12v smart relay

MassiveJim · 17 Dec 2023 at 15:51

I have a bathroom mirror which has an LED light on it which is activated by a touch switch on the front of the mirror.

I would like to have the mirror turn on with the rest of the lights in the bathroom on a motion sensor.
That in itself is very easy to do by just replacing the switch with a smart dimmer,
however the complication: I would also like to retain the use of the switch as well if possible.

currently the 240v mains power goes into a 12v transformer, then 2 wires out of that into the switch, then 2 wires from the switch to the LED strip.
The switch itself lights up blue when turned on and white when off, so I assume it has its own relay inside it.

help me please

Demon · 18 Dec 2023 at 09:58

I use Shelly products for this kind of thing, i.e. linking the lightswitch to LED lights, it's how I've done my kitchen plinth/under counter lighting.

I have a Shelly i3 that is sensing the state of the main light switch, then you just choose which ever shelly product you want for switching..

For example, you can get mini relays that can be triggered (Shelly Plus 1 Mini).. if you can fit that inside your mirror and then figure out it's internal schematic, as the touch sensor may be complex or very simple.. no reason you might not be able to use the Shelly Plus 1 Mini's Normally open/closed outputs to take over the internal LEDs from the Shelly, or the normal mirror's LED drive.. You can also get Shelly RGBW drivers (I use those for my LED strips in the kitchen)..

MassiveJim · 18 Dec 2023 at 15:49

Demon said:
I use Shelly products for this kind of thing, i.e. linking the lightswitch to LED lights, it's how I've done my kitchen plinth/under counter lighting.

I have a Shelly i3 that is sensing the state of the main light switch, then you just choose which ever shelly product you want for switching..

For example, you can get mini relays that can be triggered (Shelly Plus 1 Mini).. if you can fit that inside your mirror and then figure out it's internal schematic, as the touch sensor may be complex or very simple.. no reason you might not be able to use the Shelly Plus 1 Mini's Normally open/closed outputs to take over the internal LEDs from the Shelly, or the normal mirror's LED drive.. You can also get Shelly RGBW drivers (I use those for my LED strips in the kitchen)..

The LED strip is simple, 1 colour
the touch sensor has 2 wires in, 2 wires out, I'm not sure it can even be taken apart.

as for space, there is loads of room for putting a smart dimmer etc in there.
I have a couple of the shelly dimmer 2s, I thought they were 240v only relays though ?

the touch sensor takes its feed from the 12v transformer, not directly from the mains.

LuckyBenski · 19 Dec 2023 at 01:19

The term you might be looking for is contactor - a contactor is a relay which joins its two switchable conductors together but doesn't bridge/feed over the input supply.

I have a ZigBee contactor that can be powered from 5V USB so, I'd expect you might find one that can run off 12V.

Demon · 19 Dec 2023 at 07:49

MassiveJim said:
The LED strip is simple, 1 colour
the touch sensor has 2 wires in, 2 wires out, I'm not sure it can even be taken apart.

as for space, there is loads of room for putting a smart dimmer etc in there.
I have a couple of the shelly dimmer 2s, I thought they were 240v only relays though ?

the touch sensor takes its feed from the 12v transformer, not directly from the mains.

Without a schematic from the mirror, then it's hard to say for sure, there are many home automation products, I only mention Shelly because they are easy to intergrate together and can be configured to work locally (so no cloud) and all interact with each other, so since they do motion sensors, switch sensors, various relays and also RGBW drivers that all interconnect and can be configured to work as you want, something might be possible, but I'd say you may end up with 4 or 5 products to get it 'perfect' which may end up costing ~£100

spile · 20 Dec 2023 at 07:27

I use optocouplers when I want to use a switch between separate circuits.

MassiveJim · 21 Dec 2023 at 13:17

I think I might be wanting too much here.

there exists a scenario where the kids (or anyone really) switch on the mirror via the switch and then leave the room and the "solution" that I use would be unable then to turn off the light.

LuckyBenski · 21 Dec 2023 at 14:15

Diagram or photo might help

MassiveJim · 21 Dec 2023 at 16:13

paint skillz here we come

MassiveJim · 21 Dec 2023 at 16:22

LuckyBenski · 21 Dec 2023 at 21:39

So it seems to me you want to reproduce the "Someone touched the switch" effect any time the light is turned on, while retaining its current behaviour?

One way would be to trigger the switch - I don't know if that can be done with wires somehow. So uncertain on that solution.

Another way could be to have a contactor do the same thing the touch button unit is doing, but driven by automation. This sounds pretty workable but, it will be a case of "can't turn it off" i.e. if the automation turns the light on, you can't turn it off with the touch button. Maybe that suits you ok.

MassiveJim · 22 Dec 2023 at 13:52

LuckyBenski said:
So it seems to me you want to reproduce the "Someone touched the switch" effect any time the light is turned on, while retaining its current behaviour?

One way would be to trigger the switch - I don't know if that can be done with wires somehow. So uncertain on that solution.

Another way could be to have a contactor do the same thing the touch button unit is doing, but driven by automation. This sounds pretty workable but, it will be a case of "can't turn it off" i.e. if the automation turns the light on, you can't turn it off with the touch button. Maybe that suits you ok.

So currently when you walk in the bathroom a Samsug smart things motion sensor is used to turn on 2 seperate LED strip controllers.
And the light level and colour depends on the time of day.
It then turns them off after 5 minutes if it detects no motion.
I would like to add the mirror to this automation, but also have the option to turn it on with the switch if needed, I'm also hopeful that turning it on by the switch will always trigger it to full brightness
The mirror has a built in demister pad and when its turned on the demister is automatically on (poor design IMO) so it draws 60w when its on.

The more I think about this the more I'm thinking its not going to be possible whilst maintaining use of the built in touch switch.

LuckyBenski · 22 Dec 2023 at 17:35

You didn't mention a brightness control at all I think, that's almost certainly beyond the scope of hacking with smart stuff I think

I think what I described is doable - stand by for an awful phone diagram...

I don't think the above will solve the demister issue, and from you diagram it's directly connected to the LED power.

Note my phone doesn't have "brown" in its colour palette