Fix Odometer and LED light upgrade
 

After 27 years, the odometer gear finally let go last week. Since I have to pull the cluster, I might as well install LEDs and upgrade the lighting.

I have a couple of questions/ requests for advice/ request for comments.

First, should I go for blue, white or red? Any recommendations from those who've seen them? What looks best?

Second, I want to make sure the dimming works well. I can buy or build a PWM LED dimmer, but I want the existing built in rheostat/potentiometer in the dash to do the dimming.

I need to know the resistance of the factory dimmer pot. Can anyone tell me what it is? I'd like to build/buy the PWM dimmer, set it upon the bench for testing and modify or design it to use a pot that's identical to the factory pot to control it. Once I've got it working on the bench, I can install it. If I know the value of the factory pot, I can figure out how to make it control the PWM dimmer. So what is the resistance of that pot?

Thanks, in advance, for any info or recommendations.

For the color, I would go with either red or a white that resembles an incandescent bulb. Blue is one of the worst colors for maintaining some sort of night vision.
Dimming an LED will do only that, reduce lumens, the color will stay about the same.

As far as the dimmer resistance or tying the factory switch in with a PWM device, I can't help you there.

My buddy did his whole dash in red LED. He even took apart all the buttons and the heater controls and swapped everything out for red LED. It looks neat... too much work IMO for the end result, but it does look nice.

Personally I'd just go white. All the early Porsches were white backlit anyways. Red was always BMW. Blue is current VW.

And for what it's worth - I used regular bulbs but cleaned up the light tubes on the cluster and wrapped them in foil to reflect the light. Works great. Every bit as bright (in white) as my buddy's car is with his red LED's.

I have an extra odometer gear if you need it. Not sure of the tooth count off hand but I think there was only 1 or 2 PNs for the 944 Turbos.

For the record: I love the warm glow of incandescent bulbs. I repaired the mirror-y bit that diffuses the light and used new bulbs and it looks great.

have pics OmniGLH?

I tried blue and white. You can see blue at night. White is much better. Blue i found no better than stock.

Sorry cant see blue. Dam i- phone :)

No, I don't. It's rare he has his car out. Super super clean gorgeous car, so it only sees the light of day when the weather is perfect. Hell I think I only have ONE picture of his car despite me trying over the last few years to get him to take a few photos of our cars together - and that was only taken a few weeks ago when by some fluke he brought it over. The only time I saw the car with the lights on was because I was helping him dx a problem while the car was in the garage. I checked the lights out then. Didn't think to grab a photo.

This is what I did and I am very happy with the results. Not so bright that it impairs the night vision, but very easy to see.

I'd like to see a pic of the red interior lights as well.

I did a similar fix to what OmniGLH did except I used LED bulbs for the lighting. I got them from superbrightleds.com My first batch of lights didn't last that long but my last set has seemed to hold up pretty well. They can be dimmed and look great. I got cool white.

Do you have part numbers for the lights?

What are these bulbs you speak of?

:D

A while back I removed the bulbs / plastic reflectors, and connected 3 larger white led's right under the slot where the reflector light came through the cluster. Needed a bit of shrinkwrap and resistors to tap to 12v on the board. It worked surprisingly well, sort of a bluish tint from the led. Looking back I should have chosen red to match the gauges n stereo, but still works and is better than stock.

I find your project very interesting. I am also working on a similar project myself. I am in the beta phase of testing out a micro-controller based PWM system. So far my test circuit consists of a 350 ma driver that will power 3 cree xp-e and a micro-controller that PWM. I bought samples of warm white, neutral white, cool white, royal blue, amber, red, and deep red leds that I will test in the instrument cluster to pick the best color for our gauges. So far I am leaning towards the cool white because it tends to be a little on the blue side and should really make the orange needles pop.

I am also using an Arduino for the dimming. It compares the voltage drop from the original rheostat and then maps the values over to the led driver PWM. I need to find the right dimming steps and min/max values for the brightness but the basic programming of the controller is done.

I should be doing this in February so if you want to see the results or share ideas you can give me a shout. I was hoping to publish a kit that people would be able assemble themselves but components are somewhat expensive so I am not sure if it will be poplar. LED lights are hard to get right and using the original rheostat is a little tricky because it doesn't have a wide resistance range. Most people just end up using 5mm leds that they wire with a resistor but LED are constant current devices and a resistor only supplies a constant voltage. Since cars voltage range from 12.x to 14.x you end up sending different voltge to the led. Over drive the led and it burns up fast.

Also, cheap leds (from China for example) don't have the published run times and test have shown that they loose brightness and fail in as little as a few hours. The Cree leds I am using cost about 5$ each but they are rated and tested to last 50000 hours with a 98+% of brightness retention. They are made in the USA. The things that I still have to sort is the heat sinking and mounting of the leds in the cluster.

A lot of things can be done with the micro-controller. I could even use multicolor leds and you could change the dash color using the rheostat itself. An added problem to a micr-controller is that it needs 5v to run so you need a votage drop circuit. PWM led drivers are also looking for a 5 v signal so you have to use a LM7805 chip and be sure it doesn't over heat. I was actually looking into a circuit that would use a LM7809 then a LM7805 so that two chips are sharing the heat dissipation. These are the things I need to test.