I use some of them to connect to the carry-circuits that detect the rollover to zero and clock the next digit.
I had not figured out all the wiring when I designed the flip flop boards, so I broke out the extra contacts just to be safe. I could not find cheap 5volt triple pole double throw relays, So I am using the extra contacts to drive a second double pole double throw relay, that drives the LED's. I actually need two free double throw contacts on each output to do the decoding of the digits and drive the LED display. The second pair of contacts on the output of the flip flops are not directly used. on the connection between the last and first flip flop, the Q and /Q lines are crossed/swapped. The flip flops are chained together that way. So either Set is low and reset is open or set is open and reset is low. Those are directly connected to the set and reset inputs. The output state is not just 0 or 1 on one pin, but instead it is Q: open, /Q: ground and Q: ground, /Q: open. The logic on these flip flops is slightly different from for example TTL logic chips. Hi Dan, Thanks, nice to hear that you like the project. Here's the result after milling six of them in one go: 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. I want to thank Fablab Amsterdam for the many hours of machine time. After many revisions, this is the final board I settled on:Īfter lay out the circuit board, I milled the pcbs out of single sided FR-1 stock using a Roland Modela mdx-20. Their size is the main determining factor in the circuit layout of the flip-flops. I ordered the cheapest 5 volts relays I could find off of Ebay. All the 15 flip flops in the clock are exactly the same. I took Simon's schematic, modified it slightly to suit my needs and then made a circuit board layout in KiCad. He does an excellent job at explaining how they work in the following video.
As I wrote before, the design of these flip-flops is copied from Simon Winder's design. The Johnson counters in the clock are made by stringing together individual flip-flops.
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