Remote ID Transmitter¶

Remote ID Transmitter is a built-in Linux application used to continuously broadcast identification and flight data. Remote ID broadcast is a standard in its own right and is required on most drones.

For more information, see the ARK Electronics RemoteIDTransmitter project.

Usage¶

The Remote ID Transmitter (rid-transmitter) is preinstalled on the Linux image. It must be connected to a PX4 instance. This document uses PX4 SITL (simulated); the same steps may apply to PX4 running on the Cortex-M7 core. The broadcast signal can be received using a phone with a mobile app such as Drone Scanner or with BLE sniffers.

1. PX4 SITL¶

In this setup, PX4 runs in simulation on a separate Linux PC (x86 architecture). The same steps may apply when installing directly on the board. The board and the PC must be discoverable to each other over the network.

a. Installation¶

sudo apt update && sudo apt install -y git
git clone https://github.com/PX4/PX4-Autopilot.git --recursive
cd PX4-Autopilot
bash ./Tools/setup/ubuntu.sh --no-nuttx
PX4_HOME_LAT=44.4351428 PX4_HOME_LON=26.0537122 PX4_HOME_ALT=80 make px4_sitl sihsim_quadx

If errors are encountered: OSRF repo “NOSPLIT / no longer signed” -> switch to HTTPS & Other dependencies

sudo rm -f /etc/apt/sources.list.d/gazebo-stable.list
sudo apt clean
sudo rm -rf /var/lib/apt/lists/*osrfoundation* /var/lib/apt/lists/partial/*
sudo wget https://packages.osrfoundation.org/gazebo.gpg -O /usr/share/keyrings/pkgs-osrf-archive-keyring.gpg
echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/pkgs-osrf-archive-keyring.gpg] https://packages.osrfoundation.org/gazebo/ubuntu-stable $(lsb_release -cs) main" | sudo tee /etc/apt/sources.list.d/gazebo-stable.list

sudo apt install -y \
  gz-jetty libunwind-dev cppzmq-dev \
  libopencv-dev libeigen3-dev protobuf-compiler \
  libgstreamer-plugins-base1.0-dev gstreamer1.0-plugins-base \
  gstreamer1.0-plugins-good gstreamer1.0-plugins-bad \
  gstreamer1.0-plugins-ugly gstreamer1.0-libav \
  libimage-exiftool-perl libxml2-utils dmidecode pkg-config bc

sudo apt update

b. Running¶

The coordinates can be changed as needed; those below are the coordinates of the Bucharest NXP site.

rm -rf build/px4_sitl_default
PX4_HOME_LAT=44.4351428 PX4_HOME_LON=26.0537122 PX4_HOME_ALT=80 make px4_sitl sihsim_quadx

MAVLink setup, required each time PX4 starts:

pxh> mavlink start -x -u 14555 -r 100000 -m onboard -o 14553 -t <BOARD-IP>
pxh> mavlink stream -r 5 -s OPEN_DRONE_ID_LOCATION -u 14555
pxh> mavlink stream -r 5 -s OPEN_DRONE_ID_SYSTEM   -u 14555
pxh> commander takeoff

2. RID-Transmitter¶

The commands below must be run as the root user (the Bluetooth and apt commands require it).

a. Setup¶

mkdir -p /opt/ark/share/rid-transmitter/
nano /opt/ark/share/rid-transmitter/config.toml

Text:

bluetooth_device  = "hci0"
connection_url    = "udpin://0.0.0.0:14553"
manufacturer_code = "MFR1" 
serial_number     = "950009500NXP" # any code is acceptable, provided it has the same length

b. Running¶

modprobe btnxpuart
hciconfig hci0 up
rid-transmitter

Expected startup output:

UAS Serial Number: MFR1...
Waiting for MAVSDK connection: udpin://0.0.0.0:14553
Connected to autopilot

The broadcast uses BLE Coded PHY. If a phone is used to listen for the broadcast, it might capture only the first message, depending on its Bluetooth capabilities, as not all phones support receiving on BLE Coded PHY.

