I feel dumb, first of all, for asking for help on this. I know there are a bunch of videos showing these things in operation.
However, I am an old man, or perhaps just a dumb man. I cannot figure out how these contraptions work from simply watching a video of a door opening and closing again.
Could some kind young soul walk an old man through (step-by-step) how to build this bloody thing? Or direct me to a video where someone actually talks and explains how to build the f**$&^ng thing?
I'm having to guess the specifics of the fishmonger in question…
This may be of use
This is nearly 4 years old, but I don't spot any mechanics I know to be broken.
With pauses & screenshots, you should be able to copy the build – but the how-it-works-part is largely absent.
Information on variations of the ABBA-type switch mentioned (not the Swedish pop group P) ) can be found @ https://minecraft.gamepedia.com/Miscellaneous_circuits#ABBA_circuit or in various videos (eg OR @~8m15 )
Hope this helps…
WARNING: I have an extemely "grindy" playstyle; YMMV — if this doesn't seem fun to you, mine what you can from it & bin the rest.