A long time ago, I was given a whole load of components, including some LED matrix displays, which always looked interesting, I never got working. They require 28 bits to be shifted in, then have a column strobed - ideal job for a microcontroller: Matrix driver for HDSP-200x four character 5x7 alphanumeric displays. These are 12 pin DIL package ICs full of LEDs arranged in 4 characters of 5 columns & 7 rows each. The ones I have are the yellow HDSP-2001, but they are also available in red (HDSP-2000), high efficiency red (HDSP-2002) or green (HDSP 2003). I don't know if they are easily available anymore, but I thought, since I've got 30 or so, I'd have a go at programming them. The library is in

which is an Object Oriented way of using the display. In the constructor, you need to specify the pins used (clock/data/columns) to connect to the display. If you want to cascade more than one display IC, they have data-out, which connects to the next ones data-in, and you just shift in more bits (the library doesn't expose this externally, but it's all constants at the top, so it's fairly easy to change.

This is it combined with the network stack, I used it to display the IP address when it starts up (because I'm using DHCP, the address could be different - at least until I get around to reserving one in the router).

In this video, I used 3 ICs each displaying 4 characters, using multiple ICs doesn't require any more control lines from the mBed, since they are designed to cascade, you just send more bits before displaying the given column. Loads of wiring though, since all the control lines need copying to each display chip.