Stack Pins, holding the project together.
The boards are stacked together. This is a both blessing and a curse.
On the bright side, it keeps the boards small, it keeps critical signal paths short, and it makes expansion easy. On the downside, the more connections a project has, the more likely that something will come loose. There are so many points here that I may have created a monster. Depending on the type of pins you use, you may be able to gently solder the pins together after all the playing is done and you are ready to install the unit. I designed the board for MillMax #0038-3-17-01-30-27-02-0 , available as DigiKey ED5001-ND. The cost is a bit high, at about $25 for a six board set. I rearranged the boards to accept regular wire-wrap sockets too. In either case, we need about ½ inch between each set of boards. If you're really on a budget, you can use solid wire straight through, and you'll have the most reliable of them all. It will just be a royal pain if you ever need to split the board set for changes.
NOTE: The stackpins I mentioned will NOT work unless you solder them together. I had to do this for the build, but it was really pretty easy. They also came apart fairly easily after unsoldering them.
There is another oddity. Note the two top pins in the digital group. “Serial Data In” should connect to the “Serial Data Out” of the board below. This will require a bit of adjusting.
Whatever type of stack pins you are using, insert and solder all eight digital pins. Then turn the board over and cut off the tail of the top pin (Serial Data Out). Gently bend the tail of “Serial Data In” over a bit, so that when you stack this board it will connect to the “Serial Data Out” socket below it. This will have to be done for every channel board in the stack, including the bottom board plugging onto the output board.