VWaddict

There's almost certainly a rather simpler way of dimming the dome light than the one suggested in that thread... (which would require a SERIOUSLY large capacitor)

Here's what I just drew up rather quickly:


The bit within the dotted line represents what's inside the dome light assembly; be it a VW or a Porsche version. There's a permanent live, a permanent ground and a switched ground. The switch either connects the low side of the bulb (represented in this version by an LED with a series resistor for simplicity's sake) to ground (thus lighting it up... -the high side is permanently connected to +12V), or to a switched ground, such that the bulb only illuminates when the pin switch in the door jamb is closed. (i.e. when the door is open.) The third switch position is in the middle, meaning that it doesn't light up at all, since the low side is then connected to nothing at all.

In the modified circuit, the high side of the bulb is still connected to +12V, the middle switch position still does nothing, and the 'permanently on' switch position still connects the low side to ground, but the third position now works differently.

In the 'door-activated' position, when the door is opened, the capacitor (C1) charges quickly through R2. The base of TR1 (a general purpose PNP power transistor) goes low, and TR1 is biased into conduction between the collector terminal (which is grounded) and the emitter terminal, which is connected to the remaining switch position. Thus the bulb lights up, since the transistor is saturated on, and connecting the low side of the bulb to ground.

When the door is closed, the door pin-switch opens again, and the capacitor is no longer held fully-charged. It begins to discharge through the base-emitter junction of the transistor, and the transistor slowly falls out of conduction. The bulb dims and fades out.

Sort of like the uber-simple "big capacitor" method of achieving the same result, but in this case the capacitor can be MUCH smaller, since the transistor does most of the work. If the transistor has a current-gain of 100, the capacitor can be 100 times smaller, so instead of 10,000µF, it need only be 100µF... -A VASTLY more manageable proposition, since capacity is directly proportional to component size (given the same working voltage) in capacitors.

Differences between this and a more-complex PWM circuit? Well, this one charges a 'tax' of about a half-volt, so the bulb is fractionally less bright when the door is open. Probably not visibly so, however.

the BIG difference though is that the rate at which the capacitor discharges is variable dependant on the load of the bulb. It will discharge MUCH faster with an incandescent bulb than it would with an LED bulb. Also, different LED arrays will also drain it more or less slowly, but the capacitor can be small enough and therefore inexpensive enough for a quick trip to your local 'Rat-Shack' to find a value which you may prefer, for as little as a buck or two.

Hmmm... I might have a go at this myself.

Keith

Alan

Actually that thread if you read it all - already showed a working soft on/off and delay module... no giant capacitor involved...? not sure where you got the idea that the giant capacitor was more than a fleeting thought (after all it was from AO!)...

Your design is a bit too simplistic to work well - fixed delay to dim ratio with too much on delay and no fine control over the dimming rate. The dimming rate will also be dependant on the supply voltage which is variable between about <12.5v and 14v depending on conditions.

Also consider that the dimmable load for the incandescents in an S4 is approximately 60W so you need a very large - low on impedance transistor & heatsink (not commonly available in a pnp).

Alan

AO

BTW, how my soft off circuit coming along Alan? I've got at least 4 months until I'll be ready to install it, so you still have some time.

Alan

Andrew - WHAT? - you haven't built it yet....?

I give you a perfectly good schematic and you just spend your time blowing-up your engine and taking your car apart again...!

Sheesh!

Alan

928ntslow

OK, I get it now, I was unaware of the previous thread.

It seemed to me that this was all the answer to a a question that was never asked. Rather than spending the next half hour reading that whole post, I will assume you essentially wanted better lighting, but opted to not use LED in the beginning. Plus, you liked the VW lamp housings. I had no issues making my originals work with festoons in different sizes. I guess you just didn't want to give up the gray housing look huh?

As for the dimming issue with LED's I think you're all crazy! I keep saying, LED's are more VIVID, not brighter. The brightest thing in my car is that dang LCD screen, which is nothing short of watching television in the dark. Thank God I have a one button dimming feature to douse the flame on that thing! SHEEEZ!

Bill Ball

Alan:

Did you try any of the high power 37mm festoons before you decided you needed to alter the lamp housing to accept longer festoons? I've used them - they are bright.
http://www.superbrightleds.com/festoon.html

Alan

Bill - I have tried quite a few differet ones - the good quality ones are expensive so I stopped looking after I founmd some that were bright enough. I find that most LED's are not really anything like as much light output as a 10W bulb. Its an apples & oranges comparison of course. The LED's are so directional they may appear brighter on axis but if they have a very narrow band its too all or nothing. Also the color temp makes comparisons very difficult due to subjective assessment of the look - no the brightness.

I have looked as some of the irregularly shaped types (e.g. wider than a festoon) - my concern was I wasn't sure these would fit the width of the fitting. I decided to go with what was easy and that I already had used & tested (and had enough on hand).

