smôl Hookup Guide
PaulZC 
What is smôl?
smôl is a new board format and, as the name suggests, they're really small!
Each smôl board measures just 1.60" by 0.42" (40.6mm by 10.7mm). We made the boards just wide enough so we could squeeze USB-C and 16-way Flexible Printed Circuit (FPC) connectors on there. Some of the boards have components on both top and bottom layers which again helps keep the boards small.
smôl boards are designed to stack one on top of the other, using 16-way 0.5mm-pitch FPCs to provide the interconnect from one board to the next. Each board has an IN FPC connector on the bottom layer and an OUT FPC connector on the top layer. The boards stack in a zig-zag daisy chain; signals and power are passed from one board to the next up and down the chain through the FPCs.
We've designed a smôl Header too, which you can use to mount your smôl stack on a standard breadboard or another PCB. The Header only has an OUT connector so it needs to go at the bottom of your stack.
The order in which you connect the boards is important and we'll cover that in the next sections.