TI-H: Backlit screen WORKS


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TI-H: Backlit screen WORKS




>When I was looking at the keyboard on my 86, I noticed a foam outline 
around
>the screen that was about 1/8 inch thick.  I was thinking, maybe if I 
could
>get many 1/16 inch LEDs to go around the foam, maybe a backlit screen 
would
>be possible.  Just an idea, tho.

That is similar to what I did, but if you just shine the light on it, it 
won't cover the whole screen. Even if you do end up getting enough to 
light the screen, you'll drain your batterys fast and have a wierd 
effect with your pixels. There will be shadows and hard to view pixels 
that make it not worth the bother. You also have the GLARE from HELL!

I solved the glare by lighting the back of the screen and the problem 
with covering the whole screen with light was solved by using a thick 
diffuser.

It works great. 4-6, maybe less, LEDs will light your entire screen very 
brightly. It looks fine when the light is both on or off. It uses 
high-bright yellow LEDs that are easy to view (red is worst cause of bad 
shadowing and they make your eyes sore after a while. I couldn't find 
green ones that were very bright). The LEDs are about 20 mA each, but I 
combine them in a combination of both serial and paralel to spread out 
the 6v from the battery to all of them evenly.

The removal of the foam is difficult, but if you are patient and 
CAREFUL, you will beable to remove the foam that connects the screen to 
the circuit board. Once that's all removed, remove the foam from the 
back cover and the 1/8" foam on the front. Then peel the mirror off the 
back of the LCD. Put a plexiglass diffuder (front &/or back is sanded or 
scored to reflect light upwards to the screen from a source on the 
edge.) between the mirror and the LCD. Put in the LEDs allong the bottom 
of the screen and make sure you put insulating tape on the circuit 
board. then tape or glue the LEDs down. Connect the resistor and switch 
(variable resistor can be implimented as well). Screw the screen back on 
to the front cover, but not all the way. It won't completely screw down. 
No glue is used for any parts of the screen. The pressure will hold it. 
If your cover won't go on, see what is blocking it. DON'T FORCE IT. 
You'll break the screen or the display driver chip on the 82, 83, 85 CE, 
and 86. If you can almost close it, your best bet is to grind the LEDs 
flatter with a bench grinder. The knife sharpener on some electric can 
openers makes a nice hobby grinder as well, and you can probably find 
one easy. If you do grind the LEDs, dont' grind them so far that you 
damage the element and do NOT grind on the front. It neads to be clear 
and rounded to project the light well.

Direct any questions to richfiles1@hotmail.com

some of you may not want to mess inside your calcs, so I do offer the 
job for $35, including shipping & handling. I also turbo for free with 
any upgrade (if the calc can be turboed).

Thanks and I hope you try the backlight (good practice to try on a 
broken calc if you have one. You can easily take the LEDs and stuff out 
again. I also suggest that you use a very sharp knife on the foam and 
you take your time. I spend between 30 minutes to over an hour to remove 
the foam. It is easy to slip and cut the wires that connect the screen, 
and you CANNOT REPAIR THAT. That's why I lightly cut using repeated 
strokes. don't pull on the screen either or you'll crack it. You can try 
when you near halfway through the last piece of foam (2), but if the 
screen starts changing colors (like if you press it hard), then quit 
pulling. A little is ok, but use common sense. Don't pull if it won't 
come. cut more.

Good luck for all who try this!

Richard Piotter

E-Mail:
richfiles1@hotmail.com
richfiles@usa.net

The Richfiles:
<A 
HREF="http://www.geocities.com/SiliconValley/Lakes/5081/Richfiles.html">The 
Richfiles TI Page</A>
<A HREF="http://www.geocities.com/Area51/Lair/8510/Richfiles.html">The 
Richfiles Model Building Page</A>


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