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As presented in the picture, there are 2 Arduinos in 2 separate rooms, hooked up to the power sockets (controlling a SSR circuit for each socket).

I need a simple approach to make A1 notify A2 (in some requested circumstances that are not relevant for the problem). A simple sign of any kind sent by A1 and recognized by A2 would be enough. I cannot run additional wires, I cannot use wireless transmission, therefore the only option left is through the mains. Any ideas on how to do it? Thanks.

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    \$\begingroup\$ Why can't you use a wire, or wireless? \$\endgroup\$ – Leon Heller Mar 26 '17 at 18:34
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    \$\begingroup\$ No lines, no wireless, and simple too? And I suppose you forgot to mention that it must also be safe and reliable? I suggest you apply for Hogwarts. \$\endgroup\$ – Wouter van Ooijen Mar 26 '17 at 18:36
  • \$\begingroup\$ @LeonHeller aesthetic and practical reasons - I am actually doing this for all rooms in the house. And regarding wireless solutions, there's a lot of interference and also thick concrete walls. \$\endgroup\$ – i2r Mar 26 '17 at 18:40
  • \$\begingroup\$ @WoutervanOoijen - if there's no simple solution, I'll accept any doable one, as long as an arduino can handle it \$\endgroup\$ – i2r Mar 26 '17 at 18:49
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    \$\begingroup\$ What do you mean by 'the arduino can handle it'? You want to transmit something over the power lines, that's hard to do without extra circuitry (that will likely be more complex than an arduino). \$\endgroup\$ – Wouter van Ooijen Mar 26 '17 at 20:44
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Sending signals reliably over the mains wiring can be quite hard, especially if you are trying to impress the signal on the active wire. You can look up and read lots of information on the architecture of X10 and get lots of good ideas for coupling signals onto the mains. You could even use most of the X10 protocol to implement your schema. I have used the Firecracker (RS232 --> RF) and TM751 (RF --> AC mains) in the past successfully, though not as a transceiver.

Coupling to an Active wire can be problematic if you have multiple phases in your house (perhaps not likely for you adjacent room scenario). You have to then provide coupling between phases (even the US bi-phase is a problem here) to ensure the signal emanates to all points in your wiring.

You can avoid all the hassle by using just the Neutral and Earth wire. These wires are not phase sensitive and are both bonded to local ground near the junction box. I have used many powerline Ethernet devices (most couple to Neutral/Earth to avoid phase problems) to achieve this, and you could simply use an Ethernet Shield on your Arduino either end (you still need to provide the interface to the Earth wire of course) and you'd be good to go.

If you want to build something much cheaper, then I have used the 2.4 GHz NRF24L01 with a PA to couple signals directly onto the Earth wire. You may need to put a couple of Ferrite noise suppressors on your local ground connection wire at the earth point. (Like these). I just wrap a few turn of wire from the NRF24L01 PA antenna socket onto the earth wire at each tranciever.

You could also consider current transformer coupling onto Neutral/Earth, and that is nicely explained in a Google patent.

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What you want is called a Power Line Modem. You'd like one with a "serial TTL" interface for easy connection to your Arduino.

It is possible to build your own for less than $0.25 per node, but you need to know what you are doing when connecting to power lines or you could make a mess.

enter image description here enter image description here

http://ww1.microchip.com/downloads/en/AppNotes/00236B.pdf

Or you can buy a pre-made one.

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  • \$\begingroup\$ This is not the place to advertise goods or services. Your hidden Amazon affiliate link is a sneaky way to drive income toward yourself. This is spam, and not allowed here. \$\endgroup\$ – Dave Tweed Dec 26 '17 at 19:04

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