230V AC ON/OFF switching 2 light bulbs

Thread Starter


Joined Apr 1, 2017
I'm renting a flat, and cannot change wiring within a room walls, and there is only single light switch, I'd like to be able to switch between 2 light bulbs depending of needs.
So when I turn light it would light up whole room high power LED and after off/on switching it would change in to directional bulb for my working desk.
I assume it would be 2 bit binary counter made with relays, but my rusty memory failed on me. Making it work with mains AC was main issue.
Might even use single relay, considering I only need one light source at the time. It would need latch relay after off/on action.

Idea was kinda inspired by these flip of a switch bulbs


Joined Apr 17, 2019
Well... you could use a binary counter like you say, and cascade the output to a SPDT relay (one with both a normally-open and a normally-closed contact). Connect one light to the normally open, one to the normally-closed, and flip between them as the counter goes. You'd need a darlington transistor to drive the relay, driven by the counter.

You'd have to use the main power out from the switch to go to the common contact on the relay (so you have an "off" position when the switch is off), and step down the AC power to a low voltage DC as input to the counter chip.

Possible for sure - but it'll take a fair amount of circuitry. Careful with mains power for sure too - and ensure the relay and wiring are all suitably rated of course.

Thread Starter


Joined Apr 1, 2017
I have Zettler AZ850P1-5 for cheap https://www.piekarz.pl/pdf.php?id=3085
This is latching relay, so it only requires 5-14.5V DC pulse 20ms long minimum at 56-85mW to latch 875mW is max continuous dissipation.
What would be simplest circuit to give AC latching pulse at the start? capacitor dropper? simple circuit I simulated was kinda wasteful, using 6W continuously.
Using this site for simulations: http://www.falstad.com/circuit/


Joined Apr 11, 2010
It doesn’t appear that the relay you linked to can support 240VAC without modification. While the specs list 2A @ 250VAC, there is a note that when switching anything over 30VDC, special precautions are required. You are urged to contact the factory. And note those are MAXIMUM ratings.

The actual relay ratings are 1A @ 30VDC, 0.5A at 125VAV. There is no rating for 230VAC.

How are you going to provide the low voltage DC required to latch this relay? You mention an “AC starting pulse”. This can’t be for the relay...

Since the ratings are insufficient, if you were to use this and something were to happen, I wouldn’t be surprised if the landlord didn’t come after you for damages.

My solution to this problem is to plug my desk light into an unswitched plug and use its existing on/off switch.