battery related problem

[iknaitey]

I am working on home automation system 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 should be provide to the microcontroller and RF transmitter, 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?
NOTE : switch used here is capacitive touch switch .

 

[godfreyl]

Can't you have the microcontroller permanently powered, and use that to switch the RF chip on and off as appropriate?

 

[chuckey]

The crude way would be to use a transistor as a series switch to the micros +Vcc line. It might be that the micro will take too long to reboot, meaning that you will need proper latches to hold the state of the switch until the micro wakes up scans the latches then resets them (if applicable). I would tend to find out what is actually taking the power (should be the transmitter module) and just switch that off. One technique for the micro could be to slow the clock down during its waiting phase.
Frank

 

[iknaitey]

Can't you have the microcontroller permanently powered, and use that to switch the RF chip on and off as appropriate?

The power is provided using battery. If i powered microcontroller permanently, the battery will last within few hour.
Please tell me how i should design this circuit?
Which 9vbattery is long life for this circuit?

 

[godfreyl]

The current drawn by the microprocessor should be small, so a normal 9V battery should last a long time. The radio transmitter uses much more power so it should be switched off when it's not needed to save battery life.

If you look at the datasheet for the microcontroller, you can find out how much current it uses. Then, if you look up the capacity of the battery, you can work out how long the battery will last.