Re: gEDA-user: spdt, spst

[Dave McGuire <mcguire@xxxxxxxxxxxxx>]

On Jan 19, 2005, at 2:31 PM, Bert Douglas wrote:
> > > > SPST ..... Single Pole, Single Throw
> > > > SPDT ..... Single Pole, Double Throw
> > >
> > > What does "pole" and "throw" mean? I know just what north and south 
> > > pole is.
> > > And also telephone pole.
> >   Picture a switch with three connections, labeled 1, 2, and 3.  At 
> > any time, electrical contact is made either between 2 and 1, or 
> > between 2 and 3, depending upon the direction of the switch handle.  
> > This would be an SPDT switch...One "pole"...one movable contact, and 
> > two "throws"...two positions in which that contact can reside.
> >   Like this:
> >   /---\                       /---\
> >   o    o    o            o    o    o
> >   1    2    3            1    2    3
> >   Get it?
> >           -Dave
>
> This is misleading, because the pole/throw nomenclature is based the 
> idea of an old fashioned knife switch, with a moving contact on a 
> pivot arm, and not on a sliding contact.
>
> The diagram shown does not generalize to three throws.

  No it doesn't, but it illustrates the paragraph above it, and it was 
the best I could do in rushed ASCII art.  Sue me. ;)

           -Dave

--
Dave McGuire              "I've watched Harley people throw up
Cape Coral, FL                      on the ceiling."    -Krissi