Voice Over Powerline (in-house)

[le_chiffre]

Hi! I'm new here. My name is Iñaki, and I'm from Argentina. I'm an electronic engineering student.
Now I'm working in a X10 project for home automation purpose as a homehowork for a Digital and Analogue Communications class. X10 is soooo slow, and only transmits for a short time of the 50hz/60hz signal. So I thought that maybe I could add some voice over powerline function in between X10 signals.
Anyone knows anything about voice over powerline (for in-house use, like talking from bedroom to kitchen) ? What kind of modulation is recommended (analogue (AM, FM), digital? It's a hard task to do? I don't care much for fidelity, so a little noise I think is not a problem.
Thank you very much, and please excuse my english (any criticism in this aspect is also welcome)

 

[chemelec]

Just amplitude modulation on a 20Khz carrier is fine.
Capacitive coupled to the line.

 

[Nigel Goodwin]

It was quite common back in the 1970's, and wireless intercoms were freely available - however, performance was always questionable?. There was quite a big movement towards both data and voice communication via the mains wiring, but it never really came to much, and it really died away. It was normal to use a low RF carrier, with either AM or FM used, but with FM prefered.

I still have a pair of Tandy (UK Radio Shack) wireless intercoms at home.

 

[le_chiffre]

Thanks, chemelec & Goodwin.

"It was normal to use a low RF carrier, with either AM or FM used, but with FM prefered. " <------- This is for wireless or powerline?

In Argentina, the electrical line is 50 hz, 220 V. The AM/FM signal I would like to transmitt, wich voltage level do you think it should be ?

 

[audioguru]

In Google, I entered Mains Intercom in the search box. Many links talked about powerline FM intercoms and baby monitors and two links had the same link to a circuit, but the circuit's link is old and doesn't work.

 

[Nigel Goodwin]

Thanks, chemelec & Goodwin.

"It was normal to use a low RF carrier, with either AM or FM used, but with FM prefered. " <------- This is for wireless or powerline?

In Argentina, the electrical line is 50 hz, 220 V. The AM/FM signal I would like to transmitt, wich voltage level do you think it should be ?

By 'wireless' I meant over the household mains wiring, the intercoms were sold as 'wireless'.

The connections at both ends of the link are usually done via isolation capacitors feeding a tuned RF transformer, actual signal level on the mains wiring is fairly low, perhaps a volt or two at the transmitter?, or even only 10's or 100's of millivolts. It's usual to have the link between neural and earth, although live and earth, or live and neutral can work as well - but the safety factor is obviously lower.

 

[Russlk]

here in the US, earth and neutral are the same; connected at the main juction box. So the signal has to be between hot line and neutral.

 

[le_chiffre]

here in the US, earth and neutral are the same;

Yeah, I think here are the same too.


For noise consideration, do you know any way of simulating powerline noise? Probably each house has his own type of noise, but I think there must be a general model....

thank you very much again

 

[audioguru]

I mentioned Google and searching for Mains Intercom. One of the links on the 1st page tested many homes and shows typical attenuation vs carrier frequency and distance. They also have 'scope photos and explanations for many types of interference they found. That's why FM is the preferred modulation to do communication over noisy power lines. Partial circuits are shown.

 

[Nigel Goodwin]

here in the US, earth and neutral are the same; connected at the main juction box. So the signal has to be between hot line and neutral.

In the UK neutral and earth are connected at the sub-station, so it works fine neutral to earth.

 

[le_chiffre]

One of the links on the 1st page tested many homes and shows typical attenuation vs carrier frequency and distance. They also have 'scope photos and explanations for many types of interference they found.

Audioguru, I searched for this pages but I couldn't find them. If you could only post the links, I'll be very grateful (more than already am :wink: ).

Thank you, good bye, and have a happy January 15.

 

[audioguru]

I found it in Google when searching for Powerline Intercom. Its a 1M PDF file and their connection is slow:
**broken link removed**

Lets see if I can upload it to here:

 

[Nigel Goodwin]

How about this Maxim IC? **broken link removed**, it says it's suitable for 'audio over powerline', you can get a full datasheet on request.

 

[le_chiffre]

Thank you audioguru


Yeah, Nigel, I saw that IC, but it seems pretty hard to get that data sheet, and even if that IC could help me, I don't think I can get it (I need to order, wait, wait, wait, and probably will be expensive). I'm trying to make this proyect as cheap as I can.

One more question: I'm looking for an open protocol for powerline communication other than X10, faster... I don't want some weird Spread-spectrum modulation but instead something simple like X10, but more powerful.

 

[Nigel Goodwin]

One more question: I'm looking for an open protocol for powerline communication other than X10, faster... I don't want some weird Spread-spectrum modulation but instead something simple like X10, but more powerful.

What do you mean by 'more powerful'?.

 

[le_chiffre]

Powerful = better data rate

 

[Nigel Goodwin]

Powerful = better data rate

But your other requirement was 'simple, like X10' - just like telephone modems you need to greatly increase complexity to increase data rate with a limited bandwidth. You 'could' increase bandwidth by increasing the carrier frequency, but increased carrier frequency means more loss through the wiring.

How fast is X10?, and how fast are you wanting to go?.

 

[le_chiffre]

more powerful = better reliable data rate

 

[Nigel Goodwin]

more powerful = better reliable data rate

In that case I suggest you investigate those Maxim chips!.

 

[le_chiffre]

How fast is X10?, and how fast are you wanting to go?.

The question is how slow X10 is, and the answer is 20 bit/s.
I don't want any specific data rate, but if I can obtain better data rates without complicating (is that the word?) the circuit and software too much, so welcome...

When I say 'simple', I mean not too complex modulation, like spread-spectrum. I was thinking maybe there is a protocol that use, I don't know, QPSK, or something like that....


thank you again