Relay question

Peter Coghlan cctech at
Fri Nov 28 16:09:16 CST 2014

On 28/11/2014 at 02:23, Jim Brain wrote:
> I know this is not an electrical forum, but I thought perhaps someone 
> has seen what I am looking for.
> For an application, I am looking for a relay that is connected to 12V 
> through a switch, with the switch voltage also going to the middle of 
> a SPDT relay contacts.
>  * If I energize the latch once, for the time the button in pressed,
>    the relay flips "on" and the middle relay contact sends power to the
>    NO contact
>  * If the energize the latch a second time, for the time the button is
>    pressed, the relay flips "off" and the middle relay contact sends
>    power to the NC contact.
> The circuit works with an open relay of the kind they used to use in 
> garage doors (push button once, and door goes up, second press makes 
> it go down...)  But, we need a sealed relay to beat the weather (it's 
> for a lineman's bucket truck we own).
> Simulating this with some electronics and two relays won't work (well, 
> it would work, but it's for my father, and he really wants a 
> electrical/mechanical relay solution, like he has, but weathertight).
> I thought for sure there was such a thing as a D-type FF in relay 
> format, but all of the magnetic and mechanical latching relays I see 
> online use two separate coils to operate, which means two switches, 
> and that won't work (no more signal paths available in this application).
> I must not know what to call what I am looking for, and was hoping 
> someone had a better name for this type of thing or a suggestion of 
> where to look...
> Jim

I have come across a relay like this controlling the door of a bus.  One push
to make switch, push once to open, push once to close.  The bus schematics
called it an "impulse relay".  This is East of the Atlantic - who knows if they
they call it the same thing where you are.  The one I came across was 24V
rather that 12V too.

(There were no classic computer systems on the bus, unless you count the
radio system which allegedly tracked the bus location and radioed it back
to the controller.  It counted pulses from the speedometer/odometer
tachogenerator and did 4 bit BCD arithmatic on them using 4000 series CMOS.)

Peter Coghlan.

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