924Board.org

[Finbarr]

Well, as promised a few weeks ago, here's an update on my attempts to improve the gauge illumination using white LEDs in place of the normal bulbs.

The picture shows a normal gauge on the left, with uprated (2W) bulbs in place of the normal (1.2W) versions, cleaned up and run from a 14V supply. The gauge on the right has eight 50 degree 1560mcd white LEDs mounted in a nylon ring running around the inside. It's hard to photograph, but after a bit of image tweaking you can clearly see the difference. It's a more "clinical" white than the slightly yellow glow you get from the normal bulbs, so it would need all the gauges done to avoid looking odd.



The downside is that these wide angle white LEDs are considerably dimmer and more expensive than the 20 degree versions you can pick up cheap on eBay (8000mcd, or even 10000mcd). I'm going to try doubling the number of LEDs using the brighter, cheaper versions and see how that works out. I know current consumption is fairly irrelevant, but the normal gauge is drawing 345mA (4.83W) while the LEDs are taking 89mA (1.2W).

Worth the effort?
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1980 931 (with the odd electrical quirk...)

[Finbarr]

And here's the second attempt - fifteen (!) 20 degree white LEDs and one ultraviolet LED illuminating the redline (thoughtfully printed on the face in fluorescent ink, unlike the rest of the markings). Visibly brighter, although as you can just see on the top right, the LEDs are still a little too far apart. In fact, the ones in the top right don't really do anything as there's nothing to light - it would probably look better without them. Current consumption increased to 190mA (2.6W, about the same as the stock bulbs would take).



What do you lot reckon - worth trying it on the speedo as well?
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1980 931 (with the odd electrical quirk...)

[Smoothie]

Looking good. I like the idea.
There's no substitute for having the results right in front of you to look at, but I think you're right - that upper-right quadrant would probably be better unlit especially in the second, brighter version and definitely once you do one gauge, all the rest would have to be done for it to look right.
Do they only glow at one level or will the cars' existing dimmer still change the brightness? Does the UV led present any danger to your eyes?
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Lizard]

one thing I would recommend is getting the face off scanning it into the computer, and then changing the colors either black letters w/ white background or visa versa and then print them on a sticker paper that is glossy and stick it over the old face and then reinstall with the white ring (or color to preferance) and it will look alot better
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3 928s,

[david_bryan]

Looks nice...total cost ???

[Finbarr]

Thanks for the feedback guys. Yes, they dim with the existing dimmer, although this can be altered to some extent - the LEDs are currently wired in pairs with a 330 Ohm resistor limiting the current to each pair. If they were wired in threes with a smaller resistor (around 220 Ohms) the dimmer would have a greater effect, and if done singly with about 560 Ohms it would have much less (but wiring would be a headache!). I'm trying to get a balance between allowing the dimmer to adjust the brightness and making them reasonably immune to changes in supply voltage as other electrical items are turned on and off. In principle, you could build a regulator circuit that fixes the voltage supplied to the gauges regardless of battery voltage, and run them off, say, 10 Volts - but that's probably overkill...

I'm going to remove the LEDs in the upper right quadrant - they're just distracting. Ideally, the ones lighting the rest of the face would be centred on the numbers themselves as that would get most light out towards the centre where the numbers are.

I had thought about reprinting the face in a different way but (a) I quite like them the way they are, and (b) I think a white background would look a lot worse. The problem is that the illumination comes through a narrow gap at the edge and has to be reflected off two surfaces to reach the face - with a white background, I would expect the edges to be very bright but the centre to hardly get any light at all. The black background avoids this because the edges are the only parts you want to illuminate. I did see some fluorescent ink cartridges for printers once - one option might be to print a new face with fluorescent green rather than normal green. And with a shiny surface, I would expect the black background to light up more than the matt background does at the moment and reduce the contrast. Has anyone tried those coloured dial faces that were on eBay a few weeks ago? I'd be curious to know the results.

No danger from the UV LED - because of its location inside the tacho, you can't see the light from it directly - only after it's bounced off three surfaces. You'd get much, much more UV from the average "black light" in a bar or club (or even normal daylight). If you're concerned, I don't think it would make that much difference to replace it with a white one.

Cost? The LEDs came from a bloke on eBay called photoelektric who seemed to have an endless supply - five for UKP 1.79 plus UKP 1.00 postage (regardless of quantity). They're 10,000mcd, 20 degree beam. The UV ones are from the same bloke, UKP 1.75 for five. Beware - there are some people selling white LEDs on eBay that look cheap but sting you for stupid postage charges! Sixteen LEDs comes to UKP 5.73 (about US $10.50) plus eight resistors (a couple of pence/cents each) and the nylon ring which was cut from 5mm stock sheet I had lying around. Pictures below show the assembled ring, lying face down ready to go into the body and also sat in the vice under test at a slight angle (it actually hurts to look at it directly - the camera was none too happy either!)



On with the speedo, then...
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1980 931 (with the odd electrical quirk...)

[Finbarr]

Done a first attempt on the speedo as well - this was a bit harder because of the size of the mechanism. The three mounts for the original filament lamp holders (only two of which they ever used for some reason) are much closer to the sides of the body, which meant cutting chunks out of the nylon ring and because I'd already drilled the holes for the LEDs it's meant three larger than planned gaps in the illumination, which is just about noticeable on the photo.



The rather botched ring:



I think I'll have a second attempt - just waiting for some more LEDs...
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1980 931 (with the odd electrical quirk...)

[Lizard]

the reason the 3rd hole was not used is on certain speedos the turn signal indicator buld sat in there and iluminated a blinker in the actual face
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3 928s,

[Finbarr]

Thanks for that Lizard - makes more sense now. The third hole was blanked off with a bit of tape on my original and the spare I got to try this illumination.

Anyway, last post for a while on this - fuel and temperature gauges now lit as well, two white LEDs for each one but the wiring is a lot more fiddly because of the way the cluster is put together. However, the LEDs can be fitted just behind the dial face to shine directly across the fronts of the gauges, making it much easier to get good illumination:



I still have to tidy up the other two to remove the dark patches on the speedo (probably by mounting the LEDs either side of the gap at a slight angle) and remove the illumination in the top right quarter of the tacho. Then I'll swap this set with the ones in the car and try it out for real.
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1980 931 (with the odd electrical quirk...)

[924guy]

very nice work!!! gotta love the new and improved led technology..great stuff!!
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Eric
78 924
82 931 SE "smokey"
99' VehiCross
Y2K Honda Insight
http://www.cardomain.com/id/924Guy
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