Power line comms X-10

**dalescnc** · - 29th November 2007, 12:52

Graham seems we have similar things in common ;-) just started on a project using to pic's 1 as a master other as a slave to control 6 relays to switch 12v lights on & off. Im limited to 2 wires gnd and positive. I have found the impedance of the supply voltage been a car batt. need to modulate @ app 11mhz in order to get the signal down the line. If anyone could share some light on this idea i would appreciate it no matter what

Many thanks
dale

**versatronics** · - 30th November 2007, 06:44

Hi Dale
Did you really mean 11MHz? This is very high for PLC although if achieved will give you good noise immunity. Yearsd ago i developed a PLC (power line carrier) remote control system for the coal mines, using the trailing 5kV cables the coal cutters drag begind them. It was infeasible to connect directly to these a) as it would require the intervention of an electrician and thus down-time, and b) safety/isolation issues. so I was face with a way of getting a signal into the cable, getting adequate propagation a nd of course daling with the huge noise problem from the thyristor drive syatems of the motor. There are 2 modes to propagate into a cable: bifialr - where you excite equal and opposite signals between the pair of wires - this is hardest to do but has less line attenuation; and monofilar where you exite all the wires togethher as a bundle against a earth reference. This is easiest to do with an inductive coupler of some sort and needs no connection to the wire. however to electrically 'space' the wires apart I had to go up in frequency, also to get above the noise harmonics I used 4MHz This is very much higher than the usual 120kHz type carrier. i know this doesn't help much but you might find it interesting to see that high frequencies do have a place. The modems were designed with discrete phase locked loops and use FSK at 9600b/s. -- I may still use something like this for my house!!