Need advice on best method to add and log custom parameters from companion computer

Hi All,

I’m just getting started on a project where I want to make humidity/and temp measurements at various altitudes. I’ve currently done it with dual radio links, one for ardupilot telemetry, and the other was my humidity/temp data (coming from a RPI zero). On the ground I used mission planner NEMA output to obtain altitudes and time, I then made a user app that parsed out time/altitude/humidity/temperature from their respective serial ports, displayed the data, and more importantly recorded it. This set up required 2 laptops because of the number of available usb/serial ports on my computers and the number of usb2serial adapters required.

What I really want to do is create additional parameters for humidity and temperature, have the RPI zero update those parameters at ~1Hz via the telem2 port on my pixhawk 2.1, download the flight logs obtain the data but most importantly be able to see the temp/humidity data real time in Mission planner. That way I can get rid of the additional 900MHz radio, remove a laptop from the setup and get rid of a lot of serial to usb adapters.

I’m probably most familiar with python as a programming language. As I said, I’ll be interfacing to the FC with a rpi zero over the uart. I understand i’ll need to create the parameters on the FC and somehow get the rpi to send temp/humidity messages to the FC. How do I go about doing that? Which of these tools do I need: pymavlink, mavproxy, dronekit, maverick??
Can anyone tell me where I should start or a block diagram of how it might work programmatically?

Thanks Very much!


1 Like

Wouldn’t it be easier to take the ardupilot telemetry to the pi zero over a serial connection, and then forward this through the pi zero radio link as well as your humidity/temp data?

I really don’t know, I don’t know where to begin really. However I would rather record on the craft so the data is available even if the radio link gets degraded or drops out, additionally I think I may use missionplanner to plot the data as well, via the log analysis tools.


Were you able to figure this out? I’m working on something very similar and wanted to see if you made any progress that would help me.

This is doable by connecting your companion computer to the FC’s telem2 port and assembling + sending MAVlink packets via that port. When you send the packets, you need to specify a sysid and a compid. You can use sysid=1 and a compid that matches your onboard companion computer’s role. Here’s an example in C++/Arduino from an earlier project I worked on, which sends data using MAVlink DEBUG_VECT messages:

void DataRelay::SendSensorData(std::pair<int, int> smell)
    mavlink_message_t msg;
    uint8_t buf[MAVLINK_MAX_PACKET_LEN];

    // Pack a mavlink debug message to encode the sensor data
        /*sysid*/ 1,
        /*compid*/ MAV_COMP_ID_PATHPLANNER,
        /*name*/ "SENSOR",
        /*time_boot_ms*/ millis(),
        /*x*/ smell.first,
        /*y*/ smell.second,
        /*z*/ 0

    // Copy the message to the send buffer
    uint16_t len = mavlink_msg_to_send_buffer(buf, &msg);
    // Send the message via Serial1 to the FC's TELEM2 UART 
    Serial1.write(buf, len);


At the GCS, you will be able to see the MAVlink DEBUG_VECT messages under the compid associated with your companion computer. You can take those apart and analyze the data as needed. Here’s an example in python, running as a script in MissionPlanner:

def PacketHandler(o, message):
    global _log
    global _samples
    global _uav


        # Debug_vect packets. These are sent by component 195 and encode sensor values.
        if (message.msgid == MAVLink.MAVLINK_MSG_ID.DEBUG_VECT.value__) and \
            ("SENSOR" in bytes(
            # do whatever you want here with this data...
            _samples.collect(, cs.lng, cs.alt, cs.nav_bearing,,
            _log.Log("DEBUG_VECT/SENSOR: (" + str(_samples[-1].left) + "," + str(_samples[-1].right) + ")", VERBOSITY_MEDIUM)

    except Exception as inst:
        print inst

# somewhere in the init code...
# Subscribe to MAVlink messages
MAV.OnPacketReceived += PacketHandler

Let me know if I misunderstood what you want to do…