"Relay-Based ON/OFF Flip-Flop Remembers State During Power Failure"

[PRR]

https://www.electronicdesign.com/analog/relay-based-onoff-flip-flop-remembers-state-during-power-failure

"This circuit uses electromechanical relays to retain its state indefinitely, even when power is off. It consumes no power except when triggered from one state to the other."

No semiconductors fancier than a diode. Also uses a grounded pushbutton.



The small-work PB1114-ND relay is $5 at DigiKey.com with plenty of stock.

The big-work PB2024-ND relay is $7 but out of stock.  PB2022-ND  RT424A06-ND  PB2657-ND  may be adaptable

[Beo]

So this takes a latching DPDT relay, uses one side to manage capacitor charge, and gives you an SPDT on the other side with memory. Pretty cool. But not usable as a stompbox 3pdt replacement without a second relay. Unless my understanding of this is all jacked up.

[amptramp]

There are a number of latching relays:

Potter & Brumfield LK17A and LK17D
Leach 2417
Guardian RC-100

With these devices, one pulse sets the relay to one state, the next pulse sets it to the other state and they have multiple poles or there are separate coils to set the relay to each state.  You can also get polarized relays so pulses in one direction set the relay to one state and pulses in the other direction set the relay to the other state.  This can be connected for a toggle function.  These relays hold the last state they were left in.  The named devices date back more than 60 years but may still be available.