This post will be used for further updates, and photos.
A cheap backlight upgrade solution has always been on my mind. I even tried a lightbox using 6 120VAC compact fluros.. and while they gave good results, they produced far too much heat.. and it was bulky as hell.
Previously Considered idea:
I've thought about LED arrays, but even then.. you're looking at a stiff 100$, on something that might not work. (I was told heat would be a major issue)
The new intent:
So I figured, if you can't beat em. Join em. CCFL tubes are popular with manufacturers, so why not just increase the number like crazy. Insted of having just 25cm of CCFL tube behind the screen, why not put 145cm of it?
I've just ordered up two of these sets of CCFL tubes, with dual output inverters. Inside the little acrylic tubes are 290mm x 3mm ccfl blubs with ~29,000mcd light rating, and a 30,000hr life expectancy. I read a few reviews, and apparently the bare bulbs don't even get warm to the touch.. so I don't think heat will be an issue.
Pros: They're cheap (3.5$/Tube), they include 12v inverters, and they're very close to the right size (3mm) for embedding in the monitor.. only a half millimeter off, which I think should be feasible. They're fairly bright, and they have a long life.
Cons: They require bending modification in order to make them fit in a standard 7" LCD.
Bending the tubes:
I've already practiced with bending 2.5mm sealed CCFL tubes using a candle flame, and its much easier than you might think. The gases inside are at no risk of being damaged by candle flame.. the only risk really, is bending the tube in a way that causes obstructions inside, or closes it off.
I'm going to bend the 290mm CCFL tubes in their middle with a 1cm gap, and round curve, using a 1mm dowel and 16mm semicircle jig for bending and spacing purposes. Using two sets of these CCFLs will give me 8 lines of light going across the LCD panel spaced ~1cm apart. Its also possible to maintain the original backlight in this manner.
In order to fit the bulbs in, the thick clear difusion layer will have to come out. In order to maintain some phyiscal strength in the lcd, I'm going to cut up the thick clear flat chunk from the panel into strips that can be super glued inbetween the tubes, to keep them from being crushed if weight is put on the LCD. If the clear flat chunk is not quite thick enough, I'll get a slightly thicker peice of lexan to make the strips.
The only part I really haven't thought of is how I'll control the dimming. The original backlight will be dimmer, since the clear thick diffusion layer will be gone, but I think(hope) it will still be bright enough for use in the dark. I find I typically turn it to about 65% in the dark, anyways. If its at least 65% as bright as with the peice removed, then I could just put the addtional backlights on a manual "Light Booster" button, which would activate the two dual inverters, and 4 extra CCFL tubes when needed.
Alternativly, I could make a little dedicated device using Curiosity's Cario usb digital/analog I/O interface chip and code to control the backlights based on the reading of a light sensor. This would be kinda handy because it could also be used to only turn the screen on once the computer was running, or once a certain temperature was attained, based on a temp sensor reading. It could be used with the light sensor to activate only one of the inverters in mid-light situations, and only activate all of them in cases of bright light.. really, this option would make the positbilities for control endless.
Wish me luck. Shoot me down. Give advice and suggestions, or ***** me out for returning to a heated topic - I want to hear it.
This post will be used for further updates, and photos.
Also, something I'm unable to find.. What are the specs of the stock backlights in Xenarcs? I'm thinking it must be ~850vrms, 5ma, and ~35,000mcd.. but I'm not sure. Thanks to anyone that knows this!
hmm bending the tubes. post pics ASAP i wanna see.
still working on the upgrade btw. jsut suppliers holding it up
as for the turning on different tubes - jcdillin and I looked at that as an alternative. It could work but i would be worried about bright spots.
i think a better approach would be to get some xenarc inverters and as the xeanrc tubes are L shaped 2.6mm and about 280,, long get some similar tubes and then you can control the dimming using a contorl voltage into the inverter.
I already threw out the tube I had practiced bending (it was burnt out), but I'll try to get as many photos as possible when I bend the new ones. You would be amazed how easy they bend with just a few seconds of turning over a small candle flame.
