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. See my notepad (http://mbed.org/users/tonymudd/notebook/led-matrix-display/) for videos of this working.