Superimpose a data transmission on a custom AC voltage line

Question

I hope this question is valid for this forum. I’m not looking for you to give me a working solution, my question is of the nature where I can find literature, other learning resources, which search terms I should use and/or circuits for being able to do what I describe below.

I’m designing a system where I have a host unit and more than one receiver unit. The receiver units will be powered by an AC voltage from the host. The AC voltage specifications are somewhere around:

• Vp-p = 24 VAC
• Frequency of the AC power is between 100 kHz and 200 kHz

What I would like to do is to be able add data transmission to the AC power line. It is a requirement that I won’t be able to add individual data lines. Here is a figure describing the system:

Edit
I will have full control of the AC power source. It is not a requirement that the system runs at a fixed frequency or amplitude meaning that both frequency modulation and amplitude modulation could be used for transferring data.

The data that is going to be transferred through the system does not require high speed communication. If it is possible to transmit data at UART speeds, 9600, 19200, 38400, 57600 or 115200 baud or at I2C speeds somewhere around the same transfer rate as the UART it is enough.

I have not been able to find any other sites or resources using these specific frequencies and I realise and don't expect that I will get a solution served to me. I'm grateful if I could get recommendations on literature or webpages that covers these areas.

My question:
I’m looking for resources on how to implement data transmission on a power line, in this case a custom AC power line. Books, webpages, application notes... any resource helping me with this would be helpful.

Thank you.

Answer 1

You may want to take a look at how modern Fireworks / Pyro controllers handle their power and communications. One common technique is that the master unit which supplies the power to the other units in the system uses an H-bridge to drive the pair of lines with bi-polar DC. In essence, the line pair carries a square-wave AC signal that can supply several Amps of current. Data transfer is encoded in the HI-LO transitions.

Encoding is usually Manchester but could also be a form of MFM (modified FM).

The master also leaves some dead-time between pulses so that remote units can send communications both back to the master unit as well as to other units on the buss. Obviously, this looks like a broadcast-type communications strategy where every remote unit sees the same transmitted data. That means that the remote units have some form of addressing so that they can pick off the data intended for only them.

Answer 2

I use 600 kHz for powering devices and have used superimposed data. There is nothing on the web about this and I have looked several times because I faced the same dilemma. In the end I had to design this from the floor up and sometimes that's exactly what you have to do. Unfortunately I can't give much in the way of details because it's IP.

Answer 3

I don't have much experience in this, but for sure you can start from here

I have seen LAN routers which implements the protocol over AC power lines.

Answer 4

Depending on how fast your communication has to be, and whether you can handle some disruptions in the AC power, you could simply drop some cycles according to some protocol.

Or, you could think of it as randomly reversing DC, and call one polarity a "1" and the other polarity a "0".

Or if you need close to 150kHz, you could use a "manchester encoding" scheme (google that) that runs at that speed.

Just a couple of ideas.

Answer 5

You could try G.SHDSL or something like so. It can work down to POTS bandwidth, with up to 220/230V AC lines. A ready-to-run modem costs about 100 USD/pcs. Any additional feature you may require is an appropriate splitter.