Backlight option for any HP LCD Calc?


Has anyone successfully added a backlight to the display of any LCD display HP calculator? I'm curious what models would be easiest to modify, and some ideas of how to do it.


Hi, at least for the 200LX there is a backlight option.

The following links may be of interest for you:



I never had a backlight, but I used to have an HP-41 accessory that plugged into a module port, and had a grain-of-wheat light bulb on a flexible stalk. I don't recally who made it, but I bought it from Educalc, so it can probably be found in one of their old catalogs.

Just what I needed, a way to drain the batteries faster. :-)



Were you referring to AME's "Port-X-Light"? I first saw them selling it in the dealer room at the Philly PPC Conference back in 1982. If I remember correctly, they even offered a bunch of different translucent covers for the LED, so it shined in different colors.

Jake Schwartz



I think that one was it.

My HP dealer back then offered me one of these,

but I decided not to take it...

Now it would be a nice addition to my collection.

However, we tried to make another kind of display lumination.

At one point, there was a company (ALBA) offering very small

lights (not LED) which would have fit inside the case

of an HP-41, left and right to the display pcb.

IIRC they got too warm because of their very small surface,

so we cancelled the project.

Do you have one of these AME X-Lights for spare?



Unfortunately, I only have one Port-X-Light to my name. The AME guys gave it to me for writing their Port-X-Tender manual.



Too bad.

I should have taken the offer from my HP dealer,

their price was about $15 per unit,

which may not be much today, but was much back then.

At that time I was collecting my money for an X-Functions module...



Here is an article showing how to do it to a TI.

I think most any LCD model might be so modified. The inclusion of extra batteries to power the EL patch might favor the use of larger models, however. (There's enough empty space in the graphic models that you just may be able to build the batteries into the case.)

My only concern (and maybe the experts could chime in): I know that at least some LCD displays require the use of polarizing filters (often incorporated as a plastic cover over the glass LCD itself) to render their images. If a reflective back includes a polarizing layer, then removing such a back would render the display invisible. But I don't know whether polarization has ever been part of the reflective back on HP (or other) calculators.

Let us know how it works out!



at least the HP OmniGo 120 has an interesting reflection sheet on the back.

Because the display of the OmniGo 100 was next to unreadable,

HP put something behind which once was called like a 3D display or similar.

IIRC it looked quite interesting, but reminded me more of a rainbow effect...

And the effect wasn't good enough to make the display really easy to read;-)



ALL LCDs use polarization to operate. When we were evaluating an LCD for an aircraft application, we found the polarization was such that if the pilot (or copilot) was wearing polarized sunglasses and tilted his head a little bit one way, the display appeared to go black. We called up the manufacturer to talk to them about this. They said they normally cut the polarizers whichever way gives the best yield, but they could make it whatever way we wanted.

There are different types of LCDs, and the character-only ones that are meant to give best contrast in natural light cannot be backlit. I just picked up one such LCD off my workbench here and shined a bright flashlightlight through from the back, and absolutely no light came through at all. None.

LCDs have come a long way since I had an LCD watch, but it too was made to have super good contrast in natural light (including full sun light), and its backlight was a grain-of-wheat light bulb at the edge, not the back, so it kind of shone across the LCD, not through it.

Having a dim LED above the display and shining a little bit onto the keyboard in the appropriate color might be valuable for darkroom work.

Edited: 26 Apr 2005, 2:04 p.m.


You're helping me remember where my unease came from . . .

Once upon a time, I had a Sharp scientific -- a ruler-shaped LCD model. Upon disassembly, I noticed that there was no circuit board behind the LCD. I had the notion that if I cut a window in the back of the calculator and removed the reflective tape, I'd be able to see through the display.

Well, it didn't work so well. Like you say, nothing showed at all. But I had previously noticed that the front cover was a polarizing filter, and by rotating it 90 degrees, I could reverse the polarity of the display (light segments on a dark background).

So, I took another plastic LCD cover from a four-banger and put that behind my fenestrated scientific. It then worked as desired.

But I found out that my desire was misdirected: I couldn't put the calculator on a table and use it, as I now needed "backlight" to see the display clearly. I had to hold it up with a piece of white paper in the background to make it legible. Very inconvenient.

The whole experiment came to a sudden end when I sat down with the thing in my back pocket, cracking the LCD. Too bad!

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