>
>         I'd like to thanks all that replyed to my question.
>         In this circuit I'll use the method described by Mike Smith
> to store "battery used time" since I'm using nicad.
>         Using one or two EEPROM locations I can create a counter that
> increment every minute and, when a determined count (time) is reached
> I can display a message with a safety margin to recycle the battery.
>         When the battery is recharged I can press a button before turn-on
> the device then, at power-up the start routine check the button and if
> pressed reset the counter.
>         Another thing that flashed my mind is to use the EEPROM counter as a
> safety device so, when a preset used time (or number of power-up's)is
> reached the user at the next power-up MUST press a pre-determined sequence
> in the buttons, otherwise the device becomes useless.
>         To increment the counter on EEPROM every minute is no problem since
> 1x10^6 cycles (EEPROM safety margin)  = 694 days, 24 hours a day and, the
> circuit is used 2 or 3 times a day (one hour max.).
>         Note, this is note a comercial device.
>         Now, another question ...
>
>         Do nicads self-discharge when not in use ?
>                 If yes Then
>                         this method becomes half useless
>                 End If
>         Loop
>
> Thanks again.
>
> Ricardo Seixas

>
>      Ahhhh!
>
>      I am also trying to define a way of implementing a 'low battery'
>      detector.
>
>      I have set up a GPIB system to make LOTS of measurements on a battery
>      discharging, and it is becoming clear that just measuring an absoulte
>      voltage to determine that the battery is about to fail is pretty bad.
>      The behaviour of one battery pack to the next means that if using a
>      voltage threshold as the decision for sensing the battery low
>      condition that I will get from 1.5 minutes to 10minutes difference.
>
>      I have come to the conclusion that meauring the rate of change of
>      voltage drop is a MUCH better way. And is this what you are saying?
>      Measure the voltage every 10 or 20 seconds or so and look at the
>      difference between samples. This way you are going to 'quite' reliably
>      going to find the 'knee' in the discharge curve of the battery just
>      before it starts plumeting and your supply voltage becomes
>      unregulated.
>
>      regards,
>      SW.

>
>
>        I'd like to thanks all that replyed to my question.
>        In this circuit I'll use the method described by Mike Smith
>to store "battery used time" since I'm using nicad.
>        Using one or two EEPROM locations I can create a counter that
>increment every minute and, when a determined count (time) is reached
>I can display a message with a safety margin to recycle the battery.
>        When the battery is recharged I can press a button before turn-on
>the device then, at power-up the start routine check the button and if
>pressed reset the counter.
>        Another thing that flashed my mind is to use the EEPROM counter as
a
>safety device so, when a preset used time (or number of power-up's)is
>reached the user at the next power-up MUST press a pre-determined sequence
>in the buttons, otherwise the device becomes useless.
>        To increment the counter on EEPROM every minute is no problem since
>1x10^6 cycles (EEPROM safety margin)  = 694 days, 24 hours a day and, the
>circuit is used 2 or 3 times a day (one hour max.).
>        Note, this is note a comercial device.
>        Now, another question ...
>
>        Do nicads self-discharge when not in use ?
>                If yes Then
>                        this method becomes half useless
>                End If
>        Loop
>

>On Tue, 14 Oct 1997 17:58:00 -0300 Ricardo Seixas
><RemoveMErseixasTakeThisOuTCICLONE.COM.BR> writes:
>>
>>        I'd like to thanks all that replyed to my question.
>>        In this circuit I'll use the method described by Mike Smith
>>to store "battery used time" since I'm using nicad.
>
>I believe in the original post you said the project was a portable
>measuring device.  What does your device do as the battery runs down?
>Does it (a) just quit all of a sudden, or (b) give inaccurate readings
>when the battery voltage is low?  The latter condition is very bad.
>Others have proposed schemes to give an early warning that the battery is
>failing.  This is somewhat difficult on NiCds and may not be of much use
>anyway.  Users will correctly deduce that a mode (a) condition is a dead
>battery.  But you need the circuit designed to guarantee that
>mis-operation in mode (b) will not happen.  Regardless of the battery
>type, this is done with a simple absolute voltage detector or design of
>the circuit so it always goes to mode (a) first.

>
>>        Using one or two EEPROM locations I can create a counter that
>>increment every minute and, when a determined count (time) is reached
>>I can display a message with a safety margin to recycle the battery.
>>        When the battery is recharged I can press a button before
>>turn-on
>>the device then, at power-up the start routine check the button and if
>>pressed reset the counter.
>
>This assumes that the battery will be fully recharged every time.  The
>time needs to be decreased as the battery loses capacity due to age, or
>you could set it rather short from the outset so significant capacity
>will be sure to remain.  This will lead users to ignore the warning
>though.
>
>Users often only charge enough to get a little more use.  This is rough
>on the battery, but what do they know?  Also they may have to if they
>can't afford the time to take the device out of service for a full
>recharge.  They may ignore the warning and continue using until the
>battery is dead.  That's why it needs to be designed to stop gracefully
>when the battery expires.