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Hi GeekMan!
yes, I see that is a very recent post where LED strip was created from scratch... and resistors are used instead of a driver/constant currrent board was used... reduced efficiency though. I didn't see where he got the Leds.
To simplify, I used 9v fully assembled LED strips. The Jornada 720/680 on battery power only provides 8.5 volts max... so a boost converter is needed to obtain usable brightness
(as for bright outdoors
).
I might eventually design and build a 6 volt strip so that the boost isn't needed, but for peak efficiency a constant current driver still is necessary.
Presently, the cheap boost converter I'm using reverses the dimming control, dim is actually bright, and bright is dim which creates a few problems in WinCE mode
(auto-dimming feature actually gives super bright screen... so I disable autodimming
).
There is another LED backlight chip that allows reverse input so as to emulate the original CCFL dimming function... I bought a few and hope to build an LED driver that responds as original backlight did.
The difference with the LED upgrade is impressive as the old backlit screen looks dirty/dingy and dull... No true white... more grey-ish. However, the New LED are blue-ish tint... so the reds are weaker.
But the screen is uniformly lit now, and bright and crisp in appearance... looks "New" and pleasing and readable in any lighting even bright outdoors, and can dim down to almost complete darkness... something the CCFL could not do
(not much dimming range at all
).
With the "reversed dimming" LED driver there is an issue booting up Devuan Linux as it turns the screen off and stays that way... so I hope to get dimming back to normal. In the meantime, adding a line in Timo's Jornada-config app that sets screen brightness to mid range
(something like :
echo 100 > /sys/class/backlight/s1d13xxxfb/brightness
) turns the screen on as the desktop finishes loading.
In general, although not perfect as is, prototype, It is a vast improvement , looks modern instead of dull and worn out!
joval from his J720LED/WPAwifi/Raspi4/firefox hybrid HPC