RF24 (Again!)
I’m still playing with my nRF24L01+’s, I’ve now got the RPi running the receiver as a daemon and the Arduino transmitter in low-power mode. The 3.3v 8MHz ATmega328p-pu now takes a reading (well at the moment its still a dumb counter!) and transmits it, then turns off the radio and goes to sleep for 30 seconds.
This is why its important that the Pi is constantly listening (well, sleeps every 5secs to reduce CPU load) and only overwrites the file if it receives a good reading.