Re: gEDA-user: spdt, spst

[Bert Douglas <bertd@xxxxxxxxxxxxx>]

Dave McGuire wrote:

> On Jan 19, 2005, at 1:31 PM, Karel Kulhavy 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.