Lightweight IoT MQTT library for mobile network chips (so far just SIM800c)
This MQTT client library was born out of the seeming lack of documentation/support for the SIM800c GPRS chip. As of this writing, it is now January 2023 and GSM/GPRS is mostly phased out, and the SIM800c chip has been left in the dust - but it is still cheap and widely available, so hopefully this helps someone else get started.
I also tried to make the API as chip-agnostic as possible, so while there is only one implementation now, for the SIM800c, please feel free to roll your own for another chip and make a PR.
# Schedule library is required to run event-based commands while the forever-loop is running
import schedule
import logging
from datetime import datetime
from cellmqtt import CellMQTT, WirelessChip
# Initialize a CellMQTT instance with your wireless chip and desired log level
# > Values can be overridden here, but it is cleaner to configure them from
# > a config.ini in your project directory
cmqtt = CellMQTT(cell_chip=WirelessChip.SIM800C, log_level = logging.DEBUG)
# You can also override MQTT connection parameters:
# > cmqtt.connect(host='test.com', port=1883)
# > or, just use none and they will be pulled from config.ini:
cmqtt.connect()
def handle_test(topic: str, message: bytes):
print('------ GOT MSG FROM TOPIC: ' + topic + '! ------')
print(str(message, 'utf-8'))
print('------ END OF MESSAGE ------')
cmqtt.subscribe('ext/test', handle_test)
def publish_demo():
cmqtt.publish('ext/test/date', str(datetime.utcnow()))
schedule.every(40).seconds.do(publish_demo)
cmqtt.loop()There is a config-sample.ini file which should be renamed to config.ini. These values can also be overridden when initializing the CellMQTT class in your program.
There were a lot of great resources that helped me understand the workings of GSM/GPRS chips, serial connections, MQTT protocols, and more. Some are more relevant, some less, but all of the following were extremely helpful to me:
-
Adafruit CircuitPython_MiniMQTT This client library from Adafruit was really helpful to get an understanding of how MQTT clients work on a lower level.
-
MQTT Protocol tutorial using SIM900/SIM800 modules – MQTT over TCP - This blog post and associated YouTube video from Ravi Pujar was what gave me the initial boost of confidence that I could actually get this done with the
SIM800cmodule I had on hand. He does explain the underlying concepts, but there is definitely not much to copy/paste and get going here. -
WaveShare Wiki - SIM800C GSM/GPRS HAT - WaveShare, who makes the module that I have has a pretty decent documentation page.
-
usim800 python library - This library was what I was initially going to use to simply make HTTP requests - but it turned out to not really meet my needs - playing around with @Bhagyarsh library helped me gain a lot of understanding of the underlying AT commands for the SIM800c
-
MQTT Version 3.1.1 protocol docs - This is probably the single most important resource for understanding how MQTT actually works
-
mqtt-codec python library - Last, but absolutely not least, is the
mqtt-codeclibrary. Until I found this it was an absolute uphill battle for me to get MQTT packets correctly formed.