Connecting hardware to the Arduino
I have used 40 pin cables for this purpose, specifically, IDE cables (beware: on high speed, "80 conductor" cables, but still with 40 pin connectors, some pins are permanently connected, to indicate to to the controller that this is a high speed cable!). The connectors are cheap, the cables are free if you ask around (probably less so now). In my case, I connected two extra-large 7-segment displays, and it worked great. More pins than you rarely hurts. In my case, it was especially useful since I needed some pins at the top, and some pins at the bottom of the display; my ide cable had three connectors (motherboard &amp; two drives); I used the top row on one ide connector to the top of of my displays, and the bottom row of pins on the other connector to the bottom of the displays.