Alan

VWaddict

Alan,

I get it now... I started reading from the last half of page 5 onwards since that's more or less where you directed me, and never flipped back to the start of the thread. -As a result, the only two things I came across were the 'overly complicated' (your words!) IC-based version, and the 'overly-simple' (my words!) capacitor.

Yeah, it was a quick-sketch, intended to be something with about three components, which someone with only the most basic abilities might be able to source/assemble... I wasn't looking to include variable timing, etc. -Just a "find a cap-value that you like and shove it in there..." approach.

So an S4 has 60-Watts of dome lighting?? -Really?!!?? -Surely not in a single dome-light assembly though... (since this would be a one-per dome-light thing if anyone were to build it). DAMMN, though... -60Watts of dome-lighting... No wonder you guys usually wear sunglasses!

Keith

Alan

Keith

No not per dome light (all 10W each) but 2 doors, 1 roof, 2 hatch, 1 CE panel + 2 x door ends @ 2W = 64W! (less on earlier cars...)

I would not propose to put this per light - you could - but is so much more junk hanging around in tight quarters and you'd want them all to behave the same (timing etc) or it would look a bit wierd. Its also of course much easier to install it all in one place - next to the relay (the pin switches drive the relay that drives the switched ground except on the very earliest models).

Another thought I've been kicking around... It would be nice to have a timeout on the interior lights. My expedition does this for the door mode - leave a door open & eventually all the lights go out. In the individual switched on mode it does not ever go out though.

If I were to build a localized version for each fitting - I'd want to intercept both ground and switched modes with a 10-15 minute timeout. The way the car is wired its unfortunately not possible to implement this centrally - though with slightly different wiring you could.

Alan

VWaddict

Yes, my VW also has a few timeouts, including the 'door-open-with-key-still-in -ignition' chime...

It stops chiming after two minutes, the reasoning being presumably one of the following:
1) If you didn't notice it after that length of time, you probably never will!
2) You've got the door propped open for a perfectly good reason, and are now getting annoyed by the chime telling you that the door is open!

There's also a GREAT one on the radio: You can turn the radio on WITHOUT putting the key in the ignition, but it times-out after an hour, so you don't just forget about it and leave it on forever...

yesss.... good idea with the central timeout/dimming jobbie... It looks like it'd be VERY easy on the 951 however. -On those the pin switches seem to be a 2-pole-to-common-ground design, with one activating the courtesy light, the warrning chime and the factory alarm, while the other (IIRC) seems to kill the 'power windows still active' mode (they remain latched-active after the key is withdrawn, until the door is opened.)

FWIW, the VW light doesn't fit in the 944/951 front dome light position: it's recessed behind the 'surface', and the recess isn't QUITE large enough to fit the VW 'bezel' inside. -The hatch light WILL fit... however, the bezel overhangs the wheelarch curve slightly in that application, and it's a little prone to being knocked if anything is in the hatch... -close though, and a good thing to try!

Hmmmm... maybe I'll try that dual-opamp/FET design as a delay/fade design on the 944... I don't have much in the way of SMT assembly at home, but I can knock up a quick through-hole PCB for it.

Keith

Alan

My radio works like that too - its a function of the radio not the car - usually.

The 928 windows stay active until the door opens too - but it is all driven from the single contact pin switches.

Sorry these lights didn't work out - I'd expect there are other VW lights that would be a direct fit - might be worth checking dimensions... lots of early sharing between Porsche/VW/Audi & lots of downstream dimensional compatibilities ensued...

Alan

Mads

do you hava any pictures of the vw interior lights installed ?
Looks like a mod i would like

Mads

VWaddict

Pics installed in a 928, in black:




..and yes, that really DOES look like a lot of dome lights!!!

The standard VW suffix for black interior parts is "B41"... Grey is "Y20" and almond/beige is "8YS". -If your local VW part guy can only get you the part number for the grey ones or denies the existence of black ones, tell him to do a price-search on the same part number, but with "B41" at the end, instead of "Y20".

The Golf/GTI was indeed usually supplied with grey headliners, but the (special edition) 25th anniversary GTI in the USA had a black headliner, as (I think) does the USA-spec "R32" (4-wheel drive GTI with a bigger motor).

Keith

Gary Knox

Yes, the black surround VW lights are a bit hard to find, but the grey and white ones are all over the place (eBay). Simple procedure to mask the lens, paint the surround black if you have a black headliner. The white marks shown above for off, on, etc. of course are black as well, but it's easy, push one end in for off, neither side in for on with open door, and other end in for always on. Used ones with the pig tail connectors are about $4-6 each.

Gary Knox
West Chester, PA
PS: Thanks again to Alan and Jim Mayzurk for originally posting this idea.

Dave H.

but why spray paint them when you can just order the black ones at the dealer? they're the same price.

and by buying them, they still have the logos on them...