I've added a kit for making daisy chain cables to the store as the first product in our new Accessories section. It consists of a five foot length of eight conductor grey ribbon cable and six eight pin 0.1" pitch rectangular connectors compatible with the expansion connectors shipped with the six channel and sixteen channel boards.
Assembling the Cable
Attach the first connector to the cable by inserting the trimmed end of the cable into a connector. The stripe on the cable should line up with the small arrow molded into the connector, as shown. That stripe corresponds to pin 1 on the connector. It's not a big deal if it's backwards, but the rest of this HOWTO assumes that it's assembled that way. Once the cable is in the connector and lined up, squeeze it shut. I generally use a vise or a clamp like the one in the picture, but you can do it with pliers or even your teeth.
The daisy chaining works by attaching the serial output pin (pin 7) of one expansion connector to the serial input pin (pin 8) of the next, as you can see in this schematic of a daisy chain cable.
These are the two wires in the ribbon cable farthest from the stripe. Therefore, we've got to swap those pins between the lead-off connector and the next one. The easiest way to do this is to slit the insulation between the sixth and seventh wire for a short distance around where we need the next one to be. Then twist the seventh and eighth wires around so that they swap places. Slip the next connector over the cable and squeeze it into place as shown.
There's a small problem, however. The serial output pin of the second board is now connected back to the serial input of the first. While I am sure one of you folks can come up with a way to do something clever with this, it's a bad thing for most applications. Therefore, you need to clip the wire that leads from pin 8 on the first connector to pin 7 on the second.
The third connector goes on much the same way, but you don't have to twist wires seven and eight the way you did for the second one. You still need to clip the outermost wire in order to avoid having some kind of odd logic loop.
Connector four goes on like connector two and connector five goes on like connector three, and so on down the line for as many boards as you'd like to put in the chain.