battery power problem

I am working on home automation project.
In our project RF chip(microchip MRF24J40MB) is connected to the microcontroller atmel(atmega16).
RF chip is used to transmit the command from microcontroller via spi.
This whole unit is powered by battery.
If i press the switch of any bulb or fan the power ON the microcontroller and RF transmitter should transmit the command to the RF receiver placed on the receiver side.
Question is if i press the switch of any light or fan etc the MCU should be power ON otherwise MCU is OFF.
how i should design the circuit?
why i m worrying about this is i m using battery for powering, if battery is continuously ON the battery will last within an hour. How to solve this problem?
Which battery is better for this system?
NOTE : switch used here is capacitive touch switch .

Hi Ibrahim,

As there is no single answer to Your question I'd explain shortly just how I would do (and have done) it.

Firstly, implement your system as a state machine - that said, use standby (or any other low power) mode as the initial state for entire system. Then wake up MCU periodically (like after every 10 ms or so) to check weather during the _sleep_ time an event (button press) has happened. (Using capacitors for example as memory devices seems like an option)

If an event has been detected (cap charged for example), wake up other boards (RF namely) and process the information as You normally would and return to the initial state – sleep/standby (both the MCU and RF!). (Please refer to the AVR and RF manual for more details about power saving options)

Thus on this level of abstraction, it's rather a software not circuit design problem though some compromises have to be made on circuit design level as well.

I also suggest checking up nice work done here: http://jeelabs.org - pretty similar objectives anyway
There is a working example of a RF node working on a single 1.5 V (AA) alkaline batt for about one year.

Good Luck!

Hi Thomas,
Thanks for ur reply. we are currently working on your suggestions, but our main concern is
battery life and reliability.
Also can u please suggest a zcd that works on 230v Ac
Regards

Would the simplest method be to make the switches Double-Pole Double-Throw, so that each switch has contacts to switch on the system and simultaneously provide the input for the required light ?

That is, switch contact 1 turns on the microcontroller, and switch contact 2 provides a high on the microcontroller input pin that causes it to tramsmit the code for that particular light.

Or, to run from your capacitive switch, it could turn on both circuits by putting the signal through a relay or transistors (with a diode to prevent feedback).