I know, I know—discussing the subject of a relay-based sequence switch in the age of omnipresent microprocessors seems to be a waste of time. After all, relays have been in use for many years. Is it possible to create something new from these already well-known relays? I tried many years ago, and I think that I succeeded.
I admit that this project is late by about 70 years, but I think its clarity of structure and operation deserves some attention. The first thing that makes it stand out is the fact that despite executing the function of a logic circuit, it does not use active electronic elements. In addition, despite the simple structure, it possesses features of much more complex digital systems.
The sequence switch, built on two-coil bi-stable relays, is partially a development of the article “Relay-Based ON/OFF Flip-Flop Remembers State During Power Failure.” In that Idea for Design article, the author, Tommy Tyler, presented a relay-based flip-flop circuit, the trigger concept of which is quite similar to my idea submitted to the Polish Patent Office over 20 years ago (Fig. 1).