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Remote sensor on powerline

Discussion in 'Sensors and Actuators' started by Tha fios agaibh, Dec 3, 2016.

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  1. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    I'd like to hook up a remote sensor at end of my driveway to alert when someone arrives.
    It's very far away from the house; about 500ft or 150m, so naturally I don't want to run a cable out there.

    Second option would be to use a RF transmitter but they can be prone to interference and it'd have to be adequately powered at that distance.

    Third option, I thought of was using home automation technology like X10, Insteon or similar that I believe communicates over power lines. I don't know if that'd be feasible at that distance.

    Oh, did I mention that I have a 120v circuit that's already out there for lighting?

    I've heard of power line communication (plc) where a microprocessor or computer can send data over power lines but don't know much about it and dont really need the bandwidth.

    Since I really only need one bit of data (on/off) to trigger a chime at the house, would it be feasible to use some kind of oscillator circuit to send a frequency and superimpose it on my household 120v 60hz circuit, then monitor that frequency back at the house?

    Thanks in advance for advice and guidance.
  2. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    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.
  3. Bluejets


    Oct 5, 2014
  4. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    Hop, thanks for the great explanation. I agree that if it can be purchased for ~$50 it's probably not really worth the trouble of building one.
    @Bluejets that circuit is awesome, I'm wondering if it will work on 60hz, or if its prone to false trips because it doesn't work at zero crossing as Hop discussed?

    That might be a fun one to build but would it work over 500ft?
  5. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    Thank you Bluejets for that circuit but I couldn't get it to work.
    I believe my transmitter portion is working ok because I can hear the high frequency when I apply 12vdc.

    The receiver portion doesn't seem let enough voltage through for it to work.

    I believe I followed parts list and circuit as video shows but something is obviously wrong.
    Any ideas where I went wrong?
  6. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    20161228_231557.jpg 20161228_231646.jpg
  7. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    From top of 1k resistor to bottom rail I only get 1.25v. Vce is only 0.5v
    I need at least 1.5v to turn on the triac, right?
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