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52 Posts
Discussion Starter · #1 ·
Hello guys,

Ever since I got the car, I always wanted to have some additional ambient lighting in the door card trim.
I have been tinkering with it for some time now and finally i have something to share. I hope I can get peoples opinions on it.
Pictures say a thousand words so what I would like is ambient light in the places marked in red:
Vehicle Automotive design Motor vehicle Personal luxury car Vehicle door

I would like to make it very subtle, so not very thick, just a small thin stripe of light.
And my goal is to make it look like it came from factory like that. I think that otherwise it would look like a hack/cheap.

Everyone is probably familiar with the LED strips, they are used everywhere and are quite cheap, but they are quite big for this application.
I managed to find an LED strip that is much smaller and also comes with frosted plastic body to diffuse the light and make it light up evenly throughout.
Here is a picture comparing the two and showing the light diffuser:

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At the bottom of the picture you can see the smaller strip taken apart showing how small the LEDs actually are. The white piece is the light diffuser. The whole thing is wrapped in black tape that is reflective on the sticky side so the light is bounced back and is more intense. Pretty sweet. The small strip is 8mm wide and 2mm thick and can be cut to length.

And I forgot to mention, its also an RGB strip, meaning you can apply a different voltage to Red, Green and Blue lines separately, which allows you to mix colours and choose the one you like. It has 3 power inputs for the 3 colours and a common ground. The colour lines can be powered by 12v for max brightness.

I will only use red colour though, as it matches the light of console buttons in the car.

The idea is to power the strip from the same power source as the inside door handle illumination. It's a 12v source that dims together with the cluster brightness adjustment.
This source can be used also on cars that don't currently have the door handle illumination in which case the pin for it is still there in the door ECU and needs to be turned on via VCDS
This is pin 3 on the front doors and pin 1 on the rear doors ECU. The brown wire is ground in both doors.

So far, I have built a small routing table with a rotary/dremel tool mounted to it.
This will be used to cut a 2mm groove/slot in the door trim so that the LED strip can sit in flush.
I then cut a piece of acrylic using it as a test piece, and fitted a small length of the LED strip into it. Here is how it looks:

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My own door trim has the brushed aluminium finish, but I am not willing to risk cutting it up so I bought a cheap second-hand door trim set out of an A4 (A5 and A5 share these parts). The set I bought is a basic trim level set - just plastic and no aluminium or other inserts in it, so that its easier to route the grove in it. The plan is to wrap it in brushed aluminium vinyl later on, to get the original look.
The A4 also has an additional trim piece on the passenger side, above the glove box, so I will use that as my next test piece.

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I got my inspiration from this link, although it is in Spanish and the man used the larger LED strip which was a more invasive method, and I think he needed to cut up the door card from the inside to get it to fit.

52 Posts
Discussion Starter · #3 ·
Here is a picture with the light in the room turned off.
Its hard to show it properly on camera, so there is a backlit keyboard on top of the picture to compare the brightness to something else.
I think that if anything, it will need to be dimmed down when its in the car, and that's currently shown driven at 5v and not 12v, so it can be even brighter.

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52 Posts
Discussion Starter · #4 ·
So using the routing table I made, I went ahead and cut a slot on top of the passenger side A4 trim piece that I decided to sacrifice as a test piece.
I did a few passes until I got the right depth as I kept test fitting the LED strip. I then sanded the trim surface slightly and degreased it before wrapping.

The wrapping vinyl I got turned out not to be the best quality, as for example it is not perforated so some trapped air bubbles occurred.
I also managed to get some pieces of dust stuck between the trim and the wrap so they are visible in the bottom left corner. But its just a test piece so it will have to suffice.
I am not a wrapping pro, but apart from the issues above I think it turned out acceptable, and looks quite close to actual brushed aluminium.
I think if you didn't put the wrapped and real thing side by side, you wouldn't be able to tell. I have my centre console wrapped already and it went well with the stock door trims with real brushed aluminium.

I then glued the LED strip in place and the results are below. Personally I really like it.
The only negative I can see is that the profile of the LED strip does not match the curve of the top edge of the trim, so the corners stick out 1mm or so.
But I think the door trim pieces top edges have a sharper corner rather than a radius like this one, so it should be less visible and not stick out as much.
There is a piece of the LED strip wrapped around the back of the panel, that obviously will not be there, I just did it like that for the test and to power it in the easiest way possible.

