From: kolstad@cae.wisc.edu (Joel Kolstad)
Subject: Re: HP48 batteries bug?
Organization: U of Wisconsin-Madison College of Engineering
Date: 26 Dec 92 20:39:53 CST

In article <Bzw0ys.GEo@news.iastate.edu> twh18@isuvax.iastate.edu writes:
>Oops!  Bateries
>are low?!  I tried to put the intensity of the display darker by
>press <On> and + together.  The screen became dark enough that I
>no longer can see the menu.  Now, that's ridiclous.  If it has enough
>power to turn the intensity so dark, how could it be low on batteries.

The 48 has a well regulated power supply that'll most certainly keep the
LCD voltages (which directly affect the constrast) up to their nominal
levels even after your 48 will turn off immediately after being turned on.
(The 48 has two battery level indicators; the first is the one you see.
The second one [which is set lower than the first] causes the OS to turn
the 48 off immediately.)

>On my TI-85, it has like 10 levels of intensity, and each
>intensity can be separated by another 3 sublevels of intensity, together
>that's 30 levels of intensity.  When I had to turn the intensity on
>my TI-85 to the highest intensity setting and the screen is still dim,
>I know I need replace batteries on TI.

Yeech!

>	Another thing is that on my TI-85, it has a Cell backup battery,
>which is used to maintain the memory while the calculator is turned off/or
>during the main batteries changing process.  However, I didn't catch this
>on my HP48.  The HP's instruction book
> neverd mentioned anything about the secondary
>battery nor it said about replace it other than replace the main
>3 AAA(this sounds may like triple A - Anti-Aircraft-Artrilly, but it's not:)
>batteries.  The only thing that the book said is that replace the batteries
>in 2 min to avoid memory loss.  So, does anyone know what keeps the memory
>while the HP48's batteries are being changed?  If there's a secondary
>battery inside, when and how are we going to replace it?

There's a capacitor instead.  If you take out the batteries and press "ON",
you'll kill your memory. :-)  The two minute warning in the manual is
actually quite conservative (as it should be); people have reported having
batteries out a lot longer than that and not having the 48 go brain dead.

>	In addition, does keep a lots of programs on the HP uses considerable
>more power? (say you have like 20K in RAM, would it uses much more power
>than usual?)

Nah.  If you have plug in expansion cards, those (of course) suck a little
extra power.  

When you're staring at the stack display, your 48 is in what's called
"light sleep" mode: The CPU is off, but the display controller is on.
Pressing any key (as well as alarms, etc.) "wakes up" the CPU.

Games such as Tetris keep the CPU on all the time, which uses considerably
more power than just using the machine for adding numbers.

>	Last thing (yeah, finally:), would it be a good idea to leave the
>HP48 on or just turn it off if you know you are going to use it in 5-8 minutes?
>This may sound stupid, but I just love my HP48 so much that I don't want the
>On key to "die first" while other keys still functional:)

Actually, I'd be more concerned about the "Enter" key. :-)

For 5-8 minutes, I think you might as well leave your 48 on.  (Especially
because the turn on/off delay gets annoying if you have a lot of RAM in
your 48.)  The OS will do the auto-shutoff thing in about 10 minutes, I
think.

>	Man, wouldn't it be great if the HP48 had a backslide case on like
>the ones on TI-81/85?

Hmm... not a bad idea.  Too bad the grooves on the 48 are nowhere near the
middle of the casing.

						---Joel Kolstad