Any ideas on how to transform my interior lights to

[aabdelhamid]

perform like the late models, I mean the dimming effect not simply on-off. Does this include any major changes or is it impossible.

[bahnstormer]

like when u close the door at night the lights fade off/out?

[aabdelhamid]

I need the dimming effect at night, way cool

[best535iever]

Hey great idea. Id love to do the same. It cant be impossible. Nothings impossible.

[George M]

yeah its completely impossible...lol...its just a relay. The best thing you can do with your interior lights is be seasonal. Around the beginning of December or so, I retrofit mine with twinkle lights to get in the Christmas spirit. Next I am considering mounting a small tree on the dash board but I am concerned about the water spilling out of the base during high speed cornering.
Your mileage may vary.
George

[best535iever]

So all you do is just replace relays? Sounds very simple. Shouldnt be expensive at all.

[bimmerd00d]

uhhh not that easy, it's gotta be a relay, and a series of resistors and capacitors. Where are the electrical gurus here?

[Dan in NZ]

If you added in a capacitor to the circuit, the lights would fade out when they are turned off, instead of turning straight off.

[Paul_540i]

Hi everyone, just registered. I recently picked up a nice 1995 540i 6sp manual (rare option over here in the UK).

In answer to your question, it can be done with a simple resistor-capacitor circuit in theory, but this would require quite a large capacitor and is not the way the standard systems work.

Likewise a relay wouldn't work on its own, it's simply an on-off switch (for isolating two circuits and switching larger currents etc).

What you need is a small controller that pulses the light on and off quickly. This gives the appearance of dimming as neither the bulb filament nor the eye react quickly enough to discern the cycles, it just appears dimmer. This is known as pulse width modulation. If you vary the ratio of the on and off periods, you can achieve full control of the brightness. 100% is fully on, 0% fully off, 50% half brightness etc. This is called the duty cycle.

You then vary the duty cycle such that when the light goes off it drops from 100% to 0% over several seconds giving the appearance of the light fading out.

I done a very similar thing with a previous car, it does look very nice. What you need is some kind of electronic controller to implement this. I used a PIC chip (a 16F627 with the appropriate code programmed into it), interfaced with some simple components so that it knows when the light input goes on or off. It then controls the light via a pair of transistors, to allow the high current of the light to be switched by the low current drive of the pic chip output.

I was planning on looking into this very thing on my e34. I haven't yet had time to check out the wiring setup, it's quite unusual in that the switch for the light in the front of the car also controls those in the rear. So there's obviously some connection there. Will let you know if I manage to get round to it successfully.

Cheers
Paul.

[Paul in NZ]

check out the wiring setup, it's quite unusual in
welcome to the club Paul I am sure you will meet Javier soon...............:)

[735guy]

perform like the late models, I mean the dimming effect not simply on-off. Does this include any major changes or is it impossible.
Obtain a General Control Module from a model car that has the "fading" lights, install it in place of your cars current general control module and that should do it.

[winfred]

the gm/rm from a e38/39.... are different then the ones in the e32/34


Obtain a General Control Module from a model car that has the "fading" lights, install it in place of your cars current general control module and that should do it.

[Javier]

but a relay in the RM, the relay switches on/off the interior lights. If you can ever fit the new GM in the old GM socket (which I doubt), you will not accomplish dimming lights.

Javier

[735guy]

the gm/rm from a e38/39.... are different then the ones in the e32/34
Winfred, If aabdelhamid is looking for his car's lights to mimic the interior lights of an E38/E39 then yeah I guess the GM wouldnt even come close to fitting. I guess I assumed he was referring to a later model e34 for some reason and even then the GM's may not interchange.

[grave77]

Electronicly u can do it, and its very easy ... 2 transistors and few small components. I already have this in my car ... u nead a simple decay circuit, usually we call it as RC trigger. check in the wen u should find it. if u didnt I can draw u a schematic for it. that goes for u all in Bimmer Guys :) .... Cheers

[Paul_540i]

OK Just swapped my DIY "theatre dimming" module from my old Audi onto the 540i. This uses the PWM control I described earlier to get the desired effect.

