A short update of my project.
With the help of @matthijs and @platenspeler, my node is now really power effient. I’m using an arduino pro mini 8mhz 3.3V (with led and regulator removed) + RFM95W + DHT22. To join the network I’m using OTAA. When the arduino is in sleep (with lowpower library) it uses around 0.02mA.
The problem now is that it takes really long to send the data. With this code the device wakes up for 20-30 secondes. It looks like the device is waiting for a TX window. Is it possible to remove this? I think it must be possible to send the data really quick.