Hi all,
Things went quite well so far :). It is a national holiday, everything closed and the weather is rather sad. Perfect for tinkering with Arduino and RPI 
I managed to get nanopb (protobuffers) working on both Arduino and RPI, and they can happily exchange data. The Arduino will sent sensor info from a DHT11. The RPI will sent some random values as test. The Arduino does stuff with the interrupt pin of the nRF24L01. I plan on writing a bit about my experiences later on, to help others getting started.
Now, there is only one issue: power consumption. I have been testing a bit, and using the RocketScream library I can get to 27 ma with everything attached. Removing the radio makes it go down to 12 ma. And then there is this big gap between 12 and 0.06 all caused by the linear voltage regulator I use (http://www.ebay.co.uk/itm/1PC-New-DC-DC-4-5V-7V-to-3-3V-AMS1117-3-3V-Power-Supply-Module-Voltage-Regulator-/301123756227?ssPageName=ADME:L:OC:NL:3160). I checked the datasheet of the chip used (AMS1117) and it is about correct.
Now I was thinking.. What if I put the entire circuit of the regulator behind a transistor and occasionally turn it on when transmitting data? That should work right?
Or did anyone else have solutions to reduce the power consumption. I would like to power the device with some batteries, so 27ma is quite much :). I could not find so much information regarding the nRF24L01 and this.
Thanks again for any suggestion
Edit: Oops, overlooked tasosstr's reply. I will look at that voltage regulator and see how much mA it consumes