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Lilliput reverse signal wire doing something weird!

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  • Lilliput reverse signal wire doing something weird!

    I'm a little puzzled right now, I took out my monitor to do some work on it, but now, it seems when I touch the reverse signal wire, the monitor switches to the video2 by itself. Almost like it's picking up the electromagnetic charge from my body and being overly super sensitive!
    If I touch the wire with some electrical tape or anything non-conductive, no problem, but the minute I put my hand really close to the wire (Don't even have to touch it, even 3/4" away and the monitor switches.

    Does anyone have experience like this? I tried shielding the wire by wrapping it with electrical tape but that didn't help. I also removed the old small wire and replaced it with a bigger wire but same problem :-?
    I'd like to not have to replace the circuit board since I definitely make use of the rear view cam in my car. I'm worried if I put it back in the car, there's too much noise around the wire from accessories and the monitor will constantly flick.

  • #2
    You probably just need a pull up or down resistor - probably any resistor up to 10M Ohms - probably even a 0 Ohm (ie, short circuit) - I don't know if the Lilli Rev wire can go to GND or +12V but ity SHOULD be able to (since rev lights are either +12V else shorted to GND via the bulb(s) which is typically about 4 Ohms).

    Hence you can probably connect the lead to either +12V else GND (whichever does not select what you don't want) BUT wait for others to confirm unless you know the specs, else us a resistor or 3W bulb etc to +12V or GND.

    Maybe the Lilli is faulty tho I'm suspecting it's a FET input - tho it should have an internal (pull up or down) resistor to prevent such spurious triggering.


    • #3
      wow, nice! You really know this stuff. If this helps, I had it connected to the 12v wire on the reverse light. It worked. I still have to re-install it back in the car soon which will give me an idea if I have a real problem of if the environment wont require any mods. If anyone suspect it's best I fix this regardless then I'll do so.


      • #4
        ME knowing this stiff? Ha! I was simply guessing.
        But I did recognise a typical floating 'high impedance input' problem - ie, so sensitive that stray electricity can effect it. It is strange that it does not have an internal pull-down resistor to keep it off - as in normally NOT reversing - but maybe that has gone faulty. Otherwise it is a common design oversight - eg, omitting the (say) 1M resistor between a FET's gate & source that ensures it turns & stays off when there is no gate voltage to turn it on.

        And I bumbled thru... At first I was thinking typical inputs where you would add a pull resistance - maybe 1K or 1M etc.
        Then as I wrote, I awoke... The reverse input would be designed for the reverse light circuit ie - it's either at the full raw +12V (noisy +14.4V etc) that gets switched to the reversing lights, else not and therefore is grounded thru bulbs.
        Maybe that's what Lilliput assume. But if there's a bad connection or the bulb/s is/are blown, or maybe if you used LEDs instead of bulbs, then some sort of pull-down is required to prevent spurious triggering.
        But the point is that that input can obviously handle direct connection to +12V, and a 4 Ohm or lower connection to GND (ie, 2 x 21W bulbs etc).

        This reminds me of an IMO poorly designed cruise control. If LED brake lights are used with no parallel bulbs nor pull-down resistors or ballasts, it thinks the brakes are on and the cruise control disengages. Instead of specifying a pull-down resistor, the manufacturer has published a relay circuit that invariably blows fuses etc because it shorts the switched brake +12V to GND!

        Anyhow it sounds like definite fix.
        And I doubt that direct connection to GND (for NOT reversing mode) will cause problems. (If it did, Lilliput should state "not for reversing lights greater than xx Watts" etc.)
        Last edited by OldSpark; 03-14-2014, 04:50 PM.


        • #5
          Sort of bringing this old topic back. I just recently pulled my carpc out ... again...
          I was having an issue where the USB for the touch screen would not recognize. Everything else worked fine, as in, no flicking between HDMI and video2, when I placed the car in reverse the CH would switch to video2 and the video displays the image properly. But loosing the touchscreen feature is kind of a deal breaker, so I did some tweaking and couldn't get the usb to recognize. Eventually I unplugged the connector where the video1, video2 and vga is attached and my monitor started acting all crazy again going from HDMI to video2 really quickly. I'm not even sure what could cause this now, it's almost like when the video2 connector is in, the camera stabilized something from the connector, but as soon as it's unplugged the auto-switch goes crazy.