• I need help with my setup. I know that arduplane can set up two out puts but im using arducopter. In my case im using the OpenLRS system transfer my telemetry to my tx and to the ground station. This set up only work 19200bud rate so i wanted another link with 54000bud to send it to my other radio and the OSD. Is this even possible or suck it up and change my minimosd bud rate to 19200bud?

  • Hi,

    There is no way without a recompile.

    And you have to do:


    in APM_Config.h .

    Besides that, for some reason I have never understood, there is a condition made to prevent UART2 telemetry if the multiplexer of APM2 is enabled. (The multiplexer is an electronic switch that switches UART0 between USB and the telemetry port, allowing one port to be used for both although not at the same time),

    UART2 has nothing to do with the multiplexer or with UART0 and the GCS code supports using 2 serial interfaces at the same time. MAVLink supports multiple links too so I don't understand the condition. Anyway here it is, in system.pde:

    #if USB_MUX_PIN > 0
    if (!usb_connected) {
    // we are not connected via USB, re-init UART0 with right
    // baud rate
    Serial.begin(map_baudrate(g.serial3_baud, SERIAL3_BAUD));
    // we have a 2nd serial port for telemetry
    Serial3.begin(map_baudrate(g.serial3_baud, SERIAL3_BAUD), 128, SERIAL_BUFSIZE);

    Just remove #if, #else and #endif to get both possibilities at the same time. It will work.

    It makes sense to have 2 serial ports at the same time, even with a multiplexer. Some people have multiple telemetry links, other have MAVLink eating hardware in board (OSDs etc) besides telemetry.

    Use the UART2 port at the side of the board. Much easier than having to set solder jumpers and having to figure if doing so will sabotage USB serial.

    If you wonder about this "Serial3" talk in the code: That name is legacy from APM1, where UART3 was used as secondary telemetry interface. So the fields in the code are still called Serial3 something, and the baud rate parameter is SERIAL3_BAUD. However when compiled for APM2, it all refers to UART2. APM2 uses the UART3 pins for SPI, and that is probably why it had to be moved to UART2.



  • I am not sure if this is wrong place to ask this question, but it is related to using UART2 instead of UART0, the thing is that I have been using minimOSD with APM 2.0 and everything works great, then all out of sudden it stopped working (just on my desk) and after some time trying to figure out I measured the resistanse on RX0 on APM2.0 to GND and it is only 2.3 ohm so it seems like I have broken the serial port or what do you think, I always get no heartbeat with mission pplanner and "waiting for heartbeat" on minimOSD.

    What I was thinking is if I could use any serialport other than UART0 to connect to the AMP 2.0? it seems all to be working except the UART0, (stabilisation and such seems to work) so I could use the apm just as it is but then I could not make new missions or change any configuration and I can not use minimOSD...

    just by using UART2 as telemetryport would be better than nothing but I don't know how to use that, I have made the solderjumper on the back of the APM but nothing happends

    What do you guys think? do I simply have to buy another APM?

  • I see the simplicity in just splitting a UART, but what if you want to just send a subset of the mavlink data on the second UART?  While I could have my payload sort through the complete telemetry feed and pick out what it wants, is having the APM make a tailored feed for that second UART possible?  Or will that tax the APM too much?

  • What about using UART2 for only ouput?  I could see this being useful for payloads that want position data from the APM, while still having a fully functional telemetry link to the ground.  Is this possible?

  • Tom, I don't think so.  What you have to do depends on your objective here.  The wiki explains how to route serial3 to UART2.  This tales a mod to APM_config.h and subsequent compilation.

    #define TELEMETRY_UART2 ENABLED  // solder bridge changed to enable UART2;

    Other related topics are discussed here Serial2-UART2

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Aug 25