The circuit is very simple – The MAX7219 connects to Arduino on pin 2, 3 and 4, and I use the sample code in the Arduino wiki (http://www.arduino.cc/playground/LEDMatrix/Max7219). The LED Driver is connected to a little 7×5 segment display I picked up at HCS (A surplus electronic store in Sunnyvale) labelled the LTP2657AA. I had to reverse engineer the pins to figure out what goes where, but manage to connect up the digits to the ground (cathodes) of the LEDs in the segment, and the segments to the positive (anodes) terminals. With one transistor (10K) to keep the voltage levels okay and following the MAXIM data sheet I managed to get it all up and running.

For future reference, here’s the pin layout of the LTP2657AA, if the notches is at the bottom, bevels at the top, and held horizontally:

rows are anodes, cols are cathodes

LEFT

1 – green row 1
2 – red row 1
3 – green col a
4 – red col a
5 – green row 2
6 – red row 2
7 – green row 3
8 – red row 3
9 – green col c
10 – red col c
11 – green col d
12 – red col d
13 – green col b
14 – red col b

RIGHT

1 – red col f
2 – green col f
3 – red col d
4 – green col d
5 – red col e
6 – green col e
7 – red row 3
8 – green row 3
9 – red row 4
10 – green row 4
11 – red col g
12 – green col g
13 – red row 5
14 – green row 5

Its quite a nice little matrix, duo color (although it only displays one at a time), and for $2 i cant complain!

so, now its all about building a sweet project.