battery power

How to power the RF transmitter while i have to transmit any command?
After transmit power should be OFF.
Next time when i have to send command power should be ON, Otherwise OFF.
power is given by the battery.
Note : RF chip is connected to the Microcontroller and data is send via SPI?
can anyone help me?

Well, a simple MOSFET switch will work, simply add the MOSFET in series with the device and control the gate voltage with an I/O pin on your microcontroller. You'll need to make sure to use a MOSFET which will handle your current draw from the transmitter.

Hope this helps,
Tim

Can you give us some more detail? What RF chip are you using?

You may be able to control an Enable line on the chip if one is available, i.e. set enable line, send command, clear enable line.

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 .

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 .

Or, the microcontroller output might be able to power the transmitter directly. Example: The Linx LR series transmitters run on 3 volts and draw on the order of 4.3ma when transmitting at the 6dBm level. Most PIC microcontrollers can source 20ma. So, you could actually power the transmitter with a PIC ucontroller output. OR, if your transmitter chip has something like the Power Down (PDN) feature that a Linx LR transmitter does, then use that to turn the transmitter on and off (or more accurately, take it out of, and put it into a low current drain stand by mode).

Just make sure to match the power requirements of the transmitter device.

how to power microcontroller using battery while i m pressing any switch of appliance.
If i release the switch the microcontroller power should be OFF.
Which battery is better for this project?
NOTE : switch used is capacitive touch switch.

Not sure if I know what you're asking, but I'll assume it's about that chicken/egg problem of if the microcontroller is off, then how can it be turned on my a capacitive touch switch:

I don't know the atmel microcontrollers (I use PICs), but if the atmel has a low power sleep mode, then have it go to sleep, then periodically wake to poll the touch switch (like every 50ms or so). The microcontroller is never really 'off', but instead is asleep (except when it's polling the switch, which shouldn't take much power, esp, if the clock speed can be kept low. On a PIC i would use the watchdog timer to periodically wake the microcontroller.

But, this will only work if the microcontroller has a sleep mode with a low enough current.