Intercom project

[fisicobr]

Hello mates,
Im student of electronics and I have an idea that id like some opnions/sugestions from more experienced ppl. I dont know if theres similar project done already, but I couldnt find any info related.
So my idea is to make a intercom that uses the residential electrical wiring to conduct my signal. My energy Co supply me with a 60Hz AC power, and my 1sts divagations were to transmit my audio signal modulated by a simple AM modulator.
A simplified resume of the information flow:

Microfone -> Pre-Amplificator -> AM Modulator -> Electical wiring -> Receptor(de-modulator) -> Amplificator -> Speakers

My main question is:
*Its possible to use common residential electric wiring as line of transmission of AM signals? - Its possible to transmit signals of some KHz trough ondinary cooper conductor?

I though in some kind of digital modulation too, but it looks way more complex and expensive. I dont need HI-Fi output, I just need the output sound to be comprehensible, and it can have a very low range.
My purpose with this is didatic, so I would appreciate any theoretical/pratical input about it. Sugestions about a easier way to do this also would be very appreciated.

I must know its viability to start to work on this, hence I can have more questions .

I hope that I was clear there, English is not my native language so, sorry for my bad English.

Thank you for your attention,

Stanley

 

[JimB]

A simplified resume of the information flow:
Microfone -> Pre-Amplificator -> AM Modulator -> Electical wiring -> Receptor(de-modulator) -> Amplificator -> Speakers

OK

My main question is:
*Its possible to use common residential electric wiring as line of transmission of AM signals? - Its possible to transmit signals of some KHz through ondinary copper conductor?

Yes

The main problem is how far do you want to communicate?
Within the same building? Should be OK
To the building next door? May be OK if they are on the same phase of the electric supply.

Try AM to start with, it is nice and simple. Use a carrier frequency of 200 to 300 khz.
If you want to improve the quality, try FM, again using a low frequency carrier.

JimB

 

[Nigel Goodwin]

These sorts of schemes were popular back in the 1970's, however, it proved pretty useless, and really died off!.

 

[audioguru]

AM is interference. Light dimmers, fluorescent lights pulsing, rectifier diodes, things being turned on and off etc. Clicks and buzzing are guaranteed if you use AM.

Do telephones use the mains wiring? No, if course not. They use their own wiring like intercoms do.

 

[fisicobr]

As I said before, my purpose is didatic, im studing electronics/telecom (not College yet) and I have already some knowledge in Physics (College) so I want to make something by myself to start to get some experience. If i can make it work, then I will try to make it more refined, maybe changing it to FM and even to Digital, still with didatics purpose. Im used to theoretical knowledge and I have decent Math skills tho, but I wanna see things out of paper, and this sounded as a good thing for me to start with.
Considering all mentioned above, interference, low range, the usefullness at all is not a problem to me. Id use it at home so I dont have much sources of interference and its in no way a commercial project.

Rly thx for your answers till now, and since its not impossible, I will start to work on it. I will keep cheking here for additional information/sugestions, and updating my pregression.

Best regards.

 

[audioguru]

Don't electrocute yourself.

 

[kchriste]

These sorts of schemes were popular back in the 1970's, however, it proved pretty useless, and really died off!.

Looks like they are still being sold:
http://www.chicago-locksmith.com/Product.asp?Id=8&CatId=65&ParentId=&pn=Nutone
**broken link removed**

Usually they work with a carrier between 65kHz-75kHz. As noted earlier, use FM modulation for best noise immunity. You might want to look at the X10 system for ideas about getting the carrier on/off the AC wiring. Here is an old application note from National on how this is done:
http://www.epanorama.net/pdf_redire...edu/class/fl04/ese498/AN-146 FM Tx and Rx.pdf

 

[ecerfoglio]

Play Safe

Don't electrocute yourself.

PLAY SAFE

Use a transformer to power your circuit.

Isolate the circuit from the mains. Use a pair of capacitors in the signal path between the transmiter and the power line, another pair between the receiver and power line. The capacitors should be rated for at least 400 V (in 120V mains), 600 or 800V (in 220V mains)

Ground your circuit to the mains safety ground