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TX one byte at 1Hz on existing 12VDC wire? — Parallax Forums

TX one byte at 1Hz on existing 12VDC wire?

W9GFOW9GFO Posts: 4,010
edited 2011-11-28 08:33 in General Discussion
Anyone know of a simple way to pass some data on a wire that also supplies power? The existing 12VDC wire goes to a lamp. I need to put a microcontroller on the lamp and send it one byte a second. Running a separate signal wire is not an option. It only needs to be one byte a second. Less would be okay, absolute minimum is one byte every five seconds.

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-11-27 21:55
    How much current does the lamp use? Is there anything nasty on the power line, like alternator noise?

    -Phil
  • W9GFOW9GFO Posts: 4,010
    edited 2011-11-27 21:58
    Current is unknown, less than 5 amps. No there is no alternator noise, should be relatively clean but there is likely to be other electronics on other branches of the circuit.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-11-27 22:12
    If it were just the lamp, or if the circuit could otherwise be interrupted in very short bursts, something like this would work:

    attachment.php?attachmentid=87244&d=1322460729

    The cap keeps the bulb on during the brief, low-going excursions of the serial data.

    -Phil
    data_over_power.gif
    707 x 307 - 3K
  • W9GFOW9GFO Posts: 4,010
    edited 2011-11-27 22:39
    Thanks Phil, I was wondering if interrupting the power would work. I think it should not be a problem for this thing.

    I'm having some difficulty understanding what the zener is doing.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-11-27 22:49
    The zener is there to limit the data voltage to 3.3V, 5V, or whatever your logic level is, and to eliminate any negative-going excursions.

    Here's another idea that might work:

    attachment.php?attachmentid=87246&d=1322462959

    The on/off-keyed 38KHz carrier could be provided by an H-bridge, MOSFET driver, etc., driven from a Stamp or Prop. The transformer impresses it onto the power line as a small voltage fluctuation, which is picked up by the IRED that's closely coupled to the IR remote control detector.

    -Phil
    data_over_power2.gif
    607 x 253 - 3K
  • W9GFOW9GFO Posts: 4,010
    edited 2011-11-27 23:05
    Phil Pilgrim (PhiPi) wrote: »
    The zener is there to limit the data voltage to 3.3V, 5V, or whatever your logic level is, and to eliminate any negative-going excursions.

    What (bad) would happen if the resistor nearest the zener is a 10k and the zener is replaced with a 4k7?

    I like the second idea too.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2011-11-27 23:10
    What (bad) would happen if the resistor nearest the zener is a 10k and the zener is replaced with a 4k7?
    Probably nothing bad.

    -Phil
  • kwinnkwinn Posts: 8,697
    edited 2011-11-27 23:23
    Perhaps an adaptation of this circuit would work.
  • tonyp12tonyp12 Posts: 1,951
    edited 2011-11-28 08:33
    If you want to use the same 12v to power the mcu (with a 3.3/5regulator)
    and you use the first idea you would need to use Diode plus a Cap large enough to ride out the data low pulses.
    Could share the lamps diode/cap but a little risky as the lamp will suck that cap dry in less than a ms. (or get really large cap =$)
    So better make one separate for the volt regulator/mcu.
    And if you don't mind that the lamp may dim for a few ms you could skip large cap for the lamp.
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