[Solved] Dry contacts for Wi-Fi DIY Smart Switch [86-TDQ INNOV2 2022.12.01]

Hi everyone.
This is my first post on this site. I am a beginner and I ask for your help.

I have the following Smart Switch model [86-TDQ INNOV2 2022.12.01] and I would like to understand where and how to intervene on the PCB to create a dry contact.
Thank you

Hello, the following photo is low quality and it's hard to tell where the traces go. Can you post a better quality picture?

Thanks, I'll do it right away. I hope it goes well.



Added after 1 [minutes]:

These points are joined by a track

I know that in the past I have shown how to do it precisely in Paint on the picture submitted by user, but in case of your picture, I can't see exactly how are the traces routed. It seems that contrast is insufficient or the black soldermask makes it less readable.

The general rule of thumb is that you need to:
1. find out where the relay contacts are (normally closed, normally open, and common):

2. find out how 230V (or 120V, depending on your country) goes to the power supply circuit (full bridge rectifier, etc)
3. find a way to cut out totally the mains power from the relay contacts but still route them out so they can be used as a dry relay. Depending on the board design, it may be problematic and require making an extra route with an isolated wire

Maybe posting a top side of the board could help with locating the relay, but still you'd need to track the traces correctly.
Maybe is relay there?

If that's where relay is, then you might need to cut L in such a way that it is still connected to the power supply, but does not connect to relay, but you would still need to somehow route out the second wire from relay...

Sorry
p.kaczmarek2
I didn't see your reply

Yes, but in the linked topic, I could clearly see the copper traces under the purple soldermask, and on your photo, I am not sure if I can see it.

Can you make a photo showing the board from above?

Please take all my suggestions with a grain of salt, because I may be wrong, it's hard to do that remotely, but here is how I see it:

The red path is the current path for LIVE wire that goes through the fusible resistor to the full bridge rectifier.
The yellow path is the path that current takes through relay when it's closed.
The problem is that one of relay pins is on the way....

If you want to have a dry relay here, you need to:

The very important problem is that mains is very, very dangerous!. If you really want to do it, you must make sure that there is at least of few milimeters gap between live side and dry side! You should really consider twice whether you know how to do it in safe manner. If you do it incorrectly, you may later get a short that will put mains on your dry contact.

We can summarize:
1 - Shouldn't I cut the track with "N"?
2 - Which contacts will be "Lin" and "Nin"?
3 - Which "1" and "2" are dry contacts without power?

Thank you.

Unfortunatelly there is no easy way to reroute the existing N contact. The board design was not made with a "conversion to dry relay" in mind.

If you follow my suggestions, then each terminal will keep it's role, except the "Lout" will be "Dry 2", and the extra wire you will solder to second relay pin, will be "Dry 1".

The extra wire will not be routed to any of existing terminals because I can't see a clear way to do it, but it can be routed out of the board.....

When you do this modification, make sure to keep a proper distance between live and dry terminals.

If I understand correctly, I can use the terminal block contacts in this way:



Added after 16 [minutes]:

Hi p.kaczmarek2,
If that's correct, I can close the topic and thank you warmly.

Well, you can indeed use one of two N terminals for that, but you need to do it in such a way that you can ensure a proper distance between mains lines and low voltage rail.... one milimiter of gap will not be enough.

I'll be careful.
Thanks again and see you next time
I can say it's been fixed

The moderator "p.kaczmarek2" fully answered my question.
Greetings to the whole forum