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Sci.Electronics.Basics -> Switch terminology?
There are 24 messages in this thread.
You are currently looking at messages 20 to 24.
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Author: Rich GriseDate: 21:51 16-03-07
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On Thu, 15 Mar 2007 12:38:03 -0700, Esther & Fester Bestertester wrote:
> 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
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Author: Rich GriseDate: 21:54 16-03-07
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On Thu, 15 Mar 2007 13:40:38 -0700, Esther & Fester Bestertester wrote:
>> If that is what you desire, a double pole triple throw rotary switch would
>> work if you short the two poles together. Rocker switches have only
>> two positions plus maybe a center off so that would not be a reasonable
>> choice.
>
> 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
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Author: Rich GriseDate: 21:56 16-03-07
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On Thu, 15 Mar 2007 13:37:18 -0700, Esther & Fester Bestertester wrote:
>> The poles are the armature or internal moving portion and a throw is the
>> non-moving contactor that receive a pole.
>
> 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
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Author: Lord GarthDate: 17:59 19-03-07
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"Esther & Fester Bestertester" <not@me.really> wrote in message
news:0001HW.C21FA149002FD866F01826C8@news.sf.sbcglobal.net...
> > You'll need a pulse width modulator to control the motor speed yet
maintain
> > good torque. There are ways to create such a modulator with an LM555
> > timer IC. You use it output to control a power FET.
> >
> > FDB603AL is such a FET and I found this one on an otherwise dead
> > motherboard. It is rated to handle 33A at 30V with a Vgs of 4.5 volts
> > and having a Rds(on) of .036 ohms
> > http://www.ortodoxism.ro/datasheets/fairchild/FDB603AL.pdf
>
> Pretty nice specs for a $1 part, especially the Rds(on). What did it power
on
> the moboard?
>
> > I'll drop copy of a modulator that ran in Electronics Design onto
> > alt.binaries.schematics.electronic
>
> 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....
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