system_architecture.md

MotHub architecture and module layout

• Mosquitto mqtt server: Mqtt broker, auto-started on py boot.
• Every module is a python program using mqtt to sub/pub to topics

Topic list

These topics are the main topics available to pub/sub to, you can technically use custom topics, but undocumented topics are not recomended. All the documented topics are (should) be available in the MqttTopics from modules/mqtt_utils.py.

• speed: The boat's speed over ground, whether gps or calculated or otherwise.
• direction: The direction the boat is pointing/heading to. usually from gps or calculated.
• orientation: The 3 axis orientation of the boat in space (heel, roll, etc.).
• position: The geographical position of the boat in gps coordinates.
• wind_speed: The speed of the wind.
• wind_direction: The direction of the wind.
• strength: The strength data for strength/tension/etc. sensors. Needs to be formated with either the measurement type.

Making a module

Here are basic module example for both pub and sub modules.

Sub module

This sub module reads json data and displays it. The given callback method has to have the client, userdata, msg parameters.

import json
import paho.mqtt.client as mqtt
# Relative imports assuming this is in the modules folder.
from ..mqtt_modules import MqttSubModule 

class DemoSub(MqttSubModule):
    def __init__(self):
        super().__init__(mqtt_topic="demo")

        # Register callback methods that the client will call on getting data.
        self.register_client_callback("demo", self.on_message)

    def on_message(self, client: mqtt.Client, userdata, msg: mqtt.MQTTMessage):
        # msg.payload is a json string with a known format.
        data = json.loads(msg.payload) 
        print(f"Name: {data["name"]}, Type: {data["type"]}")

Pub module

This pub module sends Hello World to the topic when run() is called.

import json
import paho.mqtt.client as mqtt
# Relative imports assuming this is in the modules folder.
from ..mqtt_modules import MqttPubModule 

class DemoPub(MqttPubModule):
    def __init__(self):
        super().__init__(mqtt_topic="demo")

    def run(self):
        self.publish("demo", "Hello World")