I actutally found a very interesting (CHEAP) inverter on ebay... the vendor only want 3$ each, and they appear to very very well suited for 7" lcd sized CCFLs (They use 5v rather than 12v, but thats nothing a small 5v regulator can't solve)
It seems they're very well suited for dimming by voltage reduction, actually. Taking 2.5 - 5.5v, plus they're very strong (epoxy encased). The VRMS output is 1100v and the current output is 5.4mA.. Seems like they'd be good inverters to work with.. I also ordered up a few of these (the seller has hundreds for 3$)
no no no, you cant use voltage reduction to do dimming
you need to use pwm into the tube as if you reduce the input voltage the output voltage drops and you get to point where the tube just goes out.
some iverter use a pwm input to control the dimming, some have the pwm onboard allowing you to use a 0-5V control voltage.
I know dropping the votlage works.. might not be the best way, but it does work.
Those ebay inverters I linked to use PWM input to control the dimming.. I'm not very familiar with PWM devices.. Looks like I've got some (r)searching to do.
Those ebay inverters you reference are for optrex monochrome 320x240 1/4 vga panels. they use a small lamp.
The specs on that inverter are 1100 volt Start up, and 345 volts constant. Your Xenarc lamps probably require 1200+ volts startup, and a constant of 850+ volts.
PWM (Pulse Width Modulation) dimming will require the use of a seperate control board that will provide the required max input voltage for startup, then switch to allow for dimming. This is done by pulsing the input voltage to the inverter, not by controlling the output voltage. You can't just drop input voltage to the inverter to control brightness. If you were to wire the inverter to remain at constant start up voltage, you will heat up and kill your lamps, and possibly start a fire.
May I suggest going to EGR's website and poke around. They have all of their spec sheets online, and they explain in great detail how to control a PWM inverter, and what will happen if you don't do it right (read: FIRE).
Inverters are not a toy, and should be experimented with using caution. I am not saying you don't know what you are doing, just giving a word of caution.
RE: ccfl bending. I would assume you already know that the ccfl contains small amounts of mercury. If you were to crack a lamp while bending, you will release this and it may be absorbed through your skin. Mercury poisoning is something you should take seriously.
Also, consider this. A ccfl is gas filled under vacuum. You might create "flat" spots when you bend the lamp, since you are actually stretching the lamp. This might create spots on the tube that will be dimmer than the rest. A ccfl that is shaped by the factory is done so before they are vacuumed and filled, and for a reason.
Just my 2 cents, since your first post asked for input be it good, bad or ugly.
Good luck with your project.
I read the part where it said "Min VOUT" in the datasheet, and figured that to be, well, the Minimum power output! :P Now I see the low RMS power output.. what a bummer =\ Itd be interesting to find an inverter with a Very high possible startup voltage (1600v+), that changed its startup voltage based on a temp sensor reading.. 0c(1200v) -10c(1400v) -20c(1600V) and so on. This would solve the problem of screens not starting in freezing environments, wouldn't it?
I looked around ERG's site a bit, they have some nice units for sure, I was checking out a lot of JKL's products as well (easily sourced from Mouser).. and figured I'd check ebay. I thought I'd struck gold with these little inverters! :P Ah well, the CCFL tubes I've ordered come with matched inverters, so I'll be ok in that regard.. just less to play with, really.
For the bending, it really is easier than it sounds, you just have to go slowly, and be careful.. I'm pretty sure that the tubes will be dimmer at the point of the bend, but they should still conduct the power needed to illuminate the rest of the tube.
As far as the mercury goes, especially in tubes these size, theres little need for concern. If I'm to fear this much mercury, then I better not touch tuna. An incandescant bulb being powered by a coal power plant causes the release of many times more mercury into the envrionment than a ccfl ever will. :P I do very much appreciate the sentiment for safety, though.
I thank you for being frank, I'd much prefer posts that point out flaws, than simply "hey, cool! good luck!" posts.
Apart from the bending, this is basically what I'm planning to do and was just starting to research. I'd never thought of using cheap case CCFLs though! Very intriguing.
I have loads of space behind where I'm mounting my monitor so I was intending to build a light box with a load of CCFLs in it. 12" is probably pushing it even so but I'm not constrained by the size of the monitor & monitor casing.
Progress: 80% - Permanent install left.
Motion LS800 Tablet PC and dock.
Vista, Bu-535 GPS, RoadRunner, MPT2006.