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How to Backlight an 83+
Posted by Michael on 1 May 2008, 20:57 GMT

Michael Hespenheide has created a new guide for backlighting an 83+. His plans are more advanced than most because he incorporates a photoresistor so that the backlight automatically turns on and off based upon ambient lighting. All power sources and wires are also kept inside the calculator, making this one of the best backlighting solutions seen to date.

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Re: How to Backlight an 83+
Aaron Miller  Account Info

That's pretty cool, I've never considered the photo resistor before, very clever. I did something similar with my ti85 before it got bricked by leaky batteries, but I installed a switch, and like an idiot assumed that the screen would diffuse the light well enough for all practical purposes, it doesn't.

I've seen some other schematics for this kind of thing before, I think a mixture of this one, and instead of plexiglass, using the screen diffuser glass from a Game Boy Advance I saw used in another type of installation would probably give you the best and most professional results you can get.

Very well done, and thanks for this article Michael, it was definitely worth reporting on. :)

Reply to this comment    1 May 2008, 21:25 GMT

Re: Re: How to Backlight an 83+
Nathan Ladwig  Account Info

hmm, the photos of the calc in the case is an 83+, but isn't the calc you're prying the screen off of an 84+? did TI change the board layout of the new 83+'s, or am I just mistaken?

Reply to this comment    3 May 2008, 06:46 GMT


Re: Re: Re: How to Backlight an 83+
mhespenh  Account Info
(Web Page)

You are correct sir. That is the screen from an old (broken) 84+ I used as a "dry run" before I attacked by (working) 83+. I forgot to snap pictures of the 83 while I was working on it, so I went back and took some pics of the 84+, since I already had it apart and the screen assemblies are essentially the same (aside from the main board changes)

Reply to this comment    3 May 2008, 19:53 GMT


Re: Re: How to Backlight an 83+
El_Diablo  Account Info
(Web Page)

Now would this apply to any 8X calculator or just the 83 or 84? The 89TI would look stellar with some sort of backlighting. Now I believe that a sheet of plastic that can perform total internal reflection like a normal backlit screen would work too, such as salvaging the screen layer off a Game Boy Advance SP. The lighting isn't through enough when just using plexiglass.

Reply to this comment    15 May 2008, 13:20 GMT


Re: Re: Re: How to Backlight an 83+
mhespenh  Account Info
(Web Page)

I can think of no reason why it shouldn't port to any other 8x calc.

And yes, there are definitely better materials to use than plexiglass, if you can snag something better, absolutely use it. I was trying to work with common (and cheap!) materials.

Reply to this comment    15 May 2008, 19:25 GMT


Re: Re: Re: Re: How to Backlight an 83+
El_Diablo  Account Info
(Web Page)

Hmmm... Fiber optic sheet strips work wonderfully! And it is incredibly thin and you only need 2 LEDs instead of 4.

But I found out that cell phone chargers with Mini USB shouldn't be put into the USB port of the 84+... completely fried it.

Reply to this comment    16 May 2008, 15:12 GMT

Re: How to Backlight an 83+
Brandon Wilson  Account Info
(Web Page)

"the backlight automatically turns on and off based upon ambient lightning."

I knew it was possible...could it handle 1.21 Jigawatts?

Seriously, though, this is a really neat project. I'm almost tempted to try it myself.

Reply to this comment    1 May 2008, 23:20 GMT


Re: Re: How to Backlight an 83+
Nikky Southerland  Account Info
(Web Page)

And here we thought you were dead!

Reply to this comment    5 May 2008, 17:48 GMT


What?
Michael Ride  Account Info

?

Reply to this comment    5 May 2008, 20:26 GMT


Re: What?
Duncan Smith Account Info
(Web Page)

Yes, Brandon isn't dead. It's an inside joke; you're not expected to understand it.

Thanks for posting!

Reply to this comment    14 May 2008, 17:45 GMT

Re: How to Backlight an 83+
mhespenh  Account Info
(Web Page)

mhespenh here,

If ya'll have any questions or comments feel free to shoot me an email or PM (mhespenh AT mhespenh DOT net).

Reply to this comment    2 May 2008, 03:13 GMT


Re: Re: How to Backlight an 83+
jesse frey  Account Info

Nice job I like how the photo resistor pokes out the case, in the photo it almost looks like an extra button.
if you powered the photo resistor voltage divider off of Vswitched then you could eliminate a transistor from your circuit because it would turn off when Vswitched turned off.

Reply to this comment    2 May 2008, 05:35 GMT


Re: Re: Re: How to Backlight an 83+
mhespenh  Account Info
(Web Page)

I thought about that, however the easiest place I found to tap into was a transistor on the calc mainboard which only provides +2V. I was worried about drawing too much current away from it. Using the battery as the power source ensured I didn't pull too much current away from other places it was needed.

Reply to this comment    2 May 2008, 06:02 GMT


Re: Re: Re: Re: How to Backlight an 83+
mhespenh  Account Info
(Web Page)

Wow, actually, now that I think about it, thats a pretty good idea.

I might work up a schematic and post it as an alternate circuit. I hope you won't mind if I credit you?

Reply to this comment    2 May 2008, 06:08 GMT

Re: How to Backlight an 83+
Boxknife  Account Info

I adapted these plans for my TI-86. Got everything working -great-, except I accidentally sliced part of the ribbon cable right as I was going to put the thing back in the case! Noooooooo :'(

Reply to this comment    11 May 2008, 12:34 GMT

Re: Re: How to Backlight an 83+
Brandon Wilson  Account Info
(Web Page)

Noooooooo...

At least you got it working, though.

Reply to this comment    11 May 2008, 19:29 GMT


Re: Re: How to Backlight an 83+
Duncan Smith Account Info
(Web Page)

How does the cut affect the display?

Reply to this comment    14 May 2008, 17:52 GMT


Re: Re: Re: How to Backlight an 83+
Brandon Wilson  Account Info
(Web Page)

If you had read the article, you'd know that cutting the ribbon cable destroys the display!

Reply to this comment    15 May 2008, 00:17 GMT


yes :)
Duncan Smith Account Info
(Web Page)

I know that, but he said that he only cut part of it. It's possible that, for example, it would result in a few columns of pixels going dead.

Reply to this comment    15 May 2008, 20:35 GMT

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