Author: Esther & Fester BestertesterDate: 15:38 15-03-07
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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).
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?
FBt
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Author: Esther & Fester BestertesterDate: 15:46 15-03-07
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BTW, I'm looking for a switch that has 3 pairs of terminals and 3 positions.
Each position connects a pair of terminals together. Rocker preferred.
FBt
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Author: Esther & Fester BestertesterDate: 15:48 15-03-07
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No momentary contacts.
FBt
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Author: Lord GarthDate: 16:09 15-03-07
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"Esther & Fester Bestertester" <not@me.really> wrote in message
news:0001HW.C21EEEAB0005FB58F01826C8@news.sf.sbcglobal.net...
> 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).
>
> 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?
>
> FBt
You're partially correct re SPDT excepting that if it has a center off
position,
the switch would be labeled as such. Example: Single Pole Double Throw
center off.
The poles are the armature or internal moving portion and a throw is the
non-moving contactor that receive a pole.
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Author: Lord GarthDate: 16:27 15-03-07
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"Esther & Fester Bestertester" <not@me.really> wrote in message
news:0001HW.C21EF09000066D0AF01826C8@news.sf.sbcglobal.net...
> BTW, I'm looking for a switch that has 3 pairs of terminals and 3
positions.
> Each position connects a pair of terminals together. Rocker preferred.
>
> FBt
You're going to have to be clearer here, 3 pairs of terminals means 6
terminals.
The assumption being that your signal goes into one terminal and out the
other.
You say you wish to connect pairs of terminals together so your 3 throws
would
connect terminal 1&2 then 3&4 and finally 5&6 for example.
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.
Another possibility is that you want two signals (stereo audio perhaps) to
go to
one of 3 destinations. A rotary switch would connect the poles to throw 1
or 2
or 3 for both the left and right signals. This would still be a double pole
triple
throw rotary switch but the poles would not be shorted together.
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Author: Esther & Fester BestertesterDate: 16:37 15-03-07
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> 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)?
FBt
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Author: Homer J SimpsonDate: 16:39 15-03-07
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"Esther & Fester Bestertester" <not@me.really> wrote in message
news:0001HW.C21EEEAB0005FB58F01826C8@news.sf.sbcglobal.net...
> 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).
No, ON---ON.
It's quite possible to have a SPDT switch with no center position - some
microswitches and other sna switches are like that.
You are describing SPDT center off.
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Author: Lord GarthDate: 16:39 15-03-07
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"Esther & Fester Bestertester" <not@me.really> wrote in message
news:0001HW.C21EFC8E00093CAAF04886C8@news.sf.sbcglobal.net...
> > 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)?
>
> FBt
>
The throw has only to do with the number of positions where the pole can
complete a circuit. The off positions are not counted.
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Author: Esther & Fester BestertesterDate: 16:40 15-03-07
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> 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.
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Author: Lord GarthDate: 16:41 15-03-07
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"Esther & Fester Bestertester" <not@me.really> wrote in message
news:0001HW.C21EFD5600096B8EF04886C8@news.sf.sbcglobal.net...
> > 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.
That would be a rotary switch turned on its side!
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Author: Esther & Fester BestertesterDate: 16:56 15-03-07
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> You are describing SPDT center off.
If I want:
on - on - on
double-pole with 3 stops, what switch am I describing now?
2P3T?
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Author: Lord GarthDate: 16:58 15-03-07
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"Esther & Fester Bestertester" <not@me.really> wrote in message
news:0001HW.C21F0100000A4753F04886C8@news.sf.sbcglobal.net...
> > You are describing SPDT center off.
>
> If I want:
> on - on - on
>
> double-pole with 3 stops, what switch am I describing now?
>
> 2P3T?
Correct...this is most easily done with a rotary switch. Each pole
is a separate wafer attached axially to the shaft.
What is it you are trying to design? Maybe we can suggest some
all electronic ways to switch the signals.
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Author: EeyoreDate: 17:58 15-03-07
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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.
They're fabulously rare. Old style telephone swiches used to be able to do that.
Check out http://www.switchcraft.com/
Graham
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Author: Esther & Fester BestertesterDate: 19:47 15-03-07
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> What is it you are trying to design? Maybe we can suggest some
> all electronic ways to switch the signals.
Small DC motor speed control. Switching resistors or diodes or...? to provide
several speed choices.
12v motor pulls 2-4 amps.
Suggestions?
Thanks,
FBt
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Author: Lord GarthDate: 20:15 15-03-07
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"Esther & Fester Bestertester" <not@me.really> wrote in message
news:0001HW.C21F291D0013AE32F01826C8@news.sf.sbcglobal.net...
> > What is it you are trying to design? Maybe we can suggest some
> > all electronic ways to switch the signals.
>
> Small DC motor speed control. Switching resistors or diodes or...? to
provide
> several speed choices.
>
> 12v motor pulls 2-4 amps.
>
> Suggestions?
>
> Thanks,
> FBt
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
I'll drop copy of a modulator that ran in Electronics Design onto
alt.binaries.schematics.electronic
it's a Word doc...
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Author: Homer J SimpsonDate: 20:55 15-03-07
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Author: Homer J SimpsonDate: 20:55 15-03-07
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Author: Phil AllisonDate: 20:59 15-03-07
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"Esther & Fester Bestertester"
>
> 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).
** Nope.
SPDT = single pole, change over
3 pos switches are specified as such.
........ Phil
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Author: ehsjrDate: 23:46 15-03-07
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Esther & Fester Bestertester wrote:
>>What is it you are trying to design? Maybe we can suggest some
>>all electronic ways to switch the signals.
>
>
> Small DC motor speed control. Switching resistors or diodes or...? to provide
> several speed choices.
>
> 12v motor pulls 2-4 amps.
>
> Suggestions?
>
> Thanks,
> FBt
>
One SPDT center off switch. Conceptually:
V+ ---+---[R1]---+---[R2]---+----+
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| o | |
+--------o-> | [Motor]
o----------+ |
|
Gnd -----------------------------+
Full speed with switch down, slow speed with switch
off, medium speed with switch up.
Realisticly, using resistors has problems. Reduces
torque, and they need to dissipate a *lot* of heat
at 4 amps (I^2R). Instead, use PWM - and then you
can use a pot and get the widest possible range of
speed available, avoid the heat problem, and have
better torque.
If you absolutely cannot use a pot, then you can
still get 3 speeds using the scheme above with
PWM where the resistors select the pulse width.
They won't get hot that way and can be much smaller
wattage.
Ed
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Author: Esther & Fester BestertesterDate: 04:20 16-03-07
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> 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?
Thanks again.
FBt
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