26 Nov
2007
26 Nov
'07
3:39 p.m.
Hmm... Wonder if it's possible to build a relay
without a spring on the
switch. That is, you have to send current with one polarity to set the
switch to a 1 and reverse polarity to set a zero - sort of what core
memory does with rings... I suppose this could instead be done by
attaching a magnet to the switch, or using magnet as the thing inside
the switch body, or better yet maybe a relay with a ball with a set of
contacts as the switch and two magnets, one on each opposite side...
you'd energize one coil for a "1" and the other for a "0"
Absolutely, Such devices exist, and are normally magnetically-latched.
There are types with one coil (as you say, one polarity to 'set', the
other to 'reset') and ones with 2 coils which often you can either use as
spearate set and reset coils, or wire them togetner and use them as a
single polarity-dependant coil.
They're often used where the power required to hold a normal relay
energised would be a problem. One classic-computer applciations that I've
come across is that the cassette control relays in the cassette
interface/printer for Sharp pocket computers (PC1500, PC1350, etc) are
of this type.
I think that polaristed telegraph relays ('Carpenter relays' over here)
were designed to be stable in each state. Sort-of on-topic too...
Incidentally, remember those little 4-pen plotters that Radio Shack used
in the CGP115, Commoodore used in the 1520, etc, etc, etc. The pen
up/down solenoid in those is magnetically-latched. A pulse of one
polarity puts the pane on to the paper, a pulse of the other polarity
lifts it off again.
-tony