In my home automation system I need to send alarms and events via SMS to my mobile number because an internet connection is not stable and may absent on power loss. Therefore I’ve purchased a compact board with the SIM900 chipset.
Note: SIM900A – this is an Asian version of this chip and does work in Europe. I’ve flashed the “1137B02SIM900M64” firmware and now it works well with my SIM cards. Here is the blog with many firmwares, flashing tools and instructions.
I’m using Pimatic and it does not have a ready-to-use plugin for this GSM modem. I’ve found a python code on the web that easily allows to send SMS using both ASCII and Unicode modes. My work is to create a daemon that will route MQTT messages to a SMS messages and vice versa. Pimatic has the very powerful MQTT plugin and I can send SMS messages using built-in rules.
Additionally I can process incoming SMS messages and execute commands from SMS messages by subscribing to a selected topic.