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From: Andrew Smallshaw <andrews@sdf.org>
Newsgroups: comp.sys.raspberry-pi
Subject: Re: latching relays
Date: Mon, 10 Feb 2025 23:42:58 -0000 (UTC)
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On 2025-02-10, Mike Scott <usenet.16@scottsonline.org.uk.invalid> wrote:
>
> Thanks for the reply. I was considering complete units (like eg url 
> below (*)), which differ in operation. They take a pulse on a single 
> logic-level input, and flip-flop between states: my query is how to 
> reset from a random state to the power-up state.
>
> The one you reference uses either reverse polarity or a 2nd coil to flip 
> and flop.

[ https://www.amazon.co.uk/dp/B08LCTTR4Z/ ]

Those are not conventional latching relays but standard one with
an external latching circuit.  The semantics oare defiferent.
latching relays use two coildand don't need power to maintain their
state.  The page tells you all you need to know, namely the relay
is not energised when power is first applied, so conductivity is
between NCx and COMx, switching to NOx and COMx on the first pulse.

Lack of proper data sheets is one of the reasons I'm not generally
a fan of commercial building block modules like this.

-- 
Andrew Smallshaw
andrews@sdf.org