924Board.org

[RC]

924guy wrote:

[pocketscience]

[2Fast]

[Peter_in_AU]

Finally got around to making up LED lighting for the instruments as described by Roger. I experimented with yellow LEDs ranging from 4k mcd up to 9k mcd and they all came out looking sort of a dull orange.

I ended up going with white LEDs. 7k mcd for the tach, fuel and temp and 3.5k mcd for the speedo and the console instruments. Interestingly, with 2 3.5k mcd LEDs in the speedo it is noticeably brighter than the tacho with 2 7k mcd LEDs. I had to double check the resistors and the specs on the LEDs to be sure I hadn't got them wrong.

What a difference. It looks great. Thanks Roger for the motivation.
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

[skemcin]

[Peter_in_AU]

They're not fused so before you start make sure you're getting power to your instrument lights.

Like all things the degree of difficulty depends on your experience.

If you haven't used a soldering iron before then making up the lights will be a bit of a learning curve only because the parts are small. I found the best way was to clamp the iron horizontally and hold the parts with two hands. A second pair of hands would make things easier. After making the first two the rest took me about two minutes each. You need to make 9 LED modules.

If the guy at the electronics shop can't tell you the correct resistor value or you're ordering online then find the specs for the LEDs you want to use and type "LED resistor values" into google to bring up lots of calculators to tell you what resistor you need. You just key in the supply voltage (13.2v to be sure) and the LED forward voltage (Vf) (1.6, 2.2 whatever) and the LED forward current (If mA). The calculator will tell you what standard resistor value you need.

Installing the lights means removing your tach and fuel/temp/warning (multi) instrument. You don't need to remove the speedo. The speedo lights are at about four o'clock and ten o'clock on the back of the speedo (looking from the back) and can be removed and installed by reaching through the tacho and multi-intrument holes. The first time you remove the instruments they can need a bit of pressure to get them to pop out. You could probably do it without removing the main instruments if you have really small hands and don't mind lying upside-down in the footwell. The console instrument cluster comes out reasonably easily but can be a real pain to put back in later cars.

When installing the LED module into the lamp holders I found it easiest to remove the holder from its loom connector and install the LED module on a bench. This makes it easy to check your connections with a multimeter.

A couple of notes;

On lamp holders with a spade connector the spade is connected to +ve. If you have soldered the resistor to the long (anode) leg of the LED then the module should be inserted so the resistor is connected to the spade.

For the multi-instrument there are a whole bunch of lights. You replace the one at the top (temp) and the one at the bottom (fuel). The holders come out by turning them 90 degrees. When you insert the LED module into these it doesn't matter which way you insert it. When you install the module and holder into the instrument if it doesn't work then take out the holder and module and turn the whole thing 180 degrees and reinsert.

The later oil pressure gauge and volt gauge have lamp holders that need to be turned 90 degrees to get them out. These lamp holders seemed smaller than the ones in the main instruments and I had to shave the veroboard slightly to get it to fit in.

Make sure the module is securely inserted into the holder. You don't want the module to fall out a rattle around inside your instrument. One of mine did and I had to disassemble the tacho to get it out.

After inserting each module into an instrument switch the park lights on so you can check that the LED is working.

Once done the instrument lights dimmer will only change the brightness slightly. If I can find another dimmer I might experiment with it and see if I can get a better range of dimming.

This is a great winter project and a real improvement in the lighting.
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

[sgloki]

Just a comment,.... I really like this fix and I might just try it your way...I happen to have a spare board sitting around I could build the circuit on.

Another method of doing this on low income andlimited technical knowledge....or utter lack of ability to follow these instructions:

Go to the local auto store and buy some of those ugly 12v cig lighter plug in type accent LED's in the color of your choosing. (schucks.csk.craigen.napa) all carry these in the U.S.

Remove the housing from the led's/resistors and install with a piece of frosted (or sanded down) plastic as a diffuser, then remove the cig plug and wire into your dimmer switch (or better yet rewire and solder). I did this with great success on a 88 vw fox. the led's don't really dim so much as turn on at a certain brightness, so it's mostly a on or off operation, but it can be done for under $20 USD if you use 2 accent light kits and already have a soldering iron and wire handy.
_________________
All work and no speeding makes jack a dull boy.

[RC]

Glad to hear you`re happy with the result Peter.
Good idea experimenting with various intensities to achieve a similar balanced illumination.

Regarding the dimming, I think the easiest practical way is to add a resistor in parallel with the whole loom to increase the voltage drop across the dimmer VR. Using 5W ceramic wire wound resistors as they`re common and cheap, and running at say half the rated power to keep heat to a minimum. This equates to around 68 ohm in common values. Higher (82 or 100 ohm) is fine but 56 ohm may not get too hot and at 47 ohm its displacing 4W which will be more than warm. Try 2 in parallel (34 ohm) between the black and brown wires at any convenient point. Some trial and error and a matter of perception since you don`t want the minimum too dim for safety reasons. Maybe get 3 or 4 (68 ohm) resistors and keep adding in parallel till you`re satisfied. Then let us all know. The maximum brightness won`t alter.

Keeping on the subject of LED lighting, I also replaced the interior courtesy light. After disappointing results from commercial replacements made a festoon type from the vero board, LEDs and end caps. That was OK until I came across this:

http://www.dealextreme.com/details.dx/sku.3871

Perfect fit in out lenses and a brighter white light than the stock 10W incandescent. Price includes shipping as well. Can take a pic if anyone is interested. A very pleasing result that you can easily read with or whatever else you may desire to do in your toofah that requires seeing what you`re doing.

[Martijnus]

could be I read over it, but how about the dimmer? can you dim the LEDs as good as bulbs?
I can't remember if leds are more like binaries....on/off....more like TL lights or you can vary their intensity.
_________________
"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment