It’s been eight days since my Arduino arrived and I have not been able to take my hands off it. It’s simply brilliant!
I wanted to use extra electronic components other than the Arduino alone, which I have been doing so far, so I settled to design a 8×8 LED matrix using shift registers and lot and lots of transistors.
I am using two 74HC595 Serial In Parallel Out Shift Registers for the rows and columns and software multiplexing through them to create amazing LED patters. I am using 8 PNP transistors for current sources and 8 NPN transistors for current sinking.
The matrix is constructed in a manner such that LEDs in a single row have a common anode and in a single column have a common cathode. The PNP transistors are connected to the anode side and the NPN at the cathode.
But the best part, I am only using 6 I/O pins on the Arduino to control a matrix fo 64 LEDs which when connected individually would require 128 pins. So the technique is really useful and can be extended to drive bigger displays as well.
The matrix can be used as a text display, to scroll text, display sequential patterns, the possibilities are countless.
I have a made a simple animation on the matrix which you can see in the video below. I intend to use the display as an email notifier/RSS feed display in my room, but that would require some more thought process.