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Bright Future: Jornada 720/680 CCFL to LED upgrade

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joval Page Icon Posted 2022-04-01 9:09 PM
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Jake - 2022-04-01 11:04 AM

I'm telling you, Joval, if you had been on the production line, HP would still be making these things.

Jake


Jake: ...Sad but true... "I coulda been somebody, I coulda been a contender." ........ I think that if there exists a parallel Universe where such is the case, of course the device would HAVE TO BE NAMED the Jovalada720!!!??? ........joval via J720/WinCE/open_wifi_to_esp8266_WPA2/WRP_proxy/PIE4 (otra vez amigos)

Edited by joval 2022-04-01 10:26 PM
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C:Amie Page Icon Posted 2022-04-02 12:07 PM
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Jovalada 720 That might stick!
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joval Page Icon Posted 2022-04-03 4:17 PM
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FYI: I replaced the backlight in a Jornada720 with a new CCFL lamp and compared it to the LED upgrade. To my surprise the newer CCFL lamp wasn't much brighter than the old and the screen was difficult to see in moderate bright outdoor light... whereas the LED was very much brighter and easy to read outdoors with minimal shading, and even somewhat viewable with in bright direct sunlight. It's possible this is the norm for CCFL, but maybe the ccfl power inverter is weakened too and causing the poor result. The LEDS are a blueish white and the red color is lessened and there is a faint serration at the bottom of the screen due to the spacing of the LEDs. But overall it is a Marvelous Improvement!!!. ....................................joval via J720/WinCe /Esp8266_WPA2/ WRP_proxy/PIE4

Edited by joval 2022-04-03 4:23 PM
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joval Page Icon Posted 2022-04-08 2:53 PM
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Bit of a surprise after LED backlight conversion: Booting into Devuan/Linux the screen turns completely black like it's turned off. Thought I'd have to redesign the boost circuit... but not so.

Seems the default brightness setting is too low to fire up the LEDs... holding a flashlight aka "torch" up to the screen one can see the devuan image faintly. Since the Jornada-config window in present, by tapping on its position, then L for lcd, enter, then down arrow+ enter three times... backlight turns on. So default brightness needs to be reset higher and also increase and decrease need to be reversed because LED boost converter reverses things.

Bright screen is nice. Eventually I will learn how to change the boost circuit to be more like original CCFL inverter... I'm just happy things DO work in Devuan mode afterall... just need to add a startup script to reset the default brightness level on boot-up and tweak the Jornada-config some.

joval via J720/Devuan/WPA/RasPi4/Firefox

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joval Page Icon Posted 2022-04-09 5:20 PM
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FYI: Quick temporary fix... I just added a line in Jornada-config "echo 100 > /sys/class/backlight/sl13xxxfb/brightness" so now it boot up with dark screen until jornada-config runs and mid brightness screen appears.

I also changed the increment change from 50 back to near what Timo had originally, 10.

I will add that echo line to init.d or cron so it shows up earlier.

Eventually I will explore adding a bias circuit to the dimming Mosfet so the backlight won't go off like that. BTW on Devuan shutdown, no more white screen... instead completely black/off. Maybe this will lead to a fix for the white screen issue.


joval via J720/Devuan//WPA/SSH/RasPi4//VNCviewer Hybrid HPC
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joval Page Icon Posted 2022-04-09 11:03 PM
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Once you see the bright LED backlit screen... I doubt (m)any of you would ever suggest going back to dull lack-luster CCFL.

If a Good 'Silver'smith by his actions turns his "mettle" into something truly delightful and inspirational to others ... perhaps a 'Good Will' Smith should do likewise...

joval
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joval Page Icon Posted 2022-04-10 12:47 AM
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joval - 2022-04-09 9:20 AM



Eventually I will explore adding a bias circuit to the dimming Mosfet so the backlight won't go off like that.



Actually, perhaps a simple change to a logic level "Depletion Mode" MOSFET (full "ON" current with no dimmer input signal) from the present "Enhancement Mode" MOSFET ( completely "OFF" if no dimmer input signal/voltage) should get the bright/dim keys working correctly!

Could add a mosfet driver transistor to that if needed to increase or invert low voltage dimmer input high enough to turn on MOSFET.

Will keep you posted!

Joval


Edited by joval 2022-04-10 12:50 AM
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joval Page Icon Posted 2022-04-11 1:24 AM
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So far I have successfully LED backlight converted 2x Jonada 720's and one Jornada 690 and they are looking good. .....................................................Battery life does seem improved, as often I turn brightness down indoors as the screen is so much brighter...................................................................................................still working on the MOSFET circuit and learning as I go along...adding 2 resistors to bias the dimming mosfet show eliminate the Devuan dark screen on boot... just minor problems for most part .......... I will master in time...........................joval via J720_LED(WinCE mode!)/open wifi to ESP8266_WPA2/WRP_proxy/PIE4
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joval Page Icon Posted 2022-04-11 2:12 AM
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I just discovered that there are online "Circuit Simulators" that should be a big help. Up until now I've been using your friendly Automobile Mechanic's Approach: just keep throwing parts at the problem and hope it gets fixed!!
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CE Geek Page Icon Posted 2022-05-18 9:54 AM
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Someone got the same idea with an old Palm OS handheld that had a weak CCFL display:

https://hackaday.com/2022/05/17/led-backlight-brings-vibrant-colors-...
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joval Page Icon Posted 2022-06-04 2:16 AM
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CE Geek - 2022-05-18 1:54 AM

Someone got the same idea with an old Palm OS handheld that had a weak CCFL display:

https://hackaday.com/2022/05/17/led-backlight-brings-vibrant-colors-...


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
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joval Page Icon Posted 2022-07-04 2:57 AM
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Hi All,

I am quite impressed with the LED backlight upgrade overall... although I haven't worked on it recently and there are still some issues like the reverse dimming/intensity control in WinCE and completely dark screen during boot with Devuan Linux. This I know can be remedied with a better boost converter chip... but I'm just not all that motivated yet to grab the soldering iron and revisit the carnage of burned out transistors and ic chips which got me this far. So, still a work in progress, but quite adequate as is.

Also there is a little bit of "flutter" (no actual flicker) only when in the dimmest range, far dimmer than the CCFL was ever capable of (due to cpu power use as when listening to mp3 music play, etc).

Overall, I'm quite happy with it... I hadn't really tested it out much in devuan/RasPi/VNC mode until today... and I must say it is really a remarkable improvement surfing the net with such crisp bright images of items on ebay or Amazon.

It works very well in the home environment with WPA wifi and the RasPi4... anywhere around the house. The devuan images hosted on HPC:Factor are really slick and full featured but there is a degree of "gamemanship" in login into the RasPi, calibrating touchscreen, increasing screen contrast because the RasPi desktop is 2 steps lighter, stuff like that. But once you get it set up... it really is a "poor man's Cosmo" in so any ways... (except the $700 price and only being wifi not cell phone).

I'll be getting around to posting the circuit diagram hopefully in the near future... of this prototype that it is... and maybe someday a youtube video showing the entire process opening the case, removing the ccfl and power supply, inserting and orienting and securing the trimmed LED strip, mounting the LED boost inverter, etc.

There's that saying... "perfect is the enemy of good." Things are working "real good" right now... I just want it to be near perfect. If some of you will be happy with "good" then I've done enough... and the price is right... less than $20 to bring your J680/J720 screens literally "out of the dark ages".

best regards,

joval on his "poor man's Cosmo" : a J720/Devuan 32GB Image /WPC11 wifi WPA/ RasPi/ VNC/ Firefox


Edited by joval 2022-07-04 3:05 AM
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