Relay computers

[Tony Duell]

> double-pole sort of "open collector". Plus, when circumstances allow it,
> you can use ONE relay coil as two inputs; the two ends of the coil
> winding are coil1 and coil2:
> 
> 
> coil1	coil2
> -v	-v	off
> -v	+v	on
> +v	-v	on
> +v	+v	off

There were/are also relays with 2 coils. The idea is that either coil 
alone will activate the contacts, but if you energise them both together 
(in opposite directions), the magnetic fields cancel out, and the 
contacts don't operate.

And of course there are magnetically-latched relays (effectively SR 
flip-flops).

-tony