Assignment 4: IMU Sensor and MQTT Communication

Navigate to workshops/2025-10-17 directory and open Assignment 4 in the MicroPython Jupyter Notebook browser interface.

If prompted with selecting kernel, select Embedded Kernel, click on the ESP Control Panel and connect your device.

In this assignment you will read orientation data from an ICM42670 IMU sensor and publish it to an MQTT broker.

Understanding IMU Sensors
#

An Inertial Measurement Unit (IMU) combines:

Accelerometer: Measures linear acceleration (including gravity)
Gyroscope: Measures rotational velocity
Temperature sensor: Measures device temperature

The ICM42670 is a 6-axis IMU (3-axis accelerometer + 3-axis gyroscope).

For more information about IMU sensors, visit the wiki page.

Understanding MQTT
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MQTT (Message Queuing Telemetry Transport) is a lightweight publish-subscribe messaging protocol ideal for IoT:

Broker: Central server that routes messages
Topics: Hierarchical message channels (e.g., sensors/imu/orientation)
QoS: Quality of Service levels (0, 1, or 2)

For more information about MQTT, visit the wiki page.

Subscribing to MQTT Topic
#

To subscribe to a topic, you will have two options:

HiveMQ Online MQTT Client
#

Navigate to HiveMQ and connect to the broker test.mosquitto.org on port 8081.
Under Subscriptions click on the Add New Topic Subscription, enter esp32/orientation and click on Subscribe

Mosquitto Client
#

Subscribe to the topic:
- On Linux or MacOS run command mosquitto_sub -h test.mosquitto.org -t "esp32/orientation" in your terminal to subscribe to the topic
- On Windows you will need to add mosquitto to your PATH environment variable or navigate to the path where the executable is located (usually C:\Program Files\mosquitto\) and run mosquitto_sub.exe -h test.mosquitto.org -t "esp32/orientation"

Task 1: Connect to Wi-Fi
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In this task, you’ll connect the ESP32 to your Wi-Fi network so it can communicate with the MQTT broker. The code waits until the connection is established and prints the network configuration.

SSID = "<WIFI_NAME>"
PASSWORD = "<WIFI_PASSWORD>"

sta = network.WLAN(network.STA_IF)
sta.active(True)
sta.connect(SSID, PASSWORD)

while not sta.isconnected():
    time.sleep(1)
    print("Connecting to Wi-Fi...")

print("Connected to Wi-Fi")
print(f"Network config: {sta.ifconfig()}")

Task 2: Initialize MQTT
#

Here you’ll create an MQTT client and connect it to a broker. You’ll publish orientation messages to the topic “esp32/orientation”.

BROKER = "test.mosquitto.org"
TOPIC = b"esp32/orientation"

client = MQTTClient("esp32client", BROKER)
client.connect()
print("Connected to MQTT broker")

Task 3: Initialize IMU
#

In this task, you’ll set up the ICM42670 IMU over I2C. You’ll configure the accelerometer and gyroscope full-scale range, data rate, and power mode for accurate measurements.

i2c = I2C(0, scl=Pin(8), sda=Pin(7), freq=400000)

# Create IMU instance
imu = ICM42670(i2c)

# Configure sensor
imu.configure(
    gyro_fs=GyroFS.FS_500DPS,
    gyro_odr=ODR.ODR_100_HZ,
    accel_fs=AccelFS.FS_4G,
    accel_odr=ODR.ODR_100_HZ
)

# Enable sensors
imu.set_accel_power_mode(PowerMode.LOW_NOISE)
imu.set_gyro_power_mode(PowerMode.LOW_NOISE)

Task 4: Read Orientation and Publish
#

Finally, you’ll read accelerometer and gyroscope data, compute orientation using a complementary filter, interpret the device’s tilt, and publish it to MQTT. The main loop prints the orientation locally and continuously sends updates to the broker.

def publish_orientation():
    """Read orientation and publish to MQTT"""

    while True:
        # Read sensor data
        data = imu.get_all_data()
        accel = (data['accel']['x'], data['accel']['y'], data['accel']['z'])
        gyro = (data['gyro']['x'], data['gyro']['y'], data['gyro']['z'])

        # Calculate orientation using complementary filter
        angles = imu.complementary_filter(accel, gyro)
        roll = angles['roll']
        pitch = angles['pitch']

        # Interpret orientation
        if abs(pitch) < 20 and abs(roll) < 20:
            position = "Flat"
        elif pitch > 30:
            position = "Tilted Forward"
        elif pitch < -30:
            position = "Tilted Backward"
        elif roll > 30:
            position = "Tilted Right"
        elif roll < -30:
            position = "Tilted Left"
        else:
            position = "Diagonal"

        # Create message
        message = f"Roll: {roll:.1f}°, Pitch: {pitch:.1f}° -> {position}"
        print(message)

        # Publish to MQTT
        client.publish(TOPIC, position.encode())

        time.sleep(0.5)

publish_orientation()