I went to Lamington road ( electronic market)
got my hands on ds1302 ( non I2C) it is cheaper than I2C costed Rs.75
bought a lithium battery and a battery carriage
and also the 32.786Khz crystal

I am thinking of giving power supply via a ups ( I can get it for around Rs.2000 a 600 VA , but I will go for 500 VA),else I need to make my own battery backup system..

There are two ways I am thinking of solving the sensing problem
1. try to use the ups signal ,from serial cable of ups
2. andy's method port pin <>Opto coupler <> +5V

Any could you give me a refrence design in connecting opto couplers like MCT2E,last time I tried nothing happened.



Ragu can you tell me is it good to use a smps power supply ? I have heard many small devices come with smps power supply they give better effeciency, are they available in open market for 5 V supply

Thank you
Deepak