The Johnson counters in the clock are made by stringing together individual flip-flops. This design uses D-type flip-flops. As I wrote before, the design of these flip-flops is copied from Simon Winder's design. He does an excellent job at explaining how they work in the following video.
I took Simon's schematic, modified it slightly to suit my needs and then made a circuit board layout in KiCad. All the 15 flip flops in the clock are exactly the same. Here is the schematic:
I ordered the cheapest 5 volts relays I could find off of Ebay. Their size is the main determining factor in the circuit layout of the flip-flops. After many revisions, this is the final board I settled on:
After lay out the circuit board, I milled the pcbs out of single sided FR-1 stock using a Roland Modela mdx-20. I want to thank Fablab Amsterdam for the many hours of machine time. I only have 160x100 circuit board blanks, so when laying out this board (and all the others in this project), I had to keep the size down and fit as many on a board as I could. Here's the result after milling six of them in one go: