# Relay controll for 230Vrms main lines wireless activation and built into the wall.

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#### David_

Hello.

I have for some time had the idea to automate my apartment and enable remote activation/deactivation through some micro-controller implemented user interface and I want to find out if I can build such a switching device to be mounted in a hole in the wall. I don't know how it looks like everywhere in the world but if you live in Europe I think its a good bet that you will recognize those plastic round boxes that sits in a wall and contains mains wire connections. I don't know the there are a English term for when you make one cable into two cables or more but that is what is going on in those boxes.

Now that does not leave a huge amount of space over for a circuit board but I think I can manage that on a PCB that would contain a 230V maybe 2A relay(I have not found out how many amps that I should expect from the loads I want to control) and a IR or other wireless receiver/transmitter and finally the main subject of this thread, a tiny power supply deriving 5V or 12V from the live end of the relevant mains wire to be controlled by the relay.

I know that SMPS circuits can be made very tine as in today's phone chargers and maybe I'll just reuse one of those but I would prefer to find out what topology would be suitable for such a application(which may be implemented in the least amount of space) and learn how to do my own SMPS converter for the application.

Does any one have anything to say regarding this or regarding what is in you opinion the best choice for wireless method to use together with a micro-controller. I want to activate/deactivate as well as check status of each relay(I think there will be just one maybe two relays per PCB and box.

I will write again as soon as I have anything to show if nothing else.

Regards

#### Genovator

Its a good idea to automate your main lines. Looks cool and makes your life easy. I also have this idea for a long time to implement in my own house, but could't spare much time on developments. But I made few research to find out the best options for implementing it. I think you should have a look at TRIACS, one like these... BT136 & BT139
They also eliminates the need of SMPS. They are quite better than mechanical relays. They are soft switch, so they don't make 'tick-tock' noise like relays. Plus on resistance is low.

For wireless, IR can be used for low cost + zero noise transmission, but it would be a simplex (one way) communication. Its really hard to implement half duplex. Plus it needs line of sight.

Wireless radio modules like RF433 doesn't need line of sight, but are susceptible to noise (due to being close to main lines).
To make it a half duplex communication, you need a pair of transceivers.

David_

### David_

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##### Super Moderator
Staff member
You might want to find out how X10 works. It's a commercially marketed system which performs wireless control of appliances. It sends command signals through your existing house wiring.

It is able to do this by waiting until the moment your mains waveform crosses zero. Then it sends a brief burst of pulses into the mains wiring, which is detected by the appropriate module. The modules can control relays, dimmers, etc.

Were you thinking about a building a homemade setup that does the same thing? The usual high voltage warnings apply.

David_

### David_

Points: 2

#### David_

About the TRIAC idea, at one hand that sounds as a good idea but I can recall a video from a guy trying to control mains with triacs which worked as hoped except for the large heatsink he needed to stop the triac's from breaking after some high heat dissipation.

Have my memory corrupted this info or is some heat dissipation expected in a application turning mains voltages on/off?
That is key to this since a heatsink is out of the question in my current concept.

I do have time but I lack \$ but as soon as that situation improves I have a lot of small perhaps often unnecessary circuits to upgrade my apartment with, I want to implement my design for automated "window sun blocker things..."(Can't find English word for it roll up/down using some powerful stepper motors, a complete home-security alarm system which can be monitored and controlled through SMS or phone call followed by key-presses on the phone dial buttons. And I have a few more "upgrades" or fun stuff to do.

I have read about X10 on some forum but all I had gathered was that it was some sort of communication protocol and I had thought it to be a alternative to wifi, but sending information through pulses on the mains wire sound very funky and I can't resist such a concept, but could not those pulses be upsetting to other devices on the line?
Do you think the make it through bridge rectifiers?

In any case I will read up on it as soon as I finish this post.

Regards

##### Super Moderator
Staff member
a heatsink is out of the question in my current concept.

I made a fan speed control with a triac. No heat sink. It worked fine with a small fan.

However I broke it when I connected a window fan.

could not those pulses be upsetting to other devices on the line?

I imagine the pulses are only transmitted occasionally. Maybe your audio equipment will produce a single click.

As for their amplitude, they normally would be severely attenuated in the low impedance of house wiring. You must send the signal at a low impedance, and sufficient amplitude.

Or, there is a chance the signals are really rf, and the house wiring becomes an antenna.

Do you think the make it through bridge rectifiers?

The signal might show up in the narrow valley between diodes conducting. You must extract the signal while blocking a high voltage sine wave.

The concept has a few obstacles, which had to be overcome to make it commercially viable. It may contain a trade secret or two. If you can construct a homebrew system it will be a big accomplishment.

#### Genovator

About the TRIAC idea, at one hand that sounds as a good idea but I can recall a video from a guy trying to control mains with triacs which worked as hoped except for the large heatsink he needed to stop the triac's from breaking after some high heat dissipation.

Right. If you want to control individual points (like fan, lights, TV, etc. ) you won't be needing any heat sink. But if you want to control your house's mains 'supply', then you will need a large relay (over 10amps).

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