TV comes on spontaneously

  1. DaveC426913

    DaveC426913 16,440
    Gold Member

    I just found out why the TV in my bedroom will very occasionally spontaneously try to turn itself on. I've experienced this before, during a lightning storm. A good close hit will sometimes cause the TV to try to come to life (it's twenty years old and makes a loud piercing twang upon turning on). There's no mystery that it's coming to life because remote sensor is being triggered by the same frequency as the remote. (The TV doesn't actually turn on, it just goes through the motions of doing so. It will also do this if you don't properly press the button, or double-press it.)

    Last night, though there was no lightning storm, it tried to come on spontaneously anyway. It's done this before. This time I was able to identify the cause: a passing streetcar. My bedroom window is about 50 yards down a sidestreet from the main streetcar line in our Toronto satellite town. The spark from the cable must have sent out a sort of EMP, including the freq used by my TV remote.


    Funny thing though, while the TV is now 20 years old, I presume it still operates on an IR signal. How could an IR signal pass through my walls? Or could it be strong enough to bounce in my window through a 90 degree angle?


    Oh yeah, the cordless phone also tried to come to life.
     
  2. jcsd
  3. That reminds me of the movie: "The Ring".
     
  4. Danger

    Danger 9,878
    Gold Member

    IR imaging devices can see through walls, but a TV sensor can't (unless it's one bloody powerful burst). Anyhow, that's not something that one would expect from a tram. Also, I assume that the Transit Authority has RF emission rules that prevent radio interference, the same as any other consumer situation. That aside, though, a remote control uses a coded pulse sequence, not just a flash of light.
    A 20-year-old TV pretty certainly uses IR for the remote; the old ones were ultrasonic, with a different pitch of tuning fork for each function. When you push a button, a little hammer hits the appropriate fork and an accoustic sensor in the TV detects it. I've never heard of a radio-control for that.
    I think that you're just haunted.
     
  5. mgb_phys

    mgb_phys 8,952
    Science Advisor
    Homework Helper

    It's not the IR that is turning it on - it is spike in the IR detector circuit.
    For some reason I never understood TVs tend not to be separately grounded (once got a nasty shock off a metal screen inside one) so they are sensitive to any ground spikes.
     
  6. DaveC426913

    DaveC426913 16,440
    Gold Member

    That makes more sense.

    So, it really is an EMP then? Much like from a nuclear bomb, writ small.
     
  7. mgb_phys

    mgb_phys 8,952
    Science Advisor
    Homework Helper

    Possibly if there is a loose wire or unterminated track acting as an antenna, but more likely to be a mains spike.
     
  8. DaveC426913

    DaveC426913 16,440
    Gold Member

    Oh, you mean through my household wiring?
     
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