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Thread: LED Bulb Coding - License Plate Light Without Pulse Width Modulation Option

  1. #21
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    Sorry Gary, i misunderstood your previous post, and probably caused some confusion as well.

    Yes, it is the stop/tail lights that i am hoping to find some leds for, but at some point, will certainly use LEDs for the licence plate if i can find some that aren't too bright and so ill adjust the codes available accordingly.



    Last edited by jasons6930; 05-06-2017 at 04:01 PM.

  2. #22
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    When I added LED licence plate lights to my PQ35 based Octavia (1K0 937 087 Q) I had to check byte 17, bit 7 to remove the bulb out warning. It also stopped the cold diagnostic light check disco when unlocking the car.

    Byte 23, bit 6 was checked from factory and still is.

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  4. #23
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    Gary,

    I found the same screen as you...




    Would the Bit 5 be something that if unticked, would allow non Can led lamps to be used?

    It seems to be 'grouped' with Bit 6.

  5. #24
    Benevolent Dictator Uwe's Avatar
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    Quote Originally Posted by jasons6930 View Post
    Would the Bit 5 be something that if unticked, would allow non Can led lamps to be used?
    It seems to be 'grouped' with Bit 6
    No, Load Management has nothing to do with what light bulbs are acceptable to the module; it determines whether loads are shed as the battery's state-of-charge depletes.

    The only reason those two appear "grouped" is because bits 4 and 7 are undocumented and thus blank.

    -Uwe-
    The engineering problems are likely insurmountable. It would be like proposing to land a rocket booster section on a barge floating in the middle of the ocean.

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  7. #25
    Verified VCDS User GaryM's Avatar
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    Quote Originally Posted by jasons6930 View Post
    Would the Bit 5 be something that if unticked, would allow non Can led lamps to be used?

    It seems to be 'grouped' with Bit 6.
    No, "Load Management" is something completely unrelated to the lighting. If Bit 5 is activated (as it currently is), that setting causes certain control modules or components to be put into a type of power saving mode to try and preserve some power if the battery voltage falls below a defined Low Voltage Threshold (LVT) value.

    Bit 5 isn't actually "grouped" with Bit 6. It's just that there is no Bit 4 (or Bit 2 either) so it is an optical illusion that makes it look like some of the tick boxes are grouped together when they are all actually individual entities.

    EDIT: Looks like Uwe already answered the question. I was far too slow completing my reply and pressing the submit button

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  9. #26
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    Thanks guys.


  10. #27
    Verified VCDS User GaryM's Avatar
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    Quote Originally Posted by GaryM View Post
    Yes I do have actually have an oscilloscope although it's a mains powered one so it just means I'll need to reel out the extension lead. TBH it didn't even cross my mind to scope the output in each of the two modes so maybe I'll try and find some time do that and then post back the results once I've done that.
    OK, so I have spent some time analysing my license plate bulb circuit with an oscilloscope to see how the "License Plate Light w/o Pulse Width Modulation (PWM) [LED Light]" setting under Bit 7 of Byte 17 actually affected the voltage output to the bulbs (screenshots in post #1 of this thread HERE). My expectation was that with that bit set to 0 (unticked), I would see a square Pulse Wave Modulation waveform similar to that shown in post #15 of this thread by DV52 HERE. And with that bit set to 1 (ticked), I expected to see just a static unmodulated waveform. What I actually saw was a bit surprise and also a bit of a disappointment.

    With that bit both set and unset all I get is this for both modes...



    So just a static 12v output with no pretty square waveform on either setting. The oscilloscope screen resolution is set to 5v per grid square with the output trace being two and a bit squares up from the zero volt marker (the yellow arrow on the left labelled "1"). You can see by the measurements table at the top that the voltage fluctuates between 11.4v and 12.0v with the average voltage being 11.7v so hardly a PWM signal.

    I have no idea why this setting does nothing on my car. If the PWM option is enabled (unticked), then maybe a PWM signal is only produced if the license plate bulbs are dimmed to something below 100% brightness. However, there is no coding value available anywhere to set the dimming value of the license plate bulbs so there is no way for me to verify this.

    I've tried changing the Tail Light Dimming values (Bits 4-7 of Byte 19 shown in post #4 of this thread HERE) but if I set it to anything other than "00" (inactive), I just get a flashing Christmas tree light effect on my rear factory fitted LED tail lights, and the license plate connector just continues to put out a static 12v output.

    When I have a some more time I will perform the same analysis on my front headlamp bulbs. Now these I am expecting to output a PWM waveform. I guess we shall see

    People on here always seem to like pictures with equipment in so a few more below








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  12. #28
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    Gary: that's weird -are you sure that the PWM circuitry in your particular module doesn't require an actual load to function properly? I notice in one of your pictures that the scope probe is hooked-up to an open connector -looks like there was no LED attached when the test was done (perhaps?). Just a wild guess, but LEDs are current driven devices, so it's not a far-fetched suggestion that a load might be needed to get the PWM circuits to fire-up.

    Don

    PS: nice test equipment - I'm envious!!
    VW Golf MkVII (MY13) - A3 8V hatch (MY17)

  13. #29
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    Gary,

    Could it be that PWM is only active when the system voltage is above 12V,to try keep the bulbs at their nominal 12V instead of the ~14V (that would shorten their life) when the engine is running and the alternator is charging the battery?

    -Uwe-
    The engineering problems are likely insurmountable. It would be like proposing to land a rocket booster section on a barge floating in the middle of the ocean.

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  15. #30
    Verified VCDS User GaryM's Avatar
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    Quote Originally Posted by DV52 View Post
    Gary: that's weird -are you sure that the PWM circuitry in your particular module doesn't require an actual load to function properly? I notice in one of your pictures that the scope probe is hooked-up to an open connector -looks like there was no LED attached when the test was done (perhaps?). Just a wild guess, but LEDs are current driven devices, so it's not a far-fetched suggestion that a load might be needed to get the PWM circuits to fire-up.
    Don: There are 2 number plate bulbs which both run from the same BCM pin (C27) and if you look at my second picture you will see that the other one is still fitted and illuminated during my tests. Keep in mind I still have incandescent bulds in my car at present and not LEDs (yet). So if a load was required on the BCM pin then that one should be drawing enough current. Certainly with a single incandescent bulb fitted and the cold diagnosis switched on for the license plate bulbs, I don't get a "bulb out" warning triggered for those bulbs. That only happens if both bulbs are removed.

    Next time I drag all my test gear back out I will certainly try putting a bulb on that connector and do another voltage test in PWM mode, even if just to rule out that as being a reason that I'm not seeing a PWM waveform.

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