PIC Microcontroller Note

Addicted to electronics, microcontroller, LED Dot Matrix, Led 7-Segment, PIC Digital Clock, Digital Watch, Led Dot Matrix Clock, Led Dot Matrix Watch, GPS and other DIY projects. Short notes about my PIC Microcontroller experiments sometimes it's just a short note sometimes it's a full PIC Microcontroller Project. The information here including source code and schematic are available for FREE, please contact me if you want the source files of the schematics/PCBs.

Friday, October 31, 2008

Battery backup for Microcontroller projects

My favorite PIC Microcontroller projects are clock projects. All of my clocks are powered by 5V DC wall wart adaptors. In case of power failure, the clocks stop and I have to set time when the electric power is restored. This problem will not happen with the clocks using DS1307 RTC as it provides battery backup capability. However, the clocks without DS1307 or any other RTCs will suffer from power failure. The circuit below is an example of the use of battery backup circuit with PIC16F627A or PIC16F628. The circuit can be used with other Microcontroller chips as a battery backup source. It also provide power failure signal (active low) for further processing.

-- Updated 21 Jan 2009 ---
The 1N4148 diodes should be replaced with Shottky diodes, such as, 1N5819 or 1N5822 for lower voltage drops at the diodes.