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From: Mike Scott <usenet.16@scottsonline.org.uk.invalid>
Newsgroups: comp.sys.raspberry-pi
Subject: Re: latching relays
Date: Tue, 11 Feb 2025 15:19:57 +0000
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On 10/02/2025 23:42, Andrew Smallshaw wrote:
> 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.

OK, I get it. I'm after something that'll retain the same setting for 
extended periods, hence the desire for a latching relay to keep power 
dissipation down. Indeed, it does look as though what I've been looking 
at is a normal relay plus a flip-flop - not what I want, and I think 
you've saved me from a bad mistake.

Not wanting to mess with relay driver circuitry, I've found something 
that's definitely latching at PiHut (I hope!!). Pricey, but complete 
modules don't seem available otherwise.

Thanks to all for commenting.
> 
> Lack of proper data sheets is one of the reasons I'm not generally
> a fan of commercial building block modules like this.
> 


-- 
Mike Scott
Harlow, England