filter - Looking for a simple way to inject a signal on 60Hz Mains line

Okay, so I'd like to be able to inject a really simple signal on top of the 60Hz AC Mains. It doesn't have to contain any data per se, just a simple signal to trigger a receiver on the same subcircuit.

I'm imagining the simplest way to do this is to create a high frequency pulse on the line that the receiver could detect with a simple bandpass filter. Essentially I would like to be able to trigger a relay remotely by sending this pulse.

I think I could make the receiver side, I'm just not sure about how to actually inject the signal.

Any advice would be much appreciated!

Answer

Microchip has a great app note on using a PIC to send and receive X10 over power lines. It is here...

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

Since you only want to send a single bit, you could just steal some of the ideas and simplify.

Here is their block diagram for injecting a signal onto the mains...

You could use a PIC or an AVR (like and arduino) to generate the carrier as shown, or if you want to keep it simple you could use something like a 555 or even an RC oscillator, but keep in mind that an MCU like an ATTINY only costs like $1 today and will give you a more accurate and stable frequency base (especially if driven by an Xtal), and opens up possibilities for sending more than one bit (like sending error correction with the bit to make detection more accurate).

Here is their block diagram for a detector...

...which again uses a Microchip PIC, but that could easily be replaced with an AVR or even just a relay.

I'd really urge you to read the whole app note as there is a great explanation of how the carrier interacts with the mains, when you should send it, and even how to power your circuit from the same connection to the mains using a transformer-less supply.