The Digispark is a Atmel Attiny85 based microcontroller development board similar to the Arduino line but cheaper and smaller. They had an extremely successful Kickstarter campaign 2 years ago and clones are available on ebay a few euros.
They seem to now have their own ecosystem and can emulate a USB device. The USB is also used to programme the microcontroller, the same way it is done on Arduino.
For reference, here is the schematic of digispark.
Here I need only two pins for the project : 1 for the RF receiver and the other one for the serial connection to to Raspberry Pi.
I decided to go serial instead of I²C mainly because of the asynchronous nature of the signal and to avoid polling from the I²C master (Raspberry Pi in my case). Here the digispark will simply send its data as soon as it decodes something from the RF receiver.
So PIN 0 will be the RF receiver IN while PIN 2 (default for Serial Debug) will be used for the Serial Communication. 38400 bit/s seems to be the recommended value. Fair enough.
Code is available on github :https://github.com/guillier/la_crosse_sensors
In order to allow serial communication, the serial port has to be freed from any usage as a console. Once it is done (and the Raspberry rebooted), minicom can be used to check if everything is alright.
minicom -b 38400 -o -D /dev/ttyAMA0
Note that the port is
/dev/ttyAMA0 while the one for the Z-Wave static controller is
Same as the values from the airpi sensors, these ones can be stored in RRD databases:
rrdtool create temperature_device33.rrd --step 300 \ DS:temperature:GAUGE:600:0:U \ RRA:AVERAGE:0.9:1:24 \ RRA:AVERAGE:0.9:6:35064 \ RRA:MIN:0.9:288:1826 \ RRA:AVERAGE:0.9:288:1826 \ RRA:MAX:0.9:288:1826