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52 Posts
Discussion Starter · #5 ·
I also found another version of this small LED strip which has individually addressable LEDS, WS2812 exactly.
Whereas the current one has RGB LEDs all connected together, which means they all have to be same color and brightness.
These are very popular and Arduino libraries exist so it's easy to use and program. This allows me to make small animations with the LED strip.

I was playing around with it and so far, I came up with the following idea:
When the car is unlocked via fob, the strip gets power and turns on, first it does a startup animation which will be a swipe of light in both directions (kind of like a loading bar) and then dimms down to a set brightness.
Then when opening the doors, it will swipe one way and when closing it will swipe the other way.

The plan is to have the brightness really low for nighttime, so it's not distracting, and bring the brightness up during the day so that its actually visible. The input signal for distinguishing between these 2 modes can be taken from the door button illumination line. ON = nighttime and OFF = daytime.


52 Posts
Discussion Starter · #7 · (Edited)
I do agree its a very fine line. I checked what is out there and considered my options.

There is a light fiber that you light up from one end, but from what I saw it doesn't light up evenly throughout, and it is kind of a press fit into the gap between trim pieces, so that looks like a half-arsed job in most cases, as it doesn't sit flush with the trim.
Also in most cases the points where the light strip starts and ends look like the strip is a cheap add-on and not part of the car originally, so and that is something I'd like to avoid.
Example here: Video 1
Another example here: Video 2

You can also buy a set of trim for the B8 that is very similar to what I am trying to do (incorporates the light strip into the trim neatly and tries to make it look somewhat OEM) but the only ones I could find come in carbon look, and it clearly looks like fake carbon at that. It's also very expensive as the only option I found is a kit with other lights like door pockets etc.
Video 3

Here is my main inspiration, although me using thinner light strips will make it more subtle and better, I think.
Video 4

Speaking about tacky:
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52 Posts
Discussion Starter · #8 ·

I ordered more aluminium look wrapping vinyl with air release pinholes so hopefully that's better quality.
I have to wait for it to arrive so I moved onto the electronics side of things.

I used an Arduino microcontroller to drive the animated LED strip from the video above, but I chose to use the ATtiny85 for the real deal. It's very small and can be glued with double sided tape to the underside of the door trims.
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The arduino is a much more capable MCU compared to it, but in this project it does all I need it to do (not a lot to be honest) and the small size is a plus.
It also has an on-board voltage regulator so it can be powered by the cars 12v system even though it's made to run at 5v.

Like I said in the first post, the plan is to power it with the same supply that powers the internal door handle illumination. This means it will power ON when unlocking the car, and still stay ON for a few seconds after locking the car.
The only issue with that might be that the door handle light supply might be pulse width modulated to control brightness. I'm not yet sure if the ATtiny can be powered with a PWM signal, even at higher duty cycle. I'll have to check that out first.

Next is the issue of sensing when the door is open/closed or when to turn on day/night mode.
Door open = puddle light ON
Night mode = buttons illumination ON

I can tap into these wires and use them as inputs to the microcontroller to determine what to animate on the LED strip. However these are 12v and I need 5v input signals, otherwise the ATtiny will break.
The solution is to use a voltage divider circuit. Since it's a car and we care about safety, we should use an automotive style voltage divider that has clamping diodes as a protection during higher voltage.
At 12 V, the circuit will deliver 3.6 V to the Arduino pin which is a clean HIGH input signal. This circuit is principally for automotive use where the voltage input may routinely be as high as 14 or even 15 V.

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The safety feature here works like this, when the voltage is so high that after R1 it is more than 5.7v, D1 starts conducting (most diodes need 0.7v to turn on) and lowers the potential at that node, making it safe again.
From my testing, when Vin was 15V, the voltage at the anode of D2 was 5.12V, so still not enough to turn it on, so this protection kicks in at even higher voltages, e.g. voltage spikes.

I designed a PCB that has two of these automotive voltage dividers on it. The ATtiny will sit on top of it, and it will also have 2 connectors, one with 4 pins for connecting to the car (power, gnd and the 2 inputs) and a 3 pin connector to connect the led strip (5v data and gnd)
To manufacture 5 of them costs 3USD on JLCPCB so it's not expensive, but I will get it ordered when I confirm that the ATtiny can work with the cars supply.
If it turns out that the supply is PWM and can't power the ATtiny, I will look into it and probably add stuff to it to make it work.
The PCB is 45mm x 25mm in size, and most of it is empty space for the ATtiny. It's only 8 components after all.

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