Incidentally, I made a relay flup-flop without
realising it a few months
back. I had a pair of contactors (high-power relays, basically) that
were mechnaically interlocked so they couldn't both close together
and electrically [mutually inverting-coupled].
I fairly quickly relaised it was logically
equivalent to a pair of
cross-coupled NOR gates -- the classic Eccles-Jordan circuit.
Actually, cross-coupled NAND gates - unless you count "power present"
as a logic 0, rather than 1 - because the "maintain memory" state is
I was thinkig of it as two normally-closed contacts in series -- the
control switch (which as you say is normally on, and is turned off
briefly to flip the state), and the contact of the 'other' relay.
Now, you get an output (current) iff both swtiches are in the
non-operated state (i.e. both closed). Which, denoting an unoperated
swtich as '0'. an operated switch as '1' and an output current as 1,
gives me this truth table.
In 1 In 2 Out
0 0 1
0 1 0
1 0 0
1 1 0
Which I call a NOR gate.
-tony