The BMW wiring makes it very easy. There are 4 wires going into the front interior light. +12V (red), 0V (brown), door switched 0V (grey) and finally the output for the rear interior lights (can't remember the colour). Don't rely on these wire colours though as I am in the UK so they may be different, check with a multimeter.

So I simply tapped into the +12V and 0V wires to supply power to my module. Then cut the door switched wire, and connected the car side to the input of my module and the light side to the output.

Now when the light is switched to "door" position, and the car signals for the light to come on, my module detects this and fades the light up. Likewise when the signal from the car goes off, the module fades the light off.

What's nice is that when the rear lights are switched to the door position, they are controlled by the switch in the front light. So if all three are switched to door position, they all fade in and out with just the 4 wire connections mentioned above. The map lights in the front can also be switched to door position and they too fade in and out :).

This setup is far easier than what I had to do in my audi to get the front and rear lights to fade!

PS The Audi had a nice feature where if you left a door open for 5 minutes it would switch the lights off again to prevent the battery being drained. I noticed the BMW doesn't so I added this feature to my module. When the light is switched on it starts a timer, if that reaches 5 minutes it will fade out the light even if the door input is still on. Of course I can change that time to whatever I want just by changing the code in the chip :)

If anyone wants the schematics and the hex file for the PIC microcontroller I'll be happy to forward them on. You do have to be handy with a soldering iron and have a PIC programmer though (these are quite cheap, less than £20 here for a basic one). Parts to build the module would be around £5 here.

Cheers
Paul.

[grave77]

Well PWM circuit is cool ... I just thought about it in a simpler way, I used a mosfet triggered by RC circuit and used the graye wire to trigger a transistor to keep it on when door open, the circuit was small to fit in the light compartment too and I added a pot to adj. the time decay. programming a PIC for this is way too much from my point ofview.
but I'm curious to know about urz too. plz e-mail me ur project I will be glad to see it.


cheers ....

[Dan in NZ]

My lights turn off if the door is left open for too long, but I think it takes about 20mins.

Couldn't a capacitor/s simply added into the circuit do the job of fading???

[Paul_540i]

My lights turn off if the door is left open for too long, but I think it takes about 20mins.

Couldn't a capacitor/s simply added into the circuit do the job of fading???

Maybe mine does switch off the light after the door has been open for 20 mins, I didn't wait that long to check.

The problem with just using a capacitor is that it needs to supply current after the car's supply has been cut off (to allow fading out). To do this even over a period of 1 second requires a significant amount of energy - think of the RC delay and consider that the resistance of the bulb is very low. Hence your capacitor would need to be very large.

grave77 I guess your MOSFET is voltage-following the capacitor in the RC circuit, basically using it as a reference? I will e-mail my schematics and C code for the PIC (I originally done it in assembler, the C is someone else's work which I reverted to as it's far easier to make changes).

The good thing about the PIC is that it's very versatile. This isn't really required in the BMW, but on some cars which don't have a delay for the light before dimming, or don't switch the light on when you switch off the engine, these features can be added. I even added a signal into the module from the alarm on my Audi so it would switch on the lights for 30 secs when the alarm was switched off - the alarm didn't provide this facility although most do. Just add an extra input from the ignition wire or alarm wire etc, and change the code to suit.

Paul.

[pundit]

yeah its completely impossible...lol...its just a relay. The best thing you can do with your interior lights is be seasonal. Around the beginning of December or so, I retrofit mine with twinkle lights to get in the Christmas spirit. Next I am considering mounting a small tree on the dash board but I am concerned about the water spilling out of the base during high speed cornering.
Your mileage may vary.
George
Yeah it took me a while to overcome that problem. Pesky water sloshes from the plant pot on the dash. I wound up fitting a gyroscopic auto self leveller to mine. Works a treat... not one drop spilled! ;)