HP Forums

Full Version: Viewpoint about RED LED calcs and batteries ...
You're currently viewing a stripped down version of our content. View the full version with proper formatting.

Here comes a grand idea... and an opportunity for debate :o)

In the past, some debate has been had, about whether RED LED calculators are worth the hassle of keeping them charged up.
Also, whether RED LED's are better (bright-sunlight users say 'no', office-cubicle people say 'yes').

But the big thing is, RED LED's draw more power, and the charger had to be used to frequently top-off the NiCad batteries. Some would say that's a reason to call them impractical, or inferior to LCD, or say 'you can't get away from a 120V wall socket'.

BUT....... it just depends on your batteries. In the context of spice-model calculators (HP-34C) I would suggest that somebody who acquires one should just stuff in "AA" Alkaline batteries, and set the plug-in charger aside. That's what I did with my 34C I acquired.... and I haven't had to mess with any batteries since.

I'm saying, dont bother charging them, its a hassle. Just plug-in non-rechargeables, and replace them once in a blue moon when they need replacement (wont be that often).

Now then, to the idea of the day...... why not just stuff in AA PHOTO-LITHIUM batteries ?!? When my AA Alkalines finally quit, someday, maybe a year from now, I'd tend towards the AA Photo-Lithium. Sure, we're talking about some ungodly sum of money, maybe $8 a pair, BUT, then you're done, man. Its like an Atomic Submarine..... it will just keep going and going 'cuz the nuclear reactor wont quit.

And if this takes care of power concerns with the RED LED's, so you can just kick back and enjoy the ride, well, isn't the price of AA Lithium batteries worth the peace-of-mind.
I don't use my 34C all that often. I still do the majority of calculating on my fleet of 'throwaway' HP-32S. The cats walk on them, and they get house dust ground into them, etc.
I bring out the 34C kind of like bringing out a bottle of fine wine.... finest aged RED wine. At that rate of usage, a set of Photo-Lithiums will probably last 4 to 8 years. So why are we all so frightful about the power consumption issues of classy Red LED calculators ??
(none finer than HP-34C).

- Norm

Dr. Michael Meyers (no relation to the movie star)(or the movie character) has been advocating the 1.5V lithium batteries for a while here in the Forum. You can find several threads on the subject in the Archives.

Norm:

If you like LEDs so much, go for it, man. Knock yourself out. Me, I truly don't care for LEDs because (to my eyes) the slightest moonbeam is enough to diminish their effectiveness, and I do need light to see what buttons I'm pressing. That is the _only_ reason I advocate in favor of LCDs. Other than that, the choice is irrelevant except for matters of taste.

I have an alarm clock with gigantic LED numbers. At first I had no problem using it, day or night. After several years of continuous operation, however, I can hardly see the stupid thing by day. Could this mean that LEDs wear out, becoming dimmer and dimmer?

-Ernie

One problem with using regular size AA cells is that they are a little longer than the flat-top NiCads that HP used. I think a lot of people have tried them at one time or another, I did in my 25 which is tied for first of my LED HPs (I got a 45 and a 25 at the same time on Ebay from Gene, and learned about the HP Museum at the same time!) In the Woodstocks, the springs are long enough that the extra length of the cell isn't too much of a problem (those springs are already mighty strong!) but in the Spices I think it has caused a lot of broken battery contacts.

Ernie wrote:

> and I do need light to see what buttons I'm pressing. That is the _only_ reason I advocate in favor of LCDs.

I second him in these words and I'll post a few of mine again.

I like Continuous Memory and amongst HP LED-based continuous memory calculators, the best one for me is the HP34C. Well, I think it's the LED-display with the best set of features, right? I'm not counting the off-road HP95C, of course.

I don't like the idea of having to recharge batteries for ten to twelve hours so I'll be able to use the calculator for three to four hours. I know, you are talking about disposable cells; I prefer rechargeable.

I use graphics and I prefer having custom ALPHA strings to help signaling conditions. HP LED-display calculators neither have ALPHA capabilities, nor graphics. At least so far.

After reading about Organic LED's and their amazing characteristics, I believe a hybrid display OLED/LCD is the final frontier: lights for those who need enlightment, shadows for those leaving the darkness... Wow!

Luiz C. Vieira - Brazil

Have you been to the optometrist lately??

>Have you been to the optometrist lately??

Yes, thank you. It's that my age (pushing 48 now) and the AIDS virus have reduced my ability to discern small images and patterns. Nothing that can be fixed, alas...

