http://www.8051projects.net/ Learn to make simple microcontroller projects, pic, 8051, avr and arm projects. download 8051 projects, tutorials, libraries, sample codes. join the microcontroller discussion forum and ask doubts regarding electronics. the best source for 8051 over internet. en-gb 2009-01-08T08:36:15-08:00 contact@nospam.com hourly 1 2000-01-01T12:00+00:00 http://www.8051projects.net/forum-t13335.html 2009-01-08T08:36:15-08:00 Ajay, i want to add a backup battery(or some other convenient source) just to run the RTC for infinite period of time, what modifications will be necessary in the schematic and C code http://www.8051projects.net/forum-t13335.html 2009-01-08T08:36:15-08:00 Arun Kumar V a battery and a diode !Arun http://www.8051projects.net/forum-t13335.html 2009-01-08T08:36:15-08:00 pdi33 there are a couple of doubts for ur requirement before we proceed:1. do u want the whole system operable (including keys/display ) on battery or only the internal RTC clock?2. What is the type of battery u plan to use?rechargeable like Ni-Mh /Ni-Cd or Dry cell like Zn-Cl/Alkaline?If u want to run the whole system , these are suggestions to reduce power consumption of the circuit:1. change the hardware using the diode/cell as suggested by arun and take care that the backlite LED is only run by mains source ( it is the only part which takes a lot of current).2. try reducing the crystal frequency of the uC and change the time period appropriately in the code. the power consumption of the uC in directly proportional to the frequency of operation. Use a optmum crystal frequency to suit the application.3. isolate the alarm output ciruitry to operate only on the mains power source ( a buzzer too takes a lot of current )4. Increase the pullup resistor values of the peripheral circuitry to the maximum possible value.Note that though some external components consume only a few mA of current , a difference of a few mA matters a lot while running a battery operated circuit if u want the battery to run the circuit for a longer time.Alternately, if u want the uC to operate like a RTC chip ( equivalent to a DS1307/Ds1302), u may have to make major modifications in the peripherals of the uC. the 89C51 does not support tri-states for its port so the current consumption of the uC alone depends upon the peripherals connected even if they are not given supply from the battery. So ideally, u may have to connect the peripherals through a buffer which supports tri-states. http://www.8051projects.net/forum-t13335.html 2009-01-08T08:36:15-08:00 Nisarg I am also having the same doubt! I want to use Dry cell for backing up only microcontroller. How can I connect that, please help me with some circuit description. http://www.8051projects.net/forum-t13335.html 2009-01-08T08:36:15-08:00 pdi33 well, if u need to reain supply to only the uC, then u will need two diodes for the job Vcc ----> diode -->| ______________ | ---> uCVbat ---> diode -> |If u reall want to make it efficient, then there would be some more modifications neccesary to sense the mains power down by the uC to put it in idle mode, differentiate between a cold reset and warm reset while waking up the uC on power on, etc...