Switch terminology?

[Rich Grise]

Maybe I don't understand switch terminology, but I thought SPST means single
throw (2 positions, ie. on-off) and SPDT means double-throw (3 positions, ie.
on-off-on).

Yes, but double-throw can also be on-on ; it depends if it has a stop
(detent) in the middle for the off position.

This catalog page show many switches with both terms, but mixing xST
with 2- and 3-positions. Same with xDT term.

<http://tinyurl.com/36petb>

Is my understanding incorrect? Or is this page all screwed up?

What, you worry? ;-P

This might help visualize switch terminology:
http://www.kpsec.freeuk.com/symbol.htm#switches

Good Luck!
Rich

 

[Rich Grise]

If rockers can have 3 positions:
on off on

why not:
on on on

each "on" shorting one pair of contacts.

I'm sure I've seen these before... just can't find one now.

Look for "DP3T" - double-pole, three-throw.

Good Luck!
Rich

 

[Rich Grise]

So the term "throw" has nothing to do with the positions, or "stops" that you
go through when moving the actuator (handle)?

No, "stops that you go through" is exactly what "throw" means, except for
those pesky "center-off" switches.

If the pole is the source, then the throws are the destinations.

Hope This Helps!
Rich

 

[Lord Garth]

Pretty nice specs for a $1 part, especially the Rds(on). What did it power on
the moboard?


Thanks. Without doing all the math, what R & C values would you recommend?

I found a near-identical circuit here:

http://www.discovercircuits.com/PDF-FILES/SIMPLEPWM2.pdf

Any idea what function the diodes connecting to the pwm adjustment pot
perform?

The FET is part of the power regulator circuit. You'll find these or a
compatible
part on any P4 motherboard near the CPU and near several coils. Some
procesors draw quite a large amount of power during startup. Go to a
computer
shop and pick through their junk for a "free" source of parts.

I would design the oscillator to run at say 2KHz or so. I use a simulator
program
to pick the values. Do you need a copy?

The diodes allow for a different value of R during the charging versus the
discharge
time.

Good luck....