Jimster:
Hello, I plan to use the manicabug RF24 library to monitor 4 remote sensors from a central arduino with LCD display. What I would like to do is send data from the central arduino back to the sensors to shut them down when required. I’d then turn the sensors back on manually when needed (locally on each one). What do you think is the best way of doing this, as at the moment if I understand it correctly the communications is not bi-directional?
Would I have to have change the role of the sensor from transmitter to receiver after every few seconds to check if off signal was being sent from the central arduino, or is there a more elegant solution?
It seems you have much the same intention as me, but I'm not sure that is really what you want.
I'm not aware of any sensor that can be shut down, powered up, or changed from transmitter to receiver. You do this with Arduinos to which the sensors are connected. In your case I guess this is four Arduinos, each with one sensor connected, and each connected to an RF24. IOW, a network of five Arduinos, using RF24s.
The RF24 is a transceiver. An example in the standard library shows how it is turned transmit/receive. I think you need to do that in order to ensure synchronisation, but it appears quite straightforward. There is information around about establishing a multi-station network.
http://maniacbug.github.com/RF24Network/index.html
I don't see why you need to shut anything down, unless you have serious power supply problems. I certainly don't see why you need to do anything manually. A lot of this stuff has extremely low power demand when it is not active. I had never seen an nA until I came to this world.
If power is an issue, you might find the smaller Arduinos useful, like the teensy or w.h.y. for the remote stations. They may suffice, as your code requirements are not that great.
On another tack, I believe Xbees can be used as a wireless arm to a sensor, i.e. no Arduinos involved in the remote operation, only at the base.