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2005 SLK200K
107 Posts
Discussion Starter · #1 ·
There are two problems with simply changing the footwell ( and door access lightbulbs) to white LED bulbs.
1. when driving, they are dimmed by the car cpu, but they remain white, which is not in theme with the rest of the car interior accent lighting which is amber. The central console lights are lit amber. There is even an amber LED underneath the rear view mirror to subtly accentuate the dashboard amber.
2. They are dimmed but they are still too bright. The cpu cannot control the LED very well. They are a bit distracting to me. I notice my feet all the time when I drive.

for me its ok that the map lights, vanity lights glove compartment lights and others are white LED and bright. They are functional and you are indeed wanting to see or read something when you activate them. Footwell lights for me should be amber when dimmed (and are functioning as accent lights) and bright white when you are getting out of the car as they are acting as safety lights.
i had nothing better to do this easter weekend. Here is a simple bulb you can make that does exactly just that. i used a very common left over 5V RGB LED strip. 2 LEDs. Schematics are shown and lots of pics on how I built them. They work very well. Also they are properly dimmable. Components can be bought from you local electronics hobby shop. In Australia thats usually Jaycar or even Ebay.
For those who appreciate electronics read on. Else go ahead an see the pics and schematics. Some soldering skill is needed:
the reason LEDS dont dim very well is because, like most control circuits, the cpu uses PWM to dim the lights. LEDs use so little current that current is difficult to control. The diode resistor and capacitor in the input converts PWM into an actual steady voltage. When duty cycle is low (cpu is trying to dim the light) voltage on the capacitor is just enough to turn the red LED on and very very slightly the green one (which has to contend with one extra diode drop). Red + dim green = Amber. The blue LED does not turn on because its activation voltage is in the 3.2V area, plus the extra diode drop. The red led whose voltage drop is at 2.8V ensures this doesnt happen. (Green LED on voltage is 3V, it turns on very slightl, just enough to get an amber color). When duty cycle is high, voltage on capacitor reaches 8 volts and higher, ensuring all 3 colors light up which produces a white light, The 180ohm resistor is there simply to draw current as for whatever reason, the cpu shuts off the power if too little current is drawn.

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