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

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jasons6930

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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.



 
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langers2k

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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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jasons6930

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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.
 
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Uwe

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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-
 
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GaryM

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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 :D
 
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jasons6930

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Thanks guys.

:)
 
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GaryM

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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 :D

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







 
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DV52

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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!!
 
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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-
 
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GaryM

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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: 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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GaryM

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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-
Good point Uwe. I was just testing with the engine switched off because I was working at the back of the car and didn't really want to be breathing in lungfuls of NoX from the exhaust :D I did however have a battery charger hooked up to the battery (not sure what the voltage output of that is though because I didn't check). On my next analysis session I'll make sure I do a quick test with the engine running to see what happens. Will report back the results in due course :)
 
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jasons6930

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jasons6930

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Little video of single contact p21 LED stop/tail, with no adjustments (not that there are any).

LED in left, standard in right.

In the flesh, the LED in tail light mode is brighter than the standard lamp and about the same in stop mode.

The video just about pics this up.



Actual lamp used...



 
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GaryM

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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-
Good point Uwe. I was just testing with the engine switched off because I was working at the back of the car and didn't really want to be breathing in lungfuls of NoX from the exhaust :D I did however have a battery charger hooked up to the battery (not sure what the voltage output of that is though because I didn't check). On my next analysis session I'll make sure I do a quick test with the engine running to see what happens. Will report back the results in due course :)
OK, so today I did some further analysis with the "License Plate Light w/o Pulse Width Modulation (PWM) [LED Light]" setting to see what effect it actually has. This time I had both incandescent license plate bulbs installed and had the engine running. With the PWM setting switched either on or off, I just get the following waveform on the oscilloscope in both modes. Slightly higher voltage this time due to the alternator charging circuit running (min 13.2v, max 14.0v, average 13.6v) but still no PWM output at all. I have no idea why. Maybe that setting is actually redundant on my particular BCM :confused: I now have the LED festoon bulbs so I'll do some further testing tomorrow with those in place of the incandescent bulbs.



 
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Uwe

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Well that leaves me scratching my head....

-Uwe-
 
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GaryM

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Well that leaves me scratching my head....

-Uwe-
I guess it doesn't really matter because I don't want PWM for the LED bulbs I'll be fitting anyway but I always like to understand how things actually work so it's a little disappointing to have come to a bit of a dead-end with this but not to worry.

I have a few other things on today but if I get some time I have 2 Osram 36mm festoon LED bulbs to fit. These are non CAN Bus ones so don't have a huge heatsink attached to them like their CAN Bus counterparts :) It seems that they're not supposed to be used for exterior lights but tough because I already got them now so that's where they'll be going on my car :D

 
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jasons6930

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That's spooky as I was just about to push the button on a pair of those but in 4000k.

I watched a review of them on YouTube and they were impressed with them as they are not too bright and equivalent to around 5w output that the filament bulbs are.
 
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jasons6930

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After having a couple of days with the LED tail lights, they are a little on the bright side compared to the rest in the cluster, that are w5w capless lamps x 3.

As there is an option to activate tail light dimming, and that there is no dimming applied by default, would it work for me to drop the voltage to the rear cluster to reduce the brightness of the LED or would that also affect the w5w lamps as well?

I am (probably incorrectly) assuming the stop and tail lamp circuit is separate to that of the w5w's so in theory, they wont be dimmed if applied a change, but i am also hoping that by reducing the voltage, it wont affect the running of the LED tail lamp?
 
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OK, so today I did some further analysis with the "License Plate Light w/o Pulse Width Modulation (PWM) [LED Light]" setting to see what effect it actually has. This time I had both incandescent license plate bulbs installed and had the engine running. With the PWM setting switched either on or off, I just get the following waveform on the oscilloscope in both modes. Slightly higher voltage this time due to the alternator charging circuit running (min 13.2v, max 14.0v, average 13.6v) but still no PWM output at all. I have no idea why. Maybe that setting is actually redundant on my particular BCM :confused: I now have the LED festoon bulbs so I'll do some further testing tomorrow with those in place of the incandescent bulbs.
Gary: please excuse my ignorance where your car is concerned, but there is a PWM situation that does approximate to the DC trace that keeps showing-up on your scope: when the duty cycle of the waveform is 100%! It's probably a dumb question- but was there any form of dimming on the lamps that you used in your tests?

Don
 
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Keep in mind that UK legislation for vehicle lighting hasn't had any changes to it since 1989 so you probably won't be surprised to hear that everything regarding approval markings refers to "filament" bulbs with no mention at all about either LED or HID/Xenon discharge gas lighting because neither had been invented at that point in time. However, if you tried to argue the toss in court because your car has LED bulbs and not "filament" bulbs, I'm not sure if you would come out of it unscathed :D If you're interested, the legalities are under The Road Vehicles Lighting Regulations 1989, Regulation 14 HERE.

The UK MOT which is equivalent of the German TÜV but far less strict also has no mention of the test requiring the MOT'er to check any bulbs for approval markings. It is just a visual check to ensure that all light bulbs are working and are of a white or yellow colour, with a machine check to ensure that main beams headlights are correctly aligned (details HERE).

That probably explains why we have thousands of cars driving around in the UK with Chinese manufactured aftermarket LED bulbs fitted to them, none of which have any type of approval whatsoever, and where no-one in authority so much as bats an eyelid at them.


After market HID are supposed to be failed on the MOT test as most them have no headlamp washers or any self levelling devices. Plus, normally they're the chavvy little tikes that blind you when coming toward you or behind you as they have not been set up properly. I saw a set catch fire a while ago.........insurance DID NOT PAY OUT!!!
 
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