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Cheap LEDs for automotive dashboard application

Discussion in 'Electronic Design' started by Randy MacKenna, Aug 23, 2007.

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  1. I own a vehicle, whose designers had the wisdom (not!) to require that
    half the dashboard be removed in order to change the instrument light
    bulbs. Needless to say, I've gone many months with half my
    speedometer lit, and the clock completely dark.

    I'm about to undertake the repair, but before I plug incandescent
    bulbs back in, I believe I may be able to Rube Goldberg small white
    LEDs in place of the bulbs. I was thinking of these:

    Question: Am I kidding myself here, and just substituting one problem
    for another? Or, in an automotive application will these LEDs
    actually be more robust than the incandescent bulbs?

    I guess I'm worried that one >14VDC spike out of the voltage reg on
    the car's alternator, and these LEDs will fry. Maybe if I add a
    simple 12V regulator in front of them, that would do it (?)

    Also, will these dim okay with the car's dimmer control...or will it
    end up being an either "on" or "off" control?

  2. If the light bulbs on the dashboard are burned out, that means that the
    car is way too old. Get a new car.

    Vladimir Vassilevsky

    DSP and Mixed Signal Design Consultant
  3. Now there's a novel solution to replacing a light bolb that might not
    cross my mind too often. ;) I still have a 1979 VW rabbit working
    nicely, because I pull my own axles and replace bearings, etc.

  4. Rich Grise

    Rich Grise Guest

    Just give each LED its own series resistor, unless they come with them.

    Then, other than the fact that you have to watch the polarity, they
    should be virtually drop-in replacements, as long as you can figure
    out some way to plug them into the dash.

    Good Luck!
  5. Thanks...yes, I'm pretty sure I can get them placed/wired. I was more
    worried that they would have a reliability curve (in this application)
    that is worse than a standard incandescent bulb. My goal is to put
    something in place that will be very robust, since replacement is a
    very difficult task (on this car).

  6. in message
    Just get the $20 dollars or so of bulbs to replace
    everything when you have it apart.
    It'll last as long or even longer. There are long
    life bulbs that you can buy.
    Now the grain of wheat bulbs in radios thats a
    different story.

  7. I have never seen a car where the panel needed to be disassembled to
    replace the lamps. Sometimes its a bit of a chore getting your hand
    behind the panel, but the lamps are typically held in bases that can be
    removed with a quarter turn.
    Many vehicles use a simple rheostat in series with the panel
    illumination circuit for dimming. With this arrangement, the LEDs will
    not dim properly. They will remain at near full brightness until some
    point is reached and then dim quite rapidly.

    Some cars use a PWM dimmer. You could build one of these yourself and
    replace the dimmer rheostat, incorporating some protection against
  8. Rich Grise

    Rich Grise Guest

    Another thought just occurred to me - if the existing dimmer is just
    a rheostat in series with the +12 to the bulbs, then they might not dim
    the same as incandescents. But you'll have to poke around and find
    out about that.

    Good Luck!
  9. Jim Thompson

    Jim Thompson Guest


    My experience also. But you have to be a contortionist to get your
    hand in there. I typically lay upside down in the seat with my head
    under the dash :-(

    Many times I've found that "dead" lamps had actually been shaken out
    of the dash. They usually are single wire with ground return via the
    PCB copper clad in the dash panel.

    ...Jim Thompson

  10. Buy a new car? That just means that the job is too complicated for
    you, so you've thrown in the towel.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  11. ehsjr

    ehsjr Guest

    They laughed at me when I walked into the the parts department
    at the Ford dealership, disheveled, with blood dripping from
    my knuckles, carrying the radio, to get a new backlight bulb
    for it. I wrestled with that bastard of a job for a good long
    time before I got the radio out. Turns out that you can pop
    the thing out in a few seconds with a special tool, *AND* you
    can make the ^*%$*_ tool with a coat hangar. :-(

    The parts guy was nice enough to give me the bulbs for free.

  12. Jim Thompson

    Jim Thompson Guest

    Skinned knuckles are de rigeur.

