The Museum of HP Calculators

HP Forum Archive 06

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Message #1 Posted by Chris Randle (Lincoln, UK) on 4 Oct 2001, 8:23 a.m.

Would anybody else, apart from me, find a backlight useful on a calculator?

Three reasons I like backlit screens:

1) Perfect visibility under less than perfect lighting conditions.

2) Usually improves contrast.

3) You can tinker in bed without needing the light on and disturbing other sharers of said bed. This is really the no. 1 reason for backlights, as all geeks will know :-)

There are few downsides. Cost/complexity is one. Battery life is a fair trade IMO because you can choose to use it or not as you wish.


Re: Backlight
Message #2 Posted by Vieira, Luiz C. (Brazil) on 4 Oct 2001, 8:49 a.m.,
in response to message #1 by Chris Randle (Lincoln, UK)

When I´m doing serious computations (99% of time), I prefer working on a very well illuminated workplace.

With computers, no matter: monitors have their own light. But I think of calculators as handhelding devices, so I can find always a better angle to read answers. Most of the time, the new models get to the computer to download files, so the display reading is not a must.

But in the field, generally speaking, they are (for me) often used under big amounts of light. So, backlight, if available, would be needed only in some sort of activities that are not so often available in a calculator.

Maybe the X-Pander would have it, cause it was a palm, not a calc, having many other utilities (appointments, for example, that can be consulted in any situation)

Re: Backlight
Message #3 Posted by Marx Pio(Patropi) on 4 Oct 2001, 7:58 p.m.,
in response to message #2 by Vieira, Luiz C. (Brazil)

Saw you talking about X-Pander,

I dowloaded a X-Pander Math from for E-125 Cassiopeia, and I discovered why [(hp)] gave up marketing the XPander...


Marx Pio

Re: Backlight
Message #4 Posted by Ellis Easley on 4 Oct 2001, 9:42 a.m.,
in response to message #1 by Chris Randle (Lincoln, UK)

As I understand it, LCDs have to be designed to be either front- or back-lit (has to do with how many times the light passes through the polarizer), but I have a very inexpensive (~$8) digital multi-meter that includes a switched backlight. It consists of two green LEDs, one near either end of the display, behind the panel. The light source is by no means uniform, you can clearly see the LEDs through the panel when they are on. (I have a 40 character panel mount display with backlight that uses about a dozen green LED dice and filter to produce a very uniform backlight) But the light is very sufficient to use the meter in the dark (3-1/2 large digits plus sign). I don't know if the mechanism at work is back-lighting or front-lighting from the light leaking around the plastic case.

It would be interesting to try an LED (or two etc.) located above or either side of a calculator display to provide a front-light, which is what a calculator display is designed for anyway. It could be rigged up as a clip-on accessory with its own battery. Red LEDs are most efficient but this might be offset by the fact that the eye has maximum sensitivity to green, allowing lower LED current.

Re: Backlight
Message #5 Posted by Andrés C. Rodríguez (Argentina) on 4 Oct 2001, 12:15 p.m.,
in response to message #4 by Ellis Easley

Once upon a time, the calculators had LED displays, so you can tinker in the dark... If you keep your calculator plugged to the mains during the night (on a bedside wall socket), it will:

* recharge batteries,

* be available to let you calculate, develop programs,

* just stay there, as a "pacifier" :-)


* "almost" (no BEEP nor time functions then) work as an alarm clock.

Since the high voltages are restricted to the AC adapter, there is no risk having a plugged HP25 in your bed, it may even work as a blanket warmer :-)

And you surely memorize the keyboard layout, so you can work/program/play without looking at the keys (something not possible with virtual keyboards, menus, etc.).

BTW, a display showing -8.8888888-88 was a good emergency flashlight substitute during a blackout!

Oh, the good old times

Re: Backlight
Message #6 Posted by Vieira, Luiz C. (Brazil) on 4 Oct 2001, 12:25 p.m.,
in response to message #5 by Andrés C. Rodríguez (Argentina)

I´ve never thought about that... hope the blackout does not rest for more than one hour.

Good reading some stuff this kind. Sent me back to my college times...

Re: Backlight
Message #7 Posted by Andrés C. Rodríguez (Argentina) on 4 Oct 2001, 5:33 p.m.,
in response to message #6 by Vieira, Luiz C. (Brazil)

Luiz: thank you for your comment! If you really like this kind of nostalgia for college days, you may read my article "Calculator memories from Argentina" in the memories forum, I hope you like it! (And... where in Brazil are you? We are close neighbours after all)

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