# LED backlight retrofit



## Jax184 (Jul 30, 2006)

I'm working on an assortment of modifications to my HP Jornada 728 PDA, and the current one is an LED backlight.
Since I havent done too much work with LEDs in the past, I figured I should drop in here and see if any of you can help me.

The Jornada has a single CCFL along the bottom of the screen, which lights it in the usual way. It's powered directly by the 7.2v li-ion battery pack, and the inverter dims the CCFL at the command of the operating system. I'd like to replace this with a strip of white LEDs.

This brings us to the first question.
Voltage.

I've seen someone else do this to their Jornada, and they first upped the voltage to 40v to drive them all in series. Is this really the most power efficient method of driving them? Being a small device run by two li-ion cells, I need to be careful with power use.

The second question is the eveness of the light. I want the lighting to be as even as possible, else it'll get annoying fast. I'm experementing with the backlight diffuser to see what I can do, but it may not be enough. Would more, dimmer LEDs spaced closer together give a more uniform light output without greatly affecting power?

And lastly, whatever I build should still be dimmable by the OS so I can further conserve power.

Anyone think they can help me? Anyone have a suggestion to improve on the idea?


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## wwglen (Jul 30, 2006)

Use the SMJLEDs. They have the dome shaped to give a very wide beam angle.

wwglen


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