    I recently bought a set of Japanese tools that allow removal of trim
    without bunging it up.

    Also read the manual on my truck... to remove radio, remove glove
    box... ta-da ;-)

    (I'm adding a new Panasonic "head" which has a Sirius port ;-)

    ...Jim Thompson
  13. Same here. 1995 Golf. First dashboard light went out after 10 years, so I
    thought that when I changed all of them (not just the burnt-out one) I
    should be good for another 10 years.

    So I spent $9 on new bulbs, half a year ago, but so far I've been to lazy to
    actually pull out the dashboard and do the work. Moreover, by now I can't
    remember where I put the new bulbs, so when the next light goes out and I'm
    forced to do the repair, I'll have to re-buy the bulbs.
    What I'm trying to say is that the technology used for lighting (or not
    lighting) the dashboard is a secondary, if not tertiary concern. How old is
    your car?

  14. neon


    Oct 21, 2006
    I hope you don't buy a new home because your lights burn out that is very funny. yes LED will outlast the incadensed lights. Do not worry about spikes ever the battery is a solid as you can get as a source. you never are going to spike a battery to not unless you have Boulder dam pushing it. the problem that you do have is LEDS needs minimun current and also minimum voltage to emitt a dimmer will work within a range then black out. If I was you i would put a quartz lamp somewhere where you can get easyly and use that only source to light up the whole panel by using platic lght conductor [ i cannot think of the correct name right now] and just route those pipes of beams to where ever you want and need. If you use LEDS you must install a resistor of the right value in series for each or even better get a current source for each. that gets expensive. if you use a quartz lamp then a dimmer is just a lm317 with a pot. design it as a current source and all you need is one pot for the whole thing. good luck.
  15. Thanks for all the replies. For the folks that can't believe the dash
    needs to be disassembled to change the instrument bulbs -- it's a 1997
    Volvo 850. You absolutely have to remove the top of the dashboard,
    and pull the instrument cluster to get to the bulbs. I have a pretty
    well equipped garage, and do all my own repairs (including pulling
    engines if I need to), and this repair job has me twitching. The only
    reason I'm doing it is because I have to also replace the AC
    evaporator on this car...which means (you guessed it) the entire
    dashboard, steering wheel, airbags...everything...needs to come out.

    Given the dimming complexities I think I'm going to abandon the LED
    idea. I just hope the replacement incandescents will last longer than
    the three years some of the originals did.

  16. Jim Thompson

    Jim Thompson Guest


    Ah yes, a Fluffo. You have my condolences ;-)

    ...Jim Thompson
  17. Rich Grise

    Rich Grise Guest

    My experience also. But you have to be a contortionist to get your
    hand in there. I typically lay upside down in the seat with my head
    under the dash :-(

    Many times I've found that "dead" lamps had actually been shaken out
    of the dash. They usually are single wire with ground return via the
    PCB copper clad in the dash panel.[/QUOTE]

    I once had a '75 Plymouth Gran Fury. I believe it was a one-owner, who
    had died of old age. You could almost stand up on the floorboards under
    the dash -- well, I exaggerate, but it was really, really easy to work
    on. Even fun, actually. The dash lights had inside-out sockets - that
    is, from the back of the dash you can grab each socket/holder and
    "bayonet" it out, and the bulbs were those pop-out-pop-in kind.

    When I had got it the tie rods were terribly worn so it kind of ate
    tires. It's an incredible feeling of accomplishment to swap out one's
    own tie rods, align the front end with a tape measure, and do tight turns
    around the parking lot without the front tires squealing. ;-)

  18. Rich Grise

    Rich Grise Guest

    Didn't somebody here tell this exact same story about a year ago? ;-)

  19. ehsjr

    ehsjr Guest

    If you can, put a diode or 2 in series with them and they'll
    outlive the car.

  20. In my Toyota FJ40, it is impossible to fit one's hand up behind the
    dashboard to access the lamp sockets. Fortunately, the entire instrument
    cluster is held in by two very prominent Phillips screws. Remove them
    (and a few plugs) and the entire panel may be brought to the workbench
    for maintenance.
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