After the mixed experience with the gateway based on the Adafruit Feather 32u4 FONA, we came up with a new design. It bases on an Arduino Mega 2560, an Adafruit FONA breakout board, an RTC, and an SD-card reader. The larger memory of the Arduino Mega allowed using not only the FONA modem but also SD card logging. So now, even if the gateway is not able to send the data to the web server, the data can still be stored on the SD card. All files are available on our Github repository. The new gateway was deployed in two buildings, and the results look quite promising: