FIX for LED problem

Reply Subscribe

Thread Tools

Search this Thread

Dec 22, 1998 | 04:30 PM

Rich Quinlan

Guest

Posts: n/a

FIX for LED problem

As some of you have noticed, when you install Stan's cool LED light, your sunroof no longer operates... Don't ask me why, since, as Stan pointed out, a LED is a diode, but you must add a diode to the circuit.Get a pkg. of 276-110 They are labeled 50v, 1amp micromini silicon diodes. Cut your power wire going to the LED, and solder the diode (with the band closer to the LED) inline. I don't think it really matters where the diode is (before or after the resistor). I connected mine to the LED, and the other side went to the resistor FWIW. This will ensure current flow only TO the LED, not both ways... What was happening before is that the resistor was dropping the voltage at the sunroof down to 2.4 volts, which is too low, and the sunroof wouldn't operate...this fixes it.Don't ask me why, but it works just fine... As my pilots say, "I don't care HOW you fix it, just fix it!" (Steve S., I knew you'd like that one)Rich QuinlanP.S. I wound up using two LED's in parallel with a 100 ohm resistor... the total light is the same as with one, but it's better dispersed, and the LED's will last longer. (Maybe 200 years instead of 100) It's not that bright at all... I may go for a 50 ohm..who knows..<ul><li><a href="http://home.att.net/~richquinlan">Quinland</a></li></ul>

Dec 22, 1998 | 05:35 PM

stanj

Guest

Posts: n/a

Online instructions reflect this recent fix

I would like to thank Rich for finding a cure for this problem. The problem was that the reverse voltage of the LED is the same as the sunroof voltage...I tested the setup now with the LED as mentioned on my instructions page, and with a 68 ohm resistor which is the lowest you can go. It works fine - both the LED and the sunroof.- Stan <ul><li><a href="http://rescomp.stanford.edu/~stanj/Audi/Dome/index.html">Updated red dome light instructions</a></li></ul>

Dec 22, 1998 | 06:59 PM

Chris Hlubb

Guest

Posts: n/a

Which type of resistor are you using?

I have found the 1/4W, 5% tolerance and a 1/2W, 5% tolerance, which is preferable if any. Also, I have a Radio shack catalog and they have some parts numbers that dont seem to match up. i have found a Red LED 3000mcd, 5mm part number 276-307, is this correct? Chris

Dec 22, 1998 | 07:07 PM

stanj

Guest

Posts: n/a

The never ending story :-)

Well, any resistor will do. 1/4W is more than enough: 20mA at 2V is 40mW, so you could feed a whole bank of LEDs of one of these resistors.The output of the LED is secondary - you need >1000mcd, as I say in the instructions, to have enough light. Anything above that you can always reduce with a bigger resistor.- Stan

Dec 22, 1998 | 07:21 PM

stevebrown

Guest

Posts: n/a

You guys ROCK...

absolutely, positively rock...Was just playing with the DMM on the circuit today, but all I could discern was that the voltage dropped a bit (with key in but ignition off) from 1.795 Volts to 1.785 Volts when both buttons were pushed.So that's as far as this chemE got...'til I see Rich's post.steve...rockin' to the music of Rich & Stan...!

Dec 23, 1998 | 12:28 AM

KevinL

Guest

Posts: n/a

Just wondering......

Instead of putting a resistor... can you put a little potentialmeter so you can adjust the brightness of the LED??

Dec 23, 1998 | 12:37 AM

stanj

Guest

Posts: n/a

Sure...

...but for that you would have to drill a hole somewhere. If I wanted to do that, I could have used the wide-angle LED projectors like the A6 uses. But I wanted to live with whatever I get.If I wanted to go nuts I could tap the power for the dash LEDs and wire that up to the dome light, but I really doubt that is worth the trouble :-)At any rate, do not go below the minimum resistance as described by my formula.- Stan