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Are there certain kinds of LED(s) that should be used? Is there a certain way the LED(s) should be put? If yes to any of these questions, why? Also, where is a good place from the laptop to get power from for the LEDs? Can I get power maybe from before the CCFL inverter, which is close to the LCD screen anyway?

Update: Here are some links to a page by someone who actually did this: here and a writeup here. And another here and writeup here.

Update: What would be a good way to control the brightness? (to control it using the Fn- keys would be neat if it is easy).

radagast
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Abbafei
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  • Are you sure you have enough space in your laptop to do this hack? The hack that you linked to involved a desktop monitor, most of which have more space to work with inside. – MBraedley Sep 01 '11 at 12:24

2 Answers2

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The CCFL inverter will most likely run off ~20V. As long as you run your LEDs in such a way as to be able to handle that sort of voltage (multiple ones in series, series groups in parallel, current limiting resistor per series group), that should be fine.

As for the dimming? The CCFL invertor may be being fed with a PWM signal to set the brightness of the CCFL (Some use PWM, some use an analog voltage - you'll have to probe around). This PWM signal could be used to control the brightness of the LEDs by switching them off/on rapidly. Then you will be controlling it in whatever way the laptop is designed to have its backlight brightness controlled.

Majenko
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I just had a read of the link, quite an involved process with plenty of option for error.
With care taken (note mistakes made/reported in link, try and learn from them)it should be okay though.
I think the best LEDs will probably be hi-brightness white, like this 5mm is probably okay depending on the width of the CCFL holder (the thing he drilled holes in) otherwise 3mm is the other common size for leaded LEDs. Or jusy buy a (white) LED headlamp and nick the LEDs out of it, may be quite cheap that way but LEDs may have shorter lifespan if poorly made - Nichia are a reputable manufacturer.

You need to ascertain what voltage/(waveform if PWM as Matt mentions) you will be using, and design accordingly. Depending on supply voltage, options are to parallel them, preferably with a series resistor in each leg to limit LED current, or series with one resistor, or series/parallel. Look like he did something like this in the link, they are in parallel and I see no resistor or mention of current control, probably not "ideal" (note comment about firing one LED into his chest on over voltage, which is a reasonable indicator there was no current control in place :-) ).
Or you could consider a constant current white LED driver (probably some ready rolled modules on eBay also), which is a better solution as it will ensure the LEDs are driven correctly. If you set it up right from the inverter supply/control, the dimming will still work. The driver chips usually have an option(s) for PWM dimming.

Make sure heat is dissipated adequately also.

Oli Glaser
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