Building an Exhaustive ADS-B Feeder Station with Buildroot on Raspberry Pi 3

This guide explains how to build a professional-grade ADS-B station on a Raspberry Pi 3. We are using Buildroot to create a custom Linux firmware that is ultra-lightweight, boots in seconds, runs entirely in RAM (read-only) to prevent SD card corruption, and features automatic process supervision.

1. Project Architecture

We use the BR2_EXTERNAL mechanism to keep our custom logic clean and portable. First, clone the stable Buildroot source:

git clone https://gitlab.com/buildroot.org/buildroot.git
cd buildroot
git checkout 2025.02.13

Our project tree is organized as follows to streamline building and deployment:

.
├── Makefile               # <--- Root wrapper for easy building
├── upload.sh              # <--- Automated deployment script
├── device_table_custom.txt# <--- Custom file permissions rules
├── buildroot/             # Official sources (git clone)
├── external-pi/           # Custom recipes layer
│   ├── Config.in
│   ├── external.desc
│   ├── external.mk
│   ├── board/             # <--- Boot configs (config.txt, cmdline.txt)
│   └── package/
│       ├── librtlsdr-blog/
│       ├── mlat-client/
│       └── readsb/
└── overlay/               # System files (Init, Network, Configs)
    ├── etc/
    │   ├── fr24feed.ini
    │   ├── monitrc        # <--- Process watchdog config
    │   ├── init.d/
    │   │   ├── S50readsb
    │   │   ├── S60fr24
    │   │   ├── S99mlat-client-adsbfi
    │   │   └── S99mlat-client-adsbx
    │   ├── lighttpd/
    │   ├── modprobe.d/
    │   ├── network/
    │   └── wpa_supplicant.conf
    ├── usr/bin/fr24feed
    └── var/www/tar1090

To make compilation easier, create a wrapper Makefile at the root of your project:

Makefile:

BR2_EXTERNAL_PATH := $(CURDIR)/external-pi

all:
	$(MAKE) -C buildroot BR2_EXTERNAL=$(BR2_EXTERNAL_PATH)

%:
	$(MAKE) -C buildroot BR2_EXTERNAL=$(BR2_EXTERNAL_PATH) $@

Now, you can simply type make menuconfig or make from the root folder.

2. The External Layer (external-pi)

These files declare the project to Buildroot:

external-pi/external.desc:

name: PI_FEEDER_EXT
desc: Station ADS-B pour Pi3

external-pi/external.mk:

include $(sort $(wildcard $(BR2_EXTERNAL_PI_FEEDER_EXT_PATH)/package/*/*.mk))

external-pi/Config.in (Menu integration):

source "$BR2_EXTERNAL_PI_FEEDER_EXT_PATH/package/librtlsdr-blog/Config.in"
source "$BR2_EXTERNAL_PI_FEEDER_EXT_PATH/package/readsb/Config.in"
source "$BR2_EXTERNAL_PI_FEEDER_EXT_PATH/package/mlat-client/Config.in"

3. Software Recipes & Compilation

A. Optimized Drivers: librtlsdr-blog

external-pi/package/librtlsdr-blog/Config.in:

config BR2_PACKAGE_LIBRTLSDR_BLOG
	bool "librtlsdr-blog"
	select BR2_PACKAGE_LIBUSB
	help
	  Version optimisée pour RTL-SDR Blog V4 avec support Bias-T.

	  https://github.com/rtlsdrblog/rtl-sdr-blog

external-pi/package/librtlsdr-blog/librtlsdr-blog.mk:

LIBRTLSDR_BLOG_VERSION = master
LIBRTLSDR_BLOG_SITE = $(call github,rtlsdrblog,rtl-sdr-blog,$(LIBRTLSDR_BLOG_VERSION))
LIBRTLSDR_BLOG_LICENSE = GPL-2.0+
LIBRTLSDR_BLOG_INSTALL_STAGING = YES

LIBRTLSDR_BLOG_DEPENDENCIES = libusb

# On active explicitement le détachement du driver kernel (DVB-T) 
# et l'installation des outils (rtl_sdr, rtl_biast, etc.)
LIBRTLSDR_BLOG_CONF_OPTS = \
	-DINSTALL_UDEV_RULES=ON \
	-DDETACH_KERNEL_DRIVER=ON

$(eval $(cmake-package))

B. The Decoder: readsb

external-pi/package/readsb/Config.in:

config BR2_PACKAGE_READSB
	bool "readsb"
	select BR2_PACKAGE_LIBRTLSDR_BLOG
	select BR2_PACKAGE_NCURSES
	select BR2_PACKAGE_ZLIB
	select BR2_PACKAGE_ZSTD
	help
	  Readsb est un décodeur ADS-B haute performance.

