Mobile monitor IR transmitter problem

Discussion in 'The Projects Forum' started by BoltsRUs, May 5, 2008.

  1. BoltsRUs

    Thread Starter New Member

    May 4, 2008
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    Hi All,
    Newbie Alert! I did a quick search and didn't see anything that might have addressed this before, so here goes:

    My car's flip down monitor has a built in IR transmitter, located on the lower right edge of the screen (odd in itself since they're usually near the release latch on the base). It barely works and is highly directional-you almost have to be in a straight line and close to get any audio to the headphones. My kids in the back seat can't get any sound sitting on each side unless they lean in toward the middle:eek:. Hoping it was just the cheap headphones I have, I tried another better set out of my minivan. Same deal. So I'm guessing it's the transmitter from the monitor. I have not taken it apart as of yet and am not really eager to do so, but is this something that can be replaced without scrapping the monitor? I don't have any real experience with IR circuits or troubleshooting so if anybody has any ideas that would be great. Thanks-great site btw.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Do you have a digital camera or a cell phone camera? You'll be able to view the output of the IR emitter with it. Try putting on a music video, where the music is fairly consistent volume (or has a consistent bass beat) so that you can get an idea of the projection pattern by moving all around underneath the screen to see where it's the brightest.

    It's possible that they used an incorrect part for the IR emitter; like a narrowly focused LED instead of one with a wider radiation pattern.

    Perhaps you could build an IR repeater; basically use an IR receiver, a power op amp, and a few high-intensity IR emitters. I've never tried building one, but I don't see why it couldn't be done.
     
  3. BoltsRUs

    Thread Starter New Member

    May 4, 2008
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    Thanks Sarge,
    I'll have to try the camera trick. Not sure I follow you as far as seeing the pattern-hopefully it will make sense once I do it.

    This is not a high-end video monitor, but it has a decent picture. I'm thinking (hoping) you may be onto something with the LED issue. That shouldn't be too tough of a swap, right? Is there a special LED to look for, or would my local radio shack/Frys know what I need?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Hmmm - Fry's - I used to love the store in Manhattan Beach. ;)

    Thing is - if you open it up, the warranty is out the window. What I'm thinking is build something that will amplify the existing signal, and re-radiate it where you need it.

    I'm rooting around in my stuff at the moment - I know I had some IR detectors and LEDs around here somewhere. Then my spouse decided to "clean up". :eek: :rolleyes:
     
  5. BoltsRUs

    Thread Starter New Member

    May 4, 2008
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  6. SgtWookie

    Expert

    Jul 17, 2007
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    Trouble is, that IR LED doesn't have specs on how wide the pattern is!

    I actually have some of thouse around here. I'm still looking to see where in the heck they are. When I find them, I could give you a better idea, because I could test them right here.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Ok, found them and tried one out. I wasn't terribly impressed; it didn't seem to be a whole lot brighter than the one in my TV remote control, even when I was running it at 100mA.

    The radiation pattern is stated to be 45° on the package, which seems to be a bit conservative - it's probably more like 55°, which would be better for your application. Of course, waving it around while I'm looking at a single sample through a camera really isn't terribly scientific or a valid statistic sample, either.

    The package further states that it's maximum current rating is 1.2A - but it didn't make it even close to that; it gave up the ghost at around 300mA. They probably meant on a short duty cycle - but there WAS no duty cycle mentioned.

    Getting back to your situation - I suggest that replacing a single IR LED isn't going to solve your problem:
    1) They're usually pretty narrow in their radiation pattern.
    2) The IR LED currently in the monitor has unknown characteristics. Simply sticking a different LED in there may make things worse, so that it doesn't work at all.
    3) You still won't be able to aim the thing.

    That's why I suggested an IR repeater to begin with. Advantages:
    1) No dissassembly of the existing unit is required; minimizing risk of damage.
    2) An external repeater could be designed to aim the IR pattern right where it is most desired.

    But then again, maybe all you really need is some sort of a reflector, like a small mirror or even a sheet of paper or a 3x5 card taped to the bottom of the monitor to bounce the existing IR illumination off of. It's worth a try - what's the investment? A 3x5 card and some invisible tape?
     
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