Need a power supply and battery recharge circuit design

I have microcontroller board with me. which requires 5v as power supply. I want my board to run 24x7. I want a circuit which recharges the batteris and switch to battery supply without restarting the board.

My idea was to have 12v / 9v DC adapter connected to this battery circuit, where it will recharge the battery if required and 5v power will be given as output from circuit. this will be used to power the microcontroller board.

optional features in this circuit.
•Microcontroller can monitor the battery status by reading the a pin from the circuit / doing i2c / spi communication with circuit.
•Microcontroller can get an interrupt when power supply gets off and on. To know what is main power source

Ashok Kumar P

I see my batteries settling down to between 1.32 and 1.38 V after I have removed them from charging 24 hours previous. I would regard that as the volt level on a fully charged cell.

So if you leave the charger connected 24/7, then regulate its volt level to 1.35 V times the number of cells in your battery pack. Plus or minus a few hundredths of a volt.

If it is greater, then it will subject the cells to a few mA continual charge. A little is okay, but more will be bad for them, depending. You should investigate the safe limits for your batteries to make sure.

If it is less then the batteries may be slightly undercharged. This won't hurt them, but they will provide power for less time.

As for the supply's current capability, you must decide whether it needs to be sufficient to (a) power the device by itself, or (b) power the device AND charge a low battery pack.