external-pi/package/readsb/readsb.mk:

READSB_VERSION = master
READSB_SITE = $(call github,wiedehopf,readsb,$(READSB_VERSION))
READSB_DEPENDENCIES = librtlsdr-blog ncurses zlib zstd
READSB_LICENSE = GPL-3.0

# On utilise le hook SED pour les versions
define READSB_FIX_VERSION_MACROS
	sed -i 's/READSB_SHORT_VERSION/"2025"/g' $(@D)/json_out.c
	sed -i 's/READSB_SHORT_COMMIT/"v4"/g' $(@D)/json_out.c
endef
READSB_POST_PATCH_HOOKS += READSB_FIX_VERSION_MACROS

# On passe RTLSDR=yes ET on force le flag de compilation manuellement dans CFLAGS
READSB_MAKE_OPTS = \
	RTLSDR=yes \
	CFLAGS="$(TARGET_CFLAGS) -D_GNU_SOURCE -D_DEFAULT_SOURCE -DENABLE_RTLSDR"

define READSB_BUILD_CMDS
	$(TARGET_MAKE_ENV) $(MAKE) $(TARGET_CONFIGURE_OPTS) -C $(@D) $(READSB_MAKE_OPTS)
endef

define READSB_INSTALL_TARGET_CMDS
	$(INSTALL) -D -m 0755 $(@D)/readsb $(TARGET_DIR)/usr/bin/readsb
	$(INSTALL) -D -m 0755 $(@D)/viewadsb $(TARGET_DIR)/usr/bin/viewadsb
endef

$(eval $(generic-package))

C. MLAT Client

external-pi/package/mlat-client/Config.in:

config BR2_PACKAGE_MLAT_CLIENT
	bool "mlat-client"
	depends on BR2_PACKAGE_PYTHON3
	select BR2_PACKAGE_PYTHON_PYASYNCORE
	select BR2_PACKAGE_PYTHON_PYASYNCHAT²
	select BR2_PACKAGE_PYTHON3_ZLIB
	help
	  Mode S Multilateration client for ADS-B feeders.

	  https://github.com/mutability/mlat-client

comment "mlat-client needs python3"
	depends on !BR2_PACKAGE_PYTHON3

external-pi/package/mlat-client/mlat-client.mk:

MLAT_CLIENT_VERSION = 0.2.13
MLAT_CLIENT_SITE = $(call github,mutability,mlat-client,v$(MLAT_CLIENT_VERSION))
MLAT_CLIENT_LICENSE = GPL-3.0
MLAT_CLIENT_LICENSE_FILES = COPYING
MLAT_CLIENT_SETUP_TYPE = setuptools

$(eval $(python-package))

4. System Configuration (Overlay)

The overlay directory contains custom configuration files and pre-compiled binaries that are merged into the final root filesystem.

Note: Some binaries like fr24feed and the tar1090 web interface files should be placed manually in the overlay/ directory before building if they are not managed by a Buildroot recipe.

Device Table Customization (Required for Monit)

We use Monit for process supervision, which strictly requires its configuration file to have 0600 permissions. We enforce this at the Buildroot generation level using a custom device table.

device_table_custom.txt (at project root):

# <name>        <type>  <mode>  <uid>   <gid>   <major> <minor> <start> <inc> <count>
/etc/monitrc    f       600     0       0       -       -       -       -       -

You must link this file in make menuconfig under System configuration -> Path to the permission tables (e.g., system/device_table.txt $(BR2_EXTERNAL_PI_FEEDER_EXT_PATH)/../device_table_custom.txt).

Network & WiFi

overlay/etc/network/interfaces:

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet dhcp

auto wlan0
iface wlan0 inet dhcp
    pre-up sleep 2
    wpa-conf /etc/wpa_supplicant.conf

overlay/etc/wpa_supplicant.conf:

country=FR
network={
    ssid="YOUR_SSID"
    psk="YOUR_PASSWORD"
}

overlay/etc/modprobe.d/rtlsdr-blacklist.conf:

blacklist dvb_usb_rtl28xxu
blacklist rtl2832
blacklist rtl2830

Init Scripts (The Automation)

overlay/etc/init.d/S50readsb (The Core Decoder):

#!/bin/sh

DAEMON="readsb"
BINARY="/usr/bin/readsb"
SITE_UUID="YOUR_UUID"

