From b1bb34a0cc619fcda6b5a467d819cb5411f8ce44 Mon Sep 17 00:00:00 2001
From: Arnav Shah <sarn248@gmail.com>
Date: Wed, 23 Oct 2024 19:55:51 -0400
Subject: [PATCH] Create MQTT.md

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+# Using MQTT To Communicate Between Jetson and Laptop
+
+> [!WARNING]  
+> This guide assumes you have a Jetson and a laptop connected to the same network and that static IP addresses are used for both devices. If you do not have a static IP address, please follow the guide static ip guide [here](https://google.com).
+
+## Install MQTT on Jetson
+1. Install the MQTT broker on Jetson
+   
+    ```bash
+    sudo apt-get install mosquitto
+    ```
+
+2. Install the MQTT client on Jetson (this is a fast way to verify MQTT broker is working)
+
+    ```bash
+    sudo apt-get install mosquitto-clients
+    ```
+
+3. Configure the MQTT broker to allow anonymous access and to listen on all interfaces
+
+    ```bash
+    sudo nano /etc/mosquitto/mosquitto.conf
+    ```
+
+    Add the following lines to the configuration file
+
+    ```
+    allow_anonymous true
+    listener 1884 0.0.0.0
+    ```
+
+4. Restart the MQTT broker to use the new configuration
+
+    ```bash
+    sudo systemctl restart mosquitto
+    ```
+> [!TIP]
+> If the mosquitto service is not running, you can start it using the following command
+> ```bash
+> sudo mosquitto -c /etc/mosquitto/mosquitto.conf  
+> ```
+
+5. Verify the MQTT broker is running
+
+    ```bash
+    systemctl status mosquitto
+    ```
+    or
+    ```bash
+    ps -ef | grep mosquitto
+    ```
+6. Test the MQTT broker by subscribing to a topic (must be done on two separate terminals)
+
+    ```bash
+    mosquitto_sub -t test
+    ```
+
+    In a new terminal, publish a message to the topic
+
+    ```bash
+    mosquitto_pub -t test -m "Hello MQTT"
+    ```
+
+    The message should appear in the terminal where you subscribed to the topic
+
+
+## Install MQTT on Laptop
+1. Install MQTT client on laptop
+
+    ```bash
+    sudo apt-get install mosquitto-clients
+    ```
+2. Subscribe to the same topic as the Jetson
+
+    ```bash
+    mosquitto_sub -h <Jetson IP> -t test
+    ```
+3. Publish a message from the laptop to the Jetson
+
+    ```bash
+    mosquitto_pub -h <Jetson IP> -t test -m "Hello from Laptop"
+    ```
+    The message should appear in the terminal where you subscribed to the topic on the Jetson
+
+## Using MQTT in Python
+1. Install the Python MQTT client on both the Jetson and Laptop
+
+    ```bash
+    pip install paho-mqtt
+    ```
+
+2. Create a Python script to publish a message to the Jetson
+
+    ```python
+    import paho.mqtt.client as mqtt
+    import json
+
+    MQTT_BROKER = "<Jetson IP>"
+    MQTT_PORT = 1884
+    MQTT_TOPIC = "test"
+
+    client = mqtt.Client(mqtt.allbackAPIVersion.VERSION1)
+    client.connect(MQTT_BROKER, MQTT_PORT)
+
+    data = {"key": "value"}
+    client.publish(MQTT_TOPIC, json.dumps(data))
+
+    client.disconnect()
+    ```
+3. Create a Python script to subscribe to the Jetson
+
+    ```python
+    import paho.mqtt.client as mqtt
+    import json
+
+    MQTT_BROKER = "<Jetson IP>"
+    MQTT_PORT = 1884
+    MQTT_TOPIC = "test"
+
+    def on_message(client, userdata, message):
+        data = json.loads(message.payload)
+        print(data)
+
+    client = mqtt.Client(mqtt.allbackAPIVersion.VERSION1)
+    client.connect(MQTT_BROKER, MQTT_PORT)
+    client.subscribe(MQTT_TOPIC)
+    client.on_message = on_message
+
+    client.loop_forever()
+    ```
+4. Run the publisher script on the Jetson and the subscriber script on the Laptop.
+
+
+## Troubleshooting
+1. If the subscriber is not receiving messages, check the IP address of the Jetson and the laptop. The IP address should be static and on the same network.
+2. If the subscriber is not receiving messages, check the MQTT broker configuration on the Jetson. The broker should allow anonymous access and listen on all interfaces.
+   
+
+## References
+1. [MQTT](https://mqtt.org/)
+2. [Mosquitto](https://mosquitto.org/)
+3. [Paho MQTT](https://github.com/eclipse/paho.mqtt.python)
+4. [Communicate between two Devices using MQTT](https://mohamedelhlafi.medium.com/use-the-mqtt-protocol-to-communicate-data-between-2-raspberry-pi-3d432dea9313)
+