switch circuit

Idiot here looking for suggestions or links to help me find a switch for a gadget I'm working on. Switch needs to be 4-position rotary with 90 degree throw, with OFF-ON-ON-ON representing a full 360 deg. rotation.

ON 1 turns on 1 light ON 2 turns on 2 lights ON 3 turns on 3 lights

So it's like the old LOW-MED-HIGH floor lamps with three bulbs. I don't see a way to do this with a 1P4T switch, but I do with a 2P4T. I don't think I can use diodes because it's a battery operated thing and I don't want to waste any power.

I think there are other "form factors" of switches but I don't know what to look for or whether there'd be one that would be more appropriate/simpler/smaller/less expensive than using the 2P4T option.

I might need to run an amp or two through the switch, and would rather do it directly than use a relay, but I'm open to options.

TIA.

Reply to
Smitty Two
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On a sunny day (Sat, 19 Dec 2009 12:24:37 -0800) it happened Smitty Two wrote in :

Diodes, power MOSFETS

Reply to
Jan Panteltje

Do you mind using mosfets instead of diodes? In this case the power loss would be insignificant. instead of using diodes to block you will use mosfets to "block" or turn on the lights.

The idea is that the switch simple turns on a mosfet which then turns on the light. You can make it cascade so when the switch turns on one mosfet that mosfet will then turn on another. You can then build up as many lights as you want. for your case you'll only need 2 mosfets.

Pos1 turns on light one. Pos2 turns on light two and a mosfet which provides power to light one. Pos3 turns on light three and a mosfet which provides power to light two(which then turns on the other mosfet which turns on light one).

Reply to
Jon Slaughter

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AC or DC or both?

JF
Reply to
John Fields

Um... just guessing here... DC?

Jon

Reply to
Jon Kirwan

"it's a battery operated thing", Snicker ;-)

It's been a gezillion years since I last used a rotary switch, but I can recall types that sequentially tied all the contacts together. What were they called? Wafer switches? ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

I'd look the Allied Electronics catalog for something like that. But I've no idea if they carry exactly what I'm thinking of... just that they would, if it exists. I'm imagining a single pole on the axis rod with three wipers of differing radii out from the center. There would be three arcs of copper on a wafer board or bakelite, each at the appropriate radius and possessing different arc spans.

If this is a one-off, you could build it from hardware parts and some

4-gauge bare copper wire for the arcs. The circuit card within a CFL is circular and doesn't have anything on one surface to complicate things. So you might consider using that as a base. I might consider using the plasic base of a CFL (pop the bulb off) and use the circuit card (circular) as the bottom of the switch, drilling a hole in the center of that circuit board and the center of the metal base itself and place a sized bolt through there as the axis/pole of the switch. The rest would be a matter of appropriate creativity and dexterity. Many other possibilities.

Jon

Reply to
Jon Kirwan

Farnell carry a couple of multipole rotary switches. They aren't all cheap.

The Lorin CK range offers a 4-position three-pole rotary switch good for 300V ac/dc (1000V proof) that can carry 5A (non-switching)

Order code is 112-3704 and it sells for 1.11 euro a piece in small quantities.

Using one of these to control a couple of high-current MOSFETs might give you a longer-lasting solution than using it to switch the lamps directly.

-- Bill Sloman, Nijmegen

Reply to
Bill Sloman

Hmm, yeah, interesting idea. I'll try to discover whether such an animal exists. It's a proto for possible low volume production so I don't think the homemade version is going to work for me ...

Reply to
Smitty Two

Hmm, yeah, interesting idea. I'll try to discover whether such an animal exists. It's a proto for possible low volume production so I don't think the homemade version is going to work for me, though.

Reply to
Smitty Two

Mosfet, Mosfet, I remember that word from the textbooks. That was a long time ago. Let's see, FET = field effect transistor, and moss grows on trees. I like the idea, though. If I used three of them I could even use a smaller switch with a lower current rating, correct? I'll do some homework on them.

Reply to
Smitty Two

Hmm, yeah, interesting idea. I'll try to discover whether such an animal exists. It's a proto for possible low volume production so I don't think the homemade version is going to work for me, though.

Reply to
Smitty Two

Mosfet, Mosfet, I remember that word from the textbooks. That was a long time ago. Let's see, FET = field effect transistor, and moss grows on trees. I like the idea, though. If I used three of them I could even use a smaller switch with a lower current rating, correct? I'll do some homework on them.

Reply to
Smitty Two

Homemade is out, then. If you can't find something like what I mentioned above (I think I have seen similar, but not exactly what you want, on old washing machines or dryers), then I remember you said you can use a 2P4T. This link has some for $1.50 each if you buy 3 or more. $2 otherwise:

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(The "B-51652" thing.)

Jon

Reply to
Jon Kirwan

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Aaarghhh!!!
Reply to
John Fields

A mosfet is basically(or you can think of it) as an ideal switch. You apply a gate voltage(think of it as a mechanical switch with an extra terminal called a gate) and it closes the switch. Some mosfets have extremely low resistance when fully closed such as 10mohms.

If you design the circuit, you can have the switch just apply gate voltages and have the mosfets handle all the current. The switch would require extremely low current carrying capacity as the gates draw, generally, insignificant amounts of current. In this case though I believe it will require more mosfets and/or diodes.

The idea then is that the switch turns on the gates rather than the lights. Same problem(hence the reason you'll need more mosfets or diodes) but less current through the switch. It's relatively basic and shouldn't be too expensive to implement.

Reply to
Jon Slaughter

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Reply to
John Fields

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Oops...

Looks like shorting switches are only available with 30° indexing.
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Reply to
John Fields

While you were drawing that, I was drawing this:

formatting link

Am I on the right track?

Reply to
Smitty Two

No, not unless you use P-channels. The gate must be brought several volts above the source. In this case your mosfet is on the high side. If a diode is somehow turned on, note that the source voltage is then raised from ground. This means for the mosfet to stay on your gate voltage must also be raised... but this can't happen.

There are special drivers that drive the gate relative to the source for n-ch. P-ch are functionally easier to work with then on the high side because one simply applies a lower voltage to the gate to turn on the mosfet(such as grounding it). The only issues are that p-ch are more expensive(generally) and have a higher R_dson(which is why n-ch high sides are generally used).

So either come up with a new circuit that uses p-ch high side or n-ch low side.

Reply to
Jon Slaughter

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