ARGS="--device-type rtlsdr \
      --net \
      --fix \
      --dcfilter \
      --lat YOUR_LAT \
      --lon YOUR_LON \
      --net-ri-port 0 \
      --net-ro-port 30002 \
      --net-bi-port 30004 \
      --net-bo-port 30005 \
      --write-json /tmp/readsb \
      --net-connector feed.adsb.fi,30004,beast_reduce_out,uuid=$SITE_UUID \
      --net-connector feed.adsbexchange.com,30004,beast_reduce_out"

case "$1" in
    start)
        echo -n "Starting $DAEMON: "
        /usr/bin/rtl_biast -b 1 > /dev/null 2>&1
        sleep 1
        start-stop-daemon -S -b -x $BINARY -- $ARGS
        [ $? -eq 0 ] && echo "OK" || echo "FAIL"
        ;;
    stop)
        echo -n "Stopping $DAEMON: "
        start-stop-daemon -K -x $BINARY
        [ $? -eq 0 ] && echo "OK" || echo "FAIL"
        ;;
    restart)
        $0 stop
        sleep 1
        $0 start
        ;;
    *)
        echo "Usage: $0 {start|stop|restart}"
        exit 1
        ;;
esac

overlay/etc/init.d/S99mlat-client-adsbx (Feed ADSBExchange):

#!/bin/sh
NAME="mlat-client-adsbx"
DAEMON="/usr/bin/mlat-client"
PIDFILE="/var/run/$NAME.pid"

ARGS="--input-type dump1090 \
      --input-connect 127.0.0.1:30005 \
      --lat YOUR_LAT \
      --lon YOUR_LON \
      --alt 45m \
      --user YOUR_USER \
      --server feed.adsbexchange.com:31090 \
      --no-udp \
      --results beast,connect,127.0.0.1:30004"

case "$1" in
  start)
        echo -n "Starting $NAME: "
        start-stop-daemon -S -q -b -m -p $PIDFILE -x $DAEMON -- $ARGS
        echo "OK"
        ;;
  stop)
        echo -n "Stopping $NAME: "
        start-stop-daemon -K -q -p $PIDFILE
        echo "OK"
        rm -f $PIDFILE
        ;;
  restart)
        $0 stop
        sleep 1
        $0 start
        ;;
  *)
        echo "Usage: $0 {start|stop|restart}"
        exit 1
        ;;
esac

overlay/etc/init.d/S99mlat-client-adsbfi (Feed ADSB.fi):

#!/bin/sh
NAME="mlat-client-adsbfi"
DAEMON="/usr/bin/mlat-client"
PIDFILE="/var/run/$NAME.pid"

ARGS="--input-type dump1090 \
      --input-connect 127.0.0.1:30005 \
      --lat YOUR_LAT \
      --lon YOUR_LON \
      --alt 45m \
      --user YOUR_USER \
      --server feed.adsb.fi:31090 \
      --no-udp \
      --results beast,connect,127.0.0.1:30004"

case "$1" in
  start)
        echo -n "Starting $NAME: "
        start-stop-daemon -S -q -b -m -p $PIDFILE -x $DAEMON -- $ARGS
        echo "OK"
        ;;
  stop)
        echo -n "Stopping $NAME: "
        start-stop-daemon -K -q -p $PIDFILE
        echo "OK"
        rm -f $PIDFILE
        ;;
  restart)
        $0 stop
        sleep 1
        $0 start
        ;;
  *)
        echo "Usage: $0 {start|stop|restart}"
        exit 1
        ;;
esac

overlay/etc/init.d/S60fr24 (FlightRadar24 Feed):

#!/bin/sh
DAEMON="fr24feed"
BINARY="/usr/bin/fr24feed"

case "$1" in
    start)
        echo -n "Starting $DAEMON: "
        sleep 2
        start-stop-daemon -S -b -x $BINARY
        [ $? -eq 0 ] && echo "OK" || echo "FAIL"
        ;;
    stop)
        echo -n "Stopping $DAEMON: "
        start-stop-daemon -K -x $BINARY
        [ $? -eq 0 ] && echo "OK" || echo "FAIL"
        ;;
    restart)
        $0 stop
        sleep 1
        $0 start
        ;;
    *)
        echo "Usage: $0 {start|stop|restart}"
        exit 1
        ;;
esac

Process Supervision (Monit)

If fr24feed crashes or stops responding on its HTTP port, Monit will automatically restart it.

overlay/etc/monitrc:

set daemon 60
set log syslog
set httpd port 2812
    use address 0.0.0.0
    allow localhost
    allow 192.168.1.0/24

check process fr24feed matching "/usr/bin/fr24feed"
    start program = "/etc/init.d/S60fr24 start"
    stop program  = "/etc/init.d/S60fr24 stop"
    if failed host 127.0.0.1 port 8754 protocol http for 2 cycles then restart

