Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!cs.utexas.edu!rutgers!orstcs!guille!daver
From: daver@guille.ece.orst.edu (Dave Rabinowitz)
Newsgroups: comp.sys.handhelds
Subject: Re: Want HP-28S fuel gauge, program name query
Message-ID: <14570@orstcs.CS.ORST.EDU>
Date: 29 Dec 89 19:54:59 GMT
References: <4374@rtech.rtech.com>
Sender: usenet@orstcs.CS.ORST.EDU
Reply-To: daver@guille.ECE.ORST.EDU (Dave Rabinowitz)
Organization: Oregon State University, E&CE, Corvallis
Lines: 21

In article <4374@rtech.rtech.com> glenk@llama.UUCP (Glen Kilpatrick) writes:
>*  What about a "fuel gauge" for the 28?  I'd like a function that
>would return a real number between 0 & 1 indicating battery voltage,
>where 1 = new batteries, & 0 means the low-battery indicator was
>just triggered.  If it could report hours of continuous computation
>left, it would be a googol times GREATER (but that's too much to
>hope for!)!

The hardware in the 28S uses a simple comparator to compare the battery voltage
to an internally-generated reference value, so it cannot arbitrarily measure 
battery voltage.  There are two such comparators in the calculator.  The first 
tells the software to turn on the low battery indicator and the second, at a 
lower voltage, tells the software to shut down the calculator completely to 
avoid the chance of some incorrect operation messing up memory.

The calculator speed was set to assure correct operation down to this lowest 
battery voltage; processor speed varies with battery voltage and if the voltage
gets too low some logic might not reach the correct state before its output is
sampled.  If the calculator has been sped up using one of the programs which
have been posted here it is possible that memory will be messed up or lost as
the battery voltage drops with age.