Battery backup system

[togarha]

Hi!

I'm making a system with main power and a 3V battery (some like CR2032) through a diode for RTC keeping time. Then I want to monitor the charge of battery to light a led when the battery is close to the end of its life to inform the need of change it. How can I monitor the charge? I have a PIC microcontroller (with AD peripheral, comparator, etc) in the system.

Thanks in advance...

Regards,

 

[BobK]

Hello,

Microchip.com has many manuals and application guides available on their website. In their "Tips N Tricks" manual the first Tip is Low Battery Detection. They also have a "Comparator Tips N Tricks" manual. Melanie Newman posted on PIClist.com several years ago "Comparators 101" which uses low battery detection as the example.

I don't think you can charge a CR2032. I use them on my DS1337's but I write a "service required" routine into all of my clock-based programs so the customer must have their system looked at every 2 years. I'm in the service revenue business. I also update the DST files at that time and offer program updates.

Hope this helps you!

BobK

 

[IanP]

Lithium battery holds its voltage till it's almost dead, so you can set the critical voltage to 0.8 (80%) of its nominal voltage, roughly 2.5V .. see chart below ..
To ensure its long term operation make sure you don't drain it to much while reading its voltage - use high impedance buffer between battery and PIC's ADC pin and a MOSFET switch to disconnect battery from the sensing circuit ..

Regards,
IanP

 

[togarha]

And for R6 non-rechargable bateries??