sending voice on the mains power cable

[eoinitb]

i want to design some hardware to send voice and if possible video over the mains 50 hz 220 v power rails can anyone suggest a circuit or where to start looking. cheers

[jwax]

Look at "wireless" intercoms that plug into wall outlets for audio, however video would probably have to be digitized.
What range are you looking for?

[dyarker]

Repeat of jwax's "What range are you looking for?"<p>To keep power line spikes and noise out of the audio it could be FM modulated to like 25KHz - 40KHz.<p>Video is harder. You want a clear image, but you don't want the nieghbors seeing you as a ghost on every channel either. Slow scan TV might be possible. (Yeah, I know there are systems for ethernet over power lines, but manufacturers can get special ICs and have more than one engineer.)<p>The most important thing for safety, is decoupling the signal from AC power. 220VAC, 50Hz power uses non-polarized plugs (except U.K. I think), so you must decouple from both 220V and neutral.

[eoinitb]

this is a college project so design is more important than application the actual part of getting it onto the 220v mains cables without frying myself that i was having troble with .i have never used any form of transformers before and i understand i need to use them this time so any help with that would be great transmitting audio with a carrier around 25khz would be fine the video aspect i can consider later
cheers<p>eoinf

[haklesup]

To inject your small signal (low amplitude, high frequency) onto the power line (large amplitude, low frequency) you need a series capacitor. One that would be an open (high impedance) at 50/60Hz but be low impedance at the carrier frequency (assuming FM)(AM could cause interference with other things plugged into the line). <p>The voltage rating of the cap should be at least the line voltage but 2X more makes for a nice margin. A non-polarized cap would also be appropriate for this application.<p>This in not alltogether different seperating a DC and AC signal component (decoupling)<p>I'm not sure of a value to recommend (though it won't be a large value as this will pass the 50/60hz signal). It depends on the signal you want to pass through it. Being in college, you are a lot closer to the math than I am (20yrs out of school). There is probably a range of acceptable values.<p>Look at this website http://www.geocities.com/IDO_Bartana/ to see how X10 equipment does it for a digital signal. Keep in mind that your signal will have a different carrier frequency and thus require different values for decoupling also theirs is synched to the zero crossing which is not required for yours<p>There are other ways to inject a signal. One way may use a transformer but it is unfamialiar to me so I won't go into it much but it seems a second primary winding could be used to piggy back an AC signal onto the primary power signal so long that both signals had frequencies that can saturate the transformer. The design calculations required to determine the number of turns and core properties should be worth a few points on your grade that as well as specifying the amplitude, drive current, carrier frequency and modulation method of the driver circuit.<p>Have fun,

[cato]

The big boys call that Broadband over Power Line. <p>The ARRL is trying to fight it because of all the noise it will radiate. I'm sure you will find plenty about it with a quick google search.

[jollyrgr]

What level of video are you wanting to send? In the US television video signals are 4MHz wide. I do not think that either NTSC or PAL fast scan signals will work over powerlines.<p>If you want some sort of slow scan video, this is quite easy. If you use a video signal in an audio passband you can easily use a carrier current radio transmitter to pass this same signal. Slow Scan Television or SSTV is popular among hams and can even be done with a computer soundcard.
See this link:
http://www.sstvham.com/<p>Now to the transmitter part of your question. What you want look up is "carrier current" transmitters. These were quite popular on college campuses at one time and may still exist in a few. Here is a "white paper" on the subjet in PDF format:
http://www.collegebroadcasters.org/ccte ... Theory.pdf<p>The audio portion is easy, simply inject the audio into a transmitter at one frequency, 550kHz for example, and tune an AM radio to 550kHz. The video may be a bit more complex. <p>Amateur radio operators use less bandwidth than a typical carrier current radio transmitter. And they can send live SSTV just fine on the HF bands (read LOW BANDWIDTH). So what you want to do is build two transmitters; one for audio, the second for the "audio" produced by SSTV, let's say at 700kHz. On the receive end tune a second AM radio to the 700kHz signal and feed this to the input of a computer soundcard. The SSTV video can then be displayed on the computer screen.<p>If you don't want two transmitters then there is another option; the VIDEO PHONE. You will sometimes see these being used by news networks to get video back to the studio from far off places where satellite trucks simply do not exist. The bandwidth of these phones will easily work over a carrier current signal, at least for one way signals. But these can be made to work two way as well.<p>If you want two-way signals with a video phone build a transmitter for each end. Then you will need to use a device called a phone patch "hybrid". That is another project all of its own.

[rshayes]

This sounds like a wireless intercom. The simplest workable approach is probably an FM signal. Power lines are noisy, and you might have to choose a frequency where the noise is lowest. Since you mentioned 50 Hz, you are probably not in the US, but you probably have the equivalent of the Federal Communications Commission. They will restrict the amount of signal that can be radiated, so your power level may be limited to fractions of a watt. <p>Isolation from the AC line is a matter of safety. Any capacitors used for this should be rated for use on an AC line. The value will be relatively small, but the capacitor won't be. Most probably, it will be a ceramic capacitor rated for over 1000 volts. Further isolation can be obtained by using a coupling transformer. This only has to carry the high frequency signal. The secondary can be series resonant with the isolation capacitors. This will allow the value of the isolation capacitors to be lower, and will give some degree of impedance matching. This can be a step down transformer. The line impedance is likely to be low, and the transformer will provide an impedance step up. The secondary winding should be well insulated, possibly with two independent insulation systems, such as insulated wire wound over a layer of tape or paper insulation. Depending on the frequency, the transformer could use either a powdered iron or ferrite core, and possibly an air core at higher frequencies.<p>The basic idea is to use small value high voltage capacitors to provide some isolation from the AC line, and then use a transformer for a further level of isolation.<p>[ October 21, 2004: Message edited by: stephen ]</p>

[Bernius1]

If you're using HF for audio, take a look at this:
ADC / DAC delay line
It still has to be decoupled, but it's a novel encoding approach. You'd just need two clocks to separate Tx & Rx. I'd like to encode speech as a courier-.rtf file, & output it at the serial port. (see fig 2). Like text encoded .bmp files.

[eoinitb]

anyone got some sample circuits or any suggestions on where to llok

[redrocker]

Try this.

[Chris Smith]

I think BSR? in your part of the world [GB?]invented it. Seeing that its over 30 years old, you should be able to contact them for just about every data sheet thay have printed over the years.