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gork · 09-25-2003, 12:11 AM

iPal:

I ripped open my dash again tonight to take another look at this... I took apart the dash module where the dimmer is located. No luck. It's all electronic. On further inspection, this makes a lot of sense as the interior illumination is a mix of LED, EL backlighting, and Incandescent bulbs. It seems the illumination brightness is varied from 1-12V via PWM on the illumination wire, though I cannot 100% confirm that it is PWM since my multimeter reads true RMS and my oscilloscope is currently out of commission.

The problem I have with powering the inverter off of the Illumination wire is mainly that when the headlights are off, the wire is at 0V .. that would mean no backlight! also, at 1V the inverter would probably not even be able to power the CCFL.. I think what I really need is a circuit that somehow does this:

Illum wire at 0V -> Backlight powered at 12V
Illum wire at 1V (minimum dash brightness) -> Backlight powered at 5-6V or whatever the minimum voltage the CCFL lights at..
Illum wire at 12V -> Backlight powered at 12V

Unfortunately, I know only enough to be dangerous with circuits. I know there has got to be some simple solution to this problem, but I have no idea what it is :-/ This could help a lot of people too to have a workable way to dim the LCD backlight with the rest of the dash...

Again thanks for the help.. I wish my car had an easy solution like yours..

09-25-2003, 12:11 AM	#11
gork Registered User Join Date: Aug 2003 Location: Amarillo, TX Vehicle: BMW E46 M3 Posts: 655 My Photos: ()	iPal: I ripped open my dash again tonight to take another look at this... I took apart the dash module where the dimmer is located. No luck. It's all electronic. On further inspection, this makes a lot of sense as the interior illumination is a mix of LED, EL backlighting, and Incandescent bulbs. It seems the illumination brightness is varied from 1-12V via PWM on the illumination wire, though I cannot 100% confirm that it is PWM since my multimeter reads true RMS and my oscilloscope is currently out of commission. The problem I have with powering the inverter off of the Illumination wire is mainly that when the headlights are off, the wire is at 0V .. that would mean no backlight! also, at 1V the inverter would probably not even be able to power the CCFL.. I think what I really need is a circuit that somehow does this: Illum wire at 0V -> Backlight powered at 12V Illum wire at 1V (minimum dash brightness) -> Backlight powered at 5-6V or whatever the minimum voltage the CCFL lights at.. Illum wire at 12V -> Backlight powered at 12V Unfortunately, I know only enough to be dangerous with circuits. I know there has got to be some simple solution to this problem, but I have no idea what it is :-/ This could help a lot of people too to have a workable way to dim the LCD backlight with the rest of the dash... Again thanks for the help.. I wish my car had an easy solution like yours.. __________________ MY CAR IS FOR SALE! See My Project Page for Details - 2003 BMW E46 ///M3 Custom Dash Monitor Housing - OEM Fitment Custom Overhead DVD-ROM Housing in Headliner BMW I-Bus Integration My homepage with many other fun projects! Last edited by gork; 09-25-2003 at 12:13 AM.