I would like to be able to switch between two circuts with one power leed.

12 volt circuit running two smal lamps.

What I would like to do is have two lamps on one power leed using a common ground. Activate circuit one by turning on the switch and not have circuit two active. Switch circuts by cyclling the power off and on.

Thanks

Alan

I'm sure I don't quite understand. However, it seems that a single-pole double-throw switch is what you want -- if you want either circuit 1 or circuit 2 on at any given time.

I grabbed this from Wikipedia. There are diagrams of single-pole single-throw and single-pole double-throw switches: Switch - Wikipedia, the free encyclopedia. See if this isn't what you want.

If you want the switches to be independent, you must split the single power lead into two and feed each one into a separate switch. The ground can still be the same common ground.

Well that is not quite what I am looking for. Think of it this way. You have two light bulbs on top of a pole. You can only have one power lead going to both bulbs, yet you want to be able to turn each one on and of separately. One switch. A flip flop circuit if there is such a thing

Let's think through this:

If there are times when you want both lights on and times when both lights would be off, and times when one would be lit but not the other then you have four states: (A-on, B-on), (A-off, B-off), (A-on, B-off), (A-off, B-on). You need a switch/circuit that can create four states. You need a switch or logic to handle these four states. Hotel rooms often have two beds and a fixture with two lamps -- one for each bed. As you push or rotate the lamp's switch, one lamp will come on, then the other, then both lamps will switch on, then both lamps will switch off. It sounds like this is the switch you want. I'm don't think I've ever used one of those and I'm not sure where to get one. I guess you could rip one off in a hotel room, but I'm sure they wouldn't appreciate that.

Look around for a double-pole, four throw switch. (DP4T or 2P4T). There's an Apem MTB24 switch that I just googled that looks like it might work. It has four positions and I assume that you can cut a trace on the bottom for the outputs that you don't want.

You could also do this with some logic circuits or a small microprocessor chip. Then you could select any of the four states at any time. But that would involve considerable expertise and possible expense.

I guess I was wrong about that MTB24 switch. You'd have to mount it to a circuit board and run traces or wires to the pins that you want to be live at the various positions.

Quote:

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Originally Posted by rwinterton

Let's think through this:

You could also do this with some logic circuits or a small microprocessor chip. Then you could select any of the four states at any time. But that would involve considerable expertise and possible expense.

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I think there lies my problem. "considerable expertise"

Ideally I would like it to change states (a then b) (ab) by just cycling the power off and on.

Hello prpldodge

If this refers to an application on a mini-railway :

The simplest solution here is to use one single wire (return current via the common), and connect the two lights via 2 diodes (A to K for lamp1 and K to A for lamp2 - i.e. reverse diodes) to the feeding wire.
At the feeding point you have a double throw switch.

Cross connect the power to S1a-S2b for +V and S1b-S2a for -V.
The wire to the top goes to S1common, and the wire to the common return to S2common.
Note : use a SEPARATE DC power supply for powering these lights.

Switch in left position : only light A is on
Switch in right position : only light B is on

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If you use a common AC supply it becomes even easier : keep wiring at the diodes and the lamps as is.
Just use a single pole switch.
Connect 1 diode to Sa (A to K) and 1 diode to Sb (K to A) and connect the diodes.
Connect the common wire to the junction of these 2 diodes.
You switch now switch either lamp 1 or lamp 2 to light.

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If you use a switch with a nil position, you can switch lights 1 or 2 on, or even both off.