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first of all, sorry about to be asking that silly and newby question, I know, it is really lame.

Is there a simple device, that I can build simply, or bought, that can switch between two lights ?

I had a lamp, that has two many lamps, (7, six in a circle, and one central), all parallel, all 220v. Too much light often unused. So I thought to split in two circuits, one with the central lamp, another with the six ones.

I know I could put a commutator after the wall switch, but I do not have place, neither wires, neither looks good.

So I would like that when I turn on (on the wall), either one or six lamps goes ON, as I turn off, all goes OFF, and as I turn ON again, the opposite lamps go ON.

I can imagine, with a small circuit to remember the state, a relay, a battery, a power supply 220V to 5V, etc...

But maybe there is some short of magic relay that each time it gets 220V, it switch output ?

Again, sorry if this is a lame question ;-)

  • Are you sure power supply is 240 volt ? I If not add a simple pull chain to light. – user101687 Jun 19 '19 at 21:55
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    Why not just use a dimmer switch which will give you a continuously variable level of light and not require any new wiring or parts? – Barry Jun 19 '19 at 22:10
  • @Barry Dimmers don't always work well with fluorescent or LEDs. – manassehkatz-Moving 2 Codidact Jun 19 '19 at 22:14
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    The OP did not mention what type of bulbs he has. However I doubt they are fluorescent and dimmers for LEDs are readily available. I have several in my house. – Barry Jun 19 '19 at 22:20
  • Can you run more wires between the light-box and the switch-box, or is that not an option for you? – ThreePhaseEel Jun 19 '19 at 22:34
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There probably is a switch out there that can do it - with three states - Off, A, B. Wire A to one light, B to the other lights. But I think a far simpler solution - or at least far more common in terms of inexpensive parts is to use two switches. The first switch would function as On/Off. The second switch would function as A/B. The second switch would be (in US terminology) a 3-way switch, but instead of using it as a 3-way switch, which typically lets you use 2 separate switches to turn a single light On/Off from either location, you would use it to switch two different lights (or groups of lights). In addition, you can get two switches in one box, like this: enter image description here You wire the first 3-way as a single switch with one output ("traveler") going to the second switch and the second output not connected at all. You wire the second 3-way switch so that one output goes to one light ("A") and the other output goes to the other light ("B"). Whenever you turn the first switch on, the light status (A or B) will be the same as it was the last time you used it.

No batteries. No relays. No "smart" switches. Just a pair of ordinary switches.

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    If you are going to put in 2 switches then why not simply use one for the single bulb and the other for the group of 6? They can then both be simple on/off switches and you would have the added convenience of being able to have all 7 bulbs on at the same time. But I'm guessing you don't want to add more wires in the wall, rather a circuit in the lamp that will swap between two states on the existing wiring. – Peter Jennings Jun 20 '19 at 1:21
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    The only difference is this gives you specifically switch from A to B. But two normal switches is fine too - as long as you don't mind All On as an option. There can be situations where All On would be a real problem in terms of total power but that's not the case here. – manassehkatz-Moving 2 Codidact Jun 20 '19 at 1:51
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Your question is not lame at all. Actually it can lead to a pretty cool project.

I'm not sure whether your goal is simply to solve a lighting problem or to design something fancy you could be proud of.

If it's the former, just adding more wiring and an extra switch on the wall is probably your best bet.

If it's the latter than your idea of using "a small circuit to remember the state, a relay, a battery, a power supply 220V to 5V, etc." can lead you to the right direction.

Essentially you need some sort of state machine with at least two different states: powering the lights in the circle, or powering the central light.

One problem here is that when the wall switch goes off you loose power completely, what makes it hard for your gadget to remember the last state when power comes back. The solution could be to use a battery or supercap inside your gadget or to add a small capacitor in parallel to your wall switch so would allow you to harvest a small amount of power even when the switch is off. Another simpler idea is having some capacitance in your gadget that is good enough to remember the last state for just a few seconds. So if you turn the switch on after a long period of time, it would always go to the same state, but if after that you flip the switch off and on again, it would go to the other state. It sounds like a good compromise to me.

Another problem is that it's tricky to implement state machines with such high voltages (220V AC). Maybe there is a creative way of doing it with thyristors... The option may be to build a small 5V DC supply as you suggested and then implement your circuit with logic gates and flip flops or even using a micro controller. Then you would need relays to actually turn the 220V lights on. You could use solid-state relays or mechanical ones.

I may have provided more questions than answers... I hope I have helped somehow.

Good luck in your project!

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There are numerous bi-stable mechanical devices, including pull switches, that require no permanent power input to maintain them in either state, just a push (or pull) to swap their state. Maybe you could devise a setup whereby such a switch receives a momentary pull from a solenoid as the power is switched on, then it becomes de-energised. What you don't want, if it can be avoided, is a solenoid or relay permanently drawing power (and getting hot) all the while the lamp is on.

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