MQTT remote monitoring of temperature and humidity
GSM module instructions
http://www.instructables.com/id/GSMGPRS-Module-DIY-Kit/
GSM module (M590E) datasheet
http://cyntech.co.uk/downloads/neoway-m590-hardware-design-manual-v1.pdf
GSM module (M590E) AT commands
https://cdn.instructables.com/ORIG/FX6/UAHQ/IZ6CYGIU/FX6UAHQIZ6CYGIU.pdf
DHT library
https://github.com/winlinvip/SimpleDHT
TinyGSM library
https://github.com/vshymanskyy/TinyGSM
Low power regulator