Switch terminology?

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

No momentary contacts.

FBt

single

ie.

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.

positions.

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.

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

FBt

you

The throw has only to do with the number of positions where the pole can complete a circuit. The off positions are not counted.

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.

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.

would

That would be a rotary switch turned on its side!

If I want: on - on - on

double-pole with 3 stops, what switch am I describing now?

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.

They're fabulously rare. Old style telephone swiches used to be able to do that. Check out

Graham

Small DC motor speed control. Switching resistors or diodes or...? to provide several speed choices.

Suggestions?

Thanks, FBt

provide

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...

Yes.

What sort of load? If your budget permits, a KB controller is a good choice.

Battery DC to DC: KBBC-24M 12/24 VDC, thru 40 Amps Continuous

"Esther & Fester Bestertester"

SPDT = single pole, change over

........ Phil

One SPDT center off switch. Conceptually:

V+ ---+---[R1]---+---[R2]---+----+ | | | | | 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

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:

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

Thanks again.

FBt