First of all I soldered 100 LEDs on a vero board such that they create an 8 x 10 LED matrix. After that I solded the connectors on vero board. I made the connections similiar to an 8 x 8 LED matrix. I didnt use any decoder or any other method to decrease the pins because i had an atmega2560 chip and it had enough IO pins. This was all that was to be done from the hardware end.
I used atmel studio to write the code for this project. The first thing that I did was to map out the output of each alphabet in an array. After that I simply transfered that array onto the LED Matrix. Since you can control only one LED column at a time therefore the concept of multiplexing was used here. The program was written in such a way that each led column was turns on for 1ms.