Feeder Configurations

overlay/etc/fr24feed.ini:

receiver="beast-tcp"
fr24key="YOUR_FR24_KEY"
host="127.0.0.1:30005"
bs="no"
raw="no"
logmode="1"
logpath="/tmp"
mlat="yes"
mlat-without-gps="yes"

overlay/etc/lighttpd/lighttpd.conf (Web Interface):

server.modules += ( "mod_alias", "mod_setenv" )
server.document-root        = "/var/www/tar1090"
server.port                 = 80
index-file.names            = ( "index.html" )

mimetype.assign = (
  ".html" => "text/html",
  ".css"  => "text/css",
  ".js"   => "application/javascript",
  ".json" => "application/json",
  ".png"  => "image/png",
  ".svg"  => "image/svg+xml"
)

alias.url += ( "/data/" => "/tmp/readsb/" )

$HTTP["url"] =~ "^/data/" {
    setenv.add-response-header = ( "Cache-Control" => "no-cache, no-store, must-revalidate" )
}

5. RAM-Only Boot Configuration

To run the OS entirely in RAM, we use the initramfs strategy. This loads the rootfs.cpio.gz into the Raspberry Pi’s memory at boot time. You have two options to implement this:

Method A: Automated (Buildroot Integration)

This is the professional way. The files are generated correctly every time you run make.

Prepare your custom board files: Create a folder external-pi/board/ and create two files:

external-pi/board/config.txt:

# RAM Boot Config
kernel=zImage
initramfs rootfs.cpio.gz followkernel
# Enable UART for console
enable_uart=1

external-pi/board/cmdline.txt:

console=serial0,115200 console=tty1 root=/dev/ram0 rw rootwait

Configure Buildroot (make menuconfig):
- Filesystem images:
  - Enable cpio the root file system.
  - Compression: gzip.
- Target packages -> Hardware handling:
  - Select rpi-firmware.
  - Set Configuration file to $(BR2_EXTERNAL_PI_FEEDER_EXT_PATH)/board/config.txt.
- System configuration:
  - Set Custom scripts to run after creating the images to point to a script that copies your cmdline.txt to the output folder.

Method B: Manual (Quick Edit on SD Card)

If you don’t want to touch Buildroot files, you can edit the files on the SD card after flashing.

Flash the SD card as described in Section 7.
Mount the BOOT partition on your PC.
Edit config.txt: Add the line initramfs rootfs.cpio.gz followkernel.
Edit cmdline.txt: Replace the content with console=serial0,115200 console=tty1 root=/dev/ram0 rw rootwait.

6. Buildroot Setup Checklist

Enable these options in make menuconfig to match our project’s requirements:

Target options: Cortex-A53, NEON-VFPV4, Hard float (EABIhf), instructions ARM.
Toolchain: Glibc library, Linux Headers 6.6.x, GCC 13.x, Binutils 2.43.x. Enable Wchar, Locale, and C++ support.
Kernel: Custom Raspberry Pi kernel (bcm2709_defconfig) using the 6.6.y branch. Enable Device Tree support and DTB overlay support.
System Configuration:
- Root login enabled (password: root).
- DHCP enabled on eth0.
- BR2_ROOTFS_OVERLAY pointing to your overlay/ directory.
- Path to the permission tables pointing to $(BR2_EXTERNAL_PI_FEEDER_EXT_PATH)/../device_table_custom.txt.
WiFi Stack: linux-firmware -> Broadcom BCM43xxx & Cypress CYW43xxx.
Networking: lighttpd (with zlib), dropbear (SSH), wpa_supplicant (with nl80211), chrony (NTP sync).
Tools: monit, bash, python3 (with zlib, unicodedata, pyasyncore, pyasynchat), socat, kmod (tools), ca-certificates.
Libraries: libusb, ncurses, readline, zlib, zstd, xxhash.
Filesystem: cpio with gzip compression (disable TAR).

7. Deployment

Method A: Manual SD Formatting (First boot)

# Format 1 FAT32 partition on SD card
sudo mkfs.vfat -F 32 -n BOOT /dev/sdX1
# Copy boot images from output/images/
sudo cp buildroot/output/images/zImage buildroot/output/images/rootfs.cpio.gz buildroot/output/images/bcm2710-rpi-3-b.dtb buildroot/output/images/rpi-firmware/* /mnt/sdcard/

Method B: Automated Network Deployment (Fast Iteration)

Since the system runