Example Sensor Node Firmware with a BMP/E280 or SHT21 Sensor. Used Sensor has to be set via #define in the src/secconfig.h (HAS_BME280 or HAS_SHT21). Please change the values in src/secconfig.h to your Keys from https://console.thethingsnetwork.org. Device has to be set to ABP Mode. Also since there is no permanent storage to store the Frame Counter, please disable the Frame Counter Check in the TTN console.