[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]

Re: gEDA-user: spdt, spst



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