Remote sensor on powerline

Yes, indeed. The oscillator transmitter injects about 100 kHz low-level signal onto the power line by capacitive coupling.

General Electric invented power-line carrier signaling, IIRC, and it works just fine. The X10 product line uses this same technology, somewhat improved by adding a wireless capability. The general idea is to use a low-valued capacitor to inject an ultrasonic signal burst onto the power line at the zero crossings. The receiver is also capacitor-coupled to the same power line at the other end.

The receiver listens for and decodes these ultrasonic signal bursts in synchronism with the zero crossings. The pulses are quite short, a few tens or hundreds microseconds duration, and by "listening" only at the zero crossings of the AC power line voltage the signal-plus-noise to noise ratio is much improved over simple random bursts of signal. However, you could try using a "continuous" carrier, turned on and off by the driveway sensor, without regard to where this occurs within the 60 Hz power line cycle, since there is little chance of it interfering with anything else on the power line. Such a simple circuit might be susceptible to "false positives" however, like when you turn your Vitamix on to make your breakfast smoothie.

I would breadboard the transmitter with a microprocessor used to generate a 100 kHz or so signal when the driveway sensor detects presence. The receiver could be something as simple as a narrow bandpass active filter tuned to the transmitter frequency and then rectified to operate your chime or a relay.

You can add zero-crossing signal bursts later to increase reliability and lower the amount of signal placed on the power line. And a microprocessor at the receiver end would allow you to detect the signal and operate the chimes through one chime sequence, even if the transmitter signal went away. You could even add a delay in the receiver response to guard against "false positive" indications.

For a really robust, multi-transmitter system, you could encode the signal bursts to provide sensor address and data information to the receiver from the transmitter(s), which would also allow a variety of control functions. But why bother (unless you just really enjoy "foolin' around as I do) when you can purchase this technology off the shelf for about fifty bux?

Be careful to use the proper low-valued capacitor to couple signals to and from the power line. Someone here pointed out that not just any old ceramic capacitor will do: it must be rated for power-line applications. a Y1 class capacitor is recommended. And some electronics experience is required since you will be working with power line voltages.

 

2 versions of over the powerline...one at 220v and one at 120V

http://danyk.cz/ovladani_sit_en.html