Subscribing to a telemetry message

The drone publishes all of its telemetry data as protobuf encoded messages transmitted via a ZeroMQ socket. You can find the protobuf message definitions in the Protocol Definitions repository, and the generated python definitions are located in the blueye.protocol repository.

Adding a callback

To add a callback we need to use the add_msg_callback function, and provide it with a list of telemetry messages types we want it to trigger on, as well as a function handle to call. All available telemetry messages can be found in telemetry.proto

Removing a callback

A callback is removed with remove_msg_callback using the ID returned when creating the callback.

Adjusting the publishing frequency of a telemetry message

By using the set_msg_publish_frequency function we can alter how often the drone should publish the specified telemetry message. The valid frequency range is 0 to 100 Hz.

Example

The following example illustrates how can use a callback to print the depth reported by the drone.

"""print_depth.py

This example program demonstrates how one can add a callback function to a telemetry message, as
well as how to adjust the frequency of that telemetry message, and how to remove the callback.
"""
import time

import blueye.protocol as bp

from blueye.sdk import Drone


def callback_depth(msg_type: str, msg: bp.DepthTel):
    """Callback for the depth telemetry message

    This function is called once for every DepthTel message received by the telemetry watcher
    """
    print(f"Got a {msg_type} message with depth: {msg.depth.value:.3f}")


if __name__ == "__main__":
    # Instantiate a drone object
    my_drone = Drone()

    # Add a callback for the DepthTel message, storing the ID for later use
    callback_id = my_drone.telemetry.add_msg_callback([bp.DepthTel], callback_depth)

    # Adjust the publishing frequency to 5 Hz
    my_drone.telemetry.set_msg_publish_frequency(bp.DepthTel, 5)

    # Callback is triggered by a separate thread while we sleep here
    time.sleep(5)

    # Remove the callback using the ID we stored when it was created (not really necessary here
    # since the my_drone object goes out of scope immediately afterwards)
    my_drone.telemetry.remove_msg_callback(callback_id)