Hello Mauricio,

You *may* find out it will cost more not to use a specialized RTC chip, but
it is worth investigating alternatives (time is money too). You may have to
spend more money on a heftier lithium to compensate for the larger current
draw of a non-RTC solution (such as a PIC -- unless the nanoWatt devices fit
the bill).

Also if you have not already implemented the following on your PCB, please
do...

Two side note caveats regarding your lithium battery:

1) It is always a good idea to place a current-limiting resistor (~470 ohm)
in series with the positive lead on the lithium battery (as close to the
lithium battery as possible). You don't anyone accidentally shorting out the
battery during PCB troubleshooting/testing and having a lot of current
dumping through a PCB trace. Not a pretty sight.

2) Be careful and choose a diode with *low* reverse leakage characteristics
when protecting your lithium battery from being charged when standard Vcc is
applied to the PCB -- that is unless the RTC clock itself takes care of this
through a Vbat input.


Just some food for thought. Good luck in your quest.

Best regards,

Ken Pergola



-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Mauricio Jancic
Sent: Friday, July 11, 2003 5:50 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: [PIC] PIC as an RTC, is it recomended?


Hi!
    Hello again all!! I need to make a system that must have a Real Time
Clock. I just don't want to add 2~3 dolars to my product by adding the
DS1307, wich is very good, but also expensive here in Argentina. So, I'm
considering on using a PIC16F628 to perform the requiered tasks and,
also, mantain the actual time. So I would like to know you  opinions on
this, I I will use a standard CR2032 3V battery to mantein the time when
no power is pressent. Do you think that this could work? For how long if
I only try to mantain the time ?


    Thanks!

Mauricio Jancic
Janso Desarrollos
(54) 11 4542 3519
Republica Argentina
Microchip Consultant Program Member


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