Algorithm 1. Pseudo code of the Firmware at the sensor node operated in the measurement mode

1: Call the required libraries (waspXBee and waspSensorPro),

2: Initialize and power on each sensor,

3: Read serial numbers (stored in the EEPROM of each sensor) of sensors used in the node,

4: Wait 90 s for sensors to warm up,

5: Acquire 5 readings from each sensor and compute their average,

6: Apply the calibration/correction formulas (one for each sensor identified by its serial number) for the sensor reading,

7: Save the timestamped-measured data in SD card,

8: Send the data via XBee interface to the gateway,

9: Switch the sensors and radio module to sleep mode for 13 min,

10: Wake up the sensors and radio module,

11: Go to line 4