw a schematic of your LED's in series and parallel for each letter with appropriate resistors and then
design the board by rearranging the LED's to coincide with each letter. The idea is for your board to have
1 pad that receives 9 volts, or whatever voltage your power supply provides. This then is routed to
the positive side of each and every letter in your LED sign The negative side of each letter is then routed
to a seperate pad. These ground pads each get connected to the controlling PCB. A letter gets lit
when ground is supplied by the transistor array as controlled by the microcontroller.

Step 4: Programming the Controlling Board

Download and burn LEDSign.hex to the PIC16F88. It will control 6 letters in different patterns.
The programs uses the push button for going to sleep (off) when pressed and is awakened (on)
when pressed again since pushing it triggers an interrupt which wakes up on change.
Download LEDSign.jal and you can easily modify the code to create your own patterns or work
with more letters. The program itself is very basic and so it should port easily to other platforms.
If you do port it, feel free to post back and share.
JAL is a free and easy to use language for PIC's.
You can download the compiler from here: http://www.casadeyork.com/jalv2/
So there you have it. I hope you see the light. Now go and build your own signs.