-Ernie

Is LCD with green backlight a good compromise? I mean, you can have a good seeing in a dim environnement and no backlight need in sunlight and you can get all ALPHA and graphic you need AND i think it consumes less power to backlight than to use LED

But i understant, i really LOVE LED calculators is fun and charmy to use in the lazyboy but for "real" business, i prefer the 41c or a 48G...

I agree with Luiz whe he said continuous memory is important and LED don't show this too often (Hp-25C, TI-58C). I will add that i also like when a calculator can hold more than a program at a time and i don't know any led that can do that without doing a bid program cut in independant one; aother advantage of the 41!

ellis; hp sold the battery packs with a little spacer held on by two sided tape at the bridged end. it has the springy prongy thingers of the stainless steel wrap around there too. if you just use a piece of aluminum foil as the bridge then regular AA cells are no (or not very much) tighter than the rechargeable pack.

btw: i finally got that resistor. thanks for the instructions and the hand holding.

To answer the question about the LED alarm clock:

LEDs DO diminish over time; they eventually get less and less bright. LED manufacturers do measure a useful life to half-brightness. This happens, in your standard GaAs red LEDs, well after one-hundred thousand or more hours of operation.

Organics are much less long-lived... so far. This is one of the things being worked on.

I dunno how long ago you bought your clock. I imagine though, that it has been on all the time since it became your clock. It should have a useful display life MUCH longer than the hours of operation alone might imply, simply because not all segments are on all the time. I would figure a LED clock should go about 35-40 years before it dims to half-bright, and even then, some segments will fare better than others.

Overvoltage and a punishing duty-cycle when multiplexing might prematurely age LED displays. Conversely, you may NOT be seeing the aging of the LEDs at all-- what you MAY be seeing is the aging of the driver circuit. Remember, LEDs can look a lot less bright if the voltage supplying them drops just a small bit. A failing capacitor, say, in the supply circuit might cause you to think the display was getting weak...

ah, so that's how my ham-fisted brother broke the contacts on my 32e. he denies it tho'

im with norm on this. in fact, ive been looking for a simple calculator that emits light (doesnt have to be LED specifically) could be backlit even. using recharge AAA cells thats 1500mAh for a pair which should last some (dry cells are a lot more).

something ive noticed now is that dry cells dont last anymore. i mean last when not being used. is it because they are all manganese dioxide rather than good 'ol zinc carbon? packets have sell by dates that are only a year or two away. duracell claim their quoted shelf life is when its down to 80%. i have some old fashioned zinc carbon batteries in LCD calculators from the 80's that are still going strong. about this time manufactures noticed that they were nuts to put two AA batteries into LCD units and it all switched to button cells.

if you're wondering why i need an led unit, its so i can figure the bill in dark restaurants. in fact, im considering the idea of carrying a pocket slide rule for this. then i wont need the batteries at all :-)

Long ago, my math instructor gave this short-but-sweet comparison of my slide rule vis-a-vis his HP-21: "Less than half the precision, doesn't need batteries, but does require an external light source." (Or something like that, anyway.)

I've been meaning to ask about your battery charger! I'm glad to hear it's progressing.

I never had a real Spice battery. I've used foil to make the connection and then some neat woven copper tape - that worked but began to corrode a little after a while. Currently I'm using flat top NiCads with an official welded strap to make the connection. I got a 4 cell pack and cut it in two, I use half in my 34C and the other half in my 25 - I filed off every trace of the straps on the new working contacts.

Someone here has mentioned 3 mil nickel tape (with adhesive?), I'd like to try that. I'm always trying to think of uses for the little strips that are inside the "security devices" that are stuck on everything sold nowadays, they look like they would be useful for something. They are very thin and metallic looking. I've never actually taken an ohmmeter to them but they look like metal. They are so thin that they would be good to make the connection in the Spice battery compartment, if they are conductive.

It is important that such a piece of metal be as thin
as possible, so that the "AA" batteries can be jammed
into there.

a metal with an adhesive backing sounds clever.

Dont do this, but aluminum-foil ducting tape comes
to mind. That adhesive never comes off. But dont do
it because aluminum doesn't have resistance to oxidation.
The result will be poor.


However, it is nice to be able to replace the
home-brew strip of metal that you choose. Therefore
I would just grab something and stick it in there, and
replace it later with something else.

Very thin nickel-metal-foil should be the ultimate.
Copper foil might also be suitable. A bit of an
old 'flex' circuit might also suffice.

I dont have any. I just use a bit of copper
"solder-wick" such as the technicians use to remove solder.
The flux that is mixed into it seems to do pretty well at
maintaing gas-tightness, no oxidation, and 100% conductivity of the metal material.