In that case, the source code must be modified. See the next section.

3. Compiling rid-transmitter to broadcast on another BLE PHY¶

The steps below describe how to compile the application modified to broadcast on 1M PHY, which all Bluetooth devices support.

The steps below are for compiling on the board. Compilation can also be performed with the Yocto toolchain on an external computer; this document does not cover cross compilation.

a. MAVSDK¶

cd /home/user/
git clone --recursive https://github.com/mavlink/MAVSDK.git -b v3.12.0
cd MAVSDK
cmake -Bbuild/default -H. -DCMAKE_BUILD_TYPE=Release \
      -DBUILD_MAVSDK_SERVER=OFF \
      -DCMAKE_INSTALL_PREFIX=/usr/local/MAVSDK/install
cmake --build build/default -j$(nproc)
cmake --build build/default --target install

b. BlueZ¶

cd /home/user/
wget https://mirrors.edge.kernel.org/pub/linux/bluetooth/bluez-5.72.tar.xz
tar xf bluez-5.72.tar.xz
mkdir -p /usr/include/bluetooth
cp bluez-5.72/lib/*.h /usr/include/bluetooth/

cd ~/bluez-5.72
echo '#define VERSION "5.72"' > config.h
gcc -c -fPIC -O2 -I. -Ilib lib/bluetooth.c lib/hci.c lib/sdp.c lib/uuid.c
ar rcs /usr/lib/libbluetooth.a bluetooth.o hci.o sdp.o uuid.o
mkdir -p /usr/local/lib/pkgconfig
nano /usr/local/lib/pkgconfig/bluez.pc

Text:

prefix=/usr
exec_prefix=${prefix}
libdir=${prefix}/lib
includedir=${prefix}/include

Name: BlueZ
Description: Bluetooth protocol stack for Linux
Version: 5.72
Libs: -L${libdir} -lbluetooth
Cflags: -I${includedir}

After saving the file:

export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig:$PKG_CONFIG_PATH
pkg-config --modversion bluez

c. RemoteID Transmitter¶

cd /home/user
git clone --recursive https://github.com/ARK-Electronics/RemoteIDTransmitter.git
cd RemoteIDTransmitter

Modify the sources:

First modification:

File: src/Bluetooth/Bluetooth.cpp, le_set_extended_advertising_parameters()

The struct initialiser sets LE 1M, but two lines afterwards override it:

buf[20] = 0x03; // Primary_Advertising_PHY: 3 = LE Coded
buf[22] = 0x03; // Secondary_Advertising_PHY: 3 = LE Coded

Change both to 0x01:

sed -i 's/buf\[20\] = 0x03;/buf[20] = 0x01;/; s/buf\[22\] = 0x03;/buf[22] = 0x01;/' \
  src/Bluetooth/Bluetooth.cpp

Second modification:

File: src/Transmitter/Transmitter.cpp, run_state_machine() The transmit state machine alternates the advertising mode every 200 ms:

uint64_t loop_rate_ms = 200;
...
_toggle_legacy = !_toggle_legacy;
if (_toggle_legacy) {
    _bluetooth->enable_legacy_advertising();
} else {
    _bluetooth->enable_le_extended_advertising();
}

Change _toggle_legacy = !_toggle_legacy; to _toggle_legacy = true;

Build:

cmake -Bbuild -H. -DCMAKE_BUILD_TYPE=Release \
      -DCMAKE_C_FLAGS="-Wno-error=stringop-truncation"
cmake --build build -j$(nproc)

The new rid-transmitter can now be executed (ensure the config.toml file is present):

setcap 'cap_net_raw,cap_net_admin+eip' build/rid-transmitter
./build/rid-transmitter --config /opt/ark/share/rid-transmitter/config.toml