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PICList Thread
'[PIC]: Battery monitoring'
2004\01\05@123812 by Edward Cooper

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Hi All

Perhaps you can help me out on this.  I want to produce a system for
monitoring the voltage of my device's batteries which can then be used
in charging and discharging.

I'm thinking about using the reference of my 5v voltage regulator is
the base, and then looking at the battery voltage on top of that.  The
batteries should never go above 10v so I shouldn't then need to do any
sort of dividing and it should be quite accurate.

However I'm not sure whether this is a good idea or how to do it?  I
must connect the 5V line up to one of the pins on the PIC but I'm not
totally 100% confident which one, also I need to read in a A2D reading
for the current and I think this will be impossible if I'm referencing
from 5v as my shunt will need to be referenced from 0v....

Any ideas how I go about this?  Also is a good idea to stick some
zeners on the pins of the PIC just in case the value ever somehow got
over 5v?

Cheers

Ed

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2004\01\05@130050 by Lucas Hartmann

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face
part 1 1736 bytes content-type:Text/Plain; (decoded quoted-printable)

Hey! Watch out!



Analog input pins sholudn't be driven above VDD or below VSS at any
situations.



Connecting the 10V line to any analog input will get the input, and maybe
the whole PIC, damaged.



The voltage divider is, however a good idea.



Lucas Hartmann



--{Original Message removed}
part 2 531 bytes content-type:image/gif; (decode)

2004\01\05@131721 by Edward Cooper

picon face
I was under the understanding you could use nearly any voltage as a
reference for the PICs A2D and then measure readings relative to that?
Perhaps not

Ok then next plan

BattV --------######---------######-- a PIC pin here (ie B0)
                                   |
                                   |
                               A A2D Pin here

Switch B0 low, and measure the voltage on the divider?  Is this a good
idea, what happens when I power the whole thing off, will current leak
through the A2D pin?  Should I use a zener diode somewhere for safety.

Cheers

On 5 Jan 2004, at 18:00, Lucas Hartmann wrote:

{Quote hidden}

> --{Original Message removed}

2004\01\05@134805 by Wouter van Ooijen

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> I was under the understanding you could use nearly any voltage as a
> reference for the PICs A2D and then measure readings relative to that?

yes, provided that it is in the gnd .. Vcc range, and there are some
more restrictions if you want the full accuracy of the A/D. The
datasheet is your friend.

Wouter van Ooijen

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2004\01\05@143056 by Olin Lathrop

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Edward Cooper wrote:
> I was under the understanding you could use nearly any voltage as a
> reference for the PICs A2D and then measure readings relative to that?
> Perhaps not

Perhaps you should read the data sheet.  The absolute maximum ratings are
there for a reason.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2004\01\05@143717 by Edward Cooper

picon face
> Edward Cooper wrote:
>> I was under the understanding you could use nearly any voltage as a
>> reference for the PICs A2D and then measure readings relative to that?
>> Perhaps not
>
> Perhaps you should read the data sheet.  The absolute maximum ratings
> are
> there for a reason.

Will do, don't want any popping PICs :)
Anyway I've gone off the method of measuring the offset from the
regulates supply, and I think I'll just go with the potential division
method.

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2004\01\06@115310 by DOC

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There's an article in the November 03 issue of Servo Magazine
called "Battery Fuel Gauge" written by Fernando Garcia.

Might help. Uses an AD7755 and a PIC 16F84 !?

Code at:
http://www.servomagazine.com

DOC

http://www.robot-one.ca


At 05:35 PM 1/5/2004 +0000, you wrote:
>Hi All
>
>Perhaps you can help me out on this.  I want to produce a system for
>monitoring the voltage of my device's batteries which can then be used
>in charging and discharging.

...

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