Post by dv52 (Australia) on May 15, 2021 9:04:52 GMT
I was sent an Email from a friend (who is an OBD11 user) in which he complained that the digital display on the dashboard (AID) and on the center MMI screen of his Audi A3 8V was too dim during daytime (particularly during cloudy days). His request was: is it possible to change the daytime illumination of these screens?
The description below answers this question for other forum members who may have similar needs.
To explain how to change the illumination of the digital instrument panel and the MMI screen, it’s first necessary to understand how this lighting is managed on cars like the Audi A3. Although it may not be obvious, the brightness of these screens (and other in-cabin LEDs and dial lighting) is constantly being modified as the ambient light level in the cabin changes.
Specifically, as the car encounters different day-time conditions (from bright sunshine to overcast days), the illumination of these screens increases as the ambient light level in the cabin increases and the opposite happens when the ambient cabin light level decreases.
The device that manages this process is a small photo-transistor that is embedded into the A3’s cockpit display at the extreme right-hand end of the fuel level gauge – see picture below:
For those who are not aware, a photo-transistor is a semiconductor device with a transparent housing. The distinguishing feature of a photo-transistor is that it’s “gain” (think of this as “amplification”) varies according to the intensity of light falling onto its body.
The tweak
The photo-transistor’s response curve to changing cabin light (ranging from the darkest the brightest day) is determined by a bunch of adaptation channels in the Dashboard module @ address hex17 as follows:
dimming_characteristic_curve_adjustment_internal_phototransistor
- X1 > 00 00
- X2 > 00 32
- X3 > 00 64
- X4 > 00 96
- X5 > 01 F4
- Y1 > 00 00
- Y2 > 00 32
- Y3 > 00 64
- Y4 > 00 C8
- Y5 > 00 FD
As shown, the photo-transistor has 5 x reference points throughout its adjustment range and these reference points form a type of X/Y axis response to create a "dimming adjustment curve".
I'm guessing,but I assume from the above format that:
- the Y values determine the actual ambient light level in the cabin (i.e falling on the photo-transistor)
- the X values determine the illumination level for various in-cabin devices at the corresponding Y value
- the X/Y number is directly related to the intensity of the cabin light level - so the lowest light level=0 and the highest light level=5
In terms of the tweak, it’s possible to change both X and Y values, but IMO it’s best to keep the Y reference points fixed as factory set and to only change the X values.
From my tinkering with the X values, I’ve found that for any single Y value:
- Increasing the corresponding X value darkens the illumination level of in-cabin devices
- Decreasing the corresponding X value increases the illumination of in-cabin devices
- The allowable range for the X values is hex00 – hex1F4 (i.e. decimal 0-500)
So, the tweak to increase the illumination of the 2 x screens is simply the process of choosing new, lower X values for the photo-transistor channels. Of course, any new curve can be chosen, but I suspect that the dimming curve as set by VW probably gives the best eye response to changing cabin levels – so I suggest that the dimming curve “shape” as factory-set is retained and that each of X values be decreased by the same proportion.
However, unless you are skilled at arithmetic in base 16 numbering systems, the problem with retaining the dimming curve shape will be that the calculation of the new X values is not easy - because these values are hexadecimal. To help with this, I provide the table below which lists the new X values for different reduction factors (i.e. reduction factor “2” halves the factory settings):
reduction factor X1 X2 X3 X4 X5
1 00 32 64 96 1F4
1.5 00 22 43 64 14E
2 00 19 32 4B FA
2.5 00 14 28 3C C8
3 00 11 22 32 A7
3.5 00 0F 1D 2B 8F
4 00 0D 19 26 7D
4.5 00 0C 17 22 70
5 00 0A 14 1E 64
Simply pick a set of X-values and apply them to the channels. If the effect is not to your liking, try another suite of "reduction factor" values - or use your own settings
A final word of caution – don’t be too aggressive in lowering the X values; if the chosen values are too low, the screen loses it’s contrast. This said, the tweak does work and from my attempt with this tweak - the 2 x screens are more easily read and the colors do appear to be more vibrant!!
And a last note - when the X values are reduced, there will be greater illumination also of other LEDs and dial lighting in the cabin (like the air conditioning dials and the center console dial)
Don
PS: If you do use this tweak, I am interested in the final X values chosen - please leave feedback
PPS: The security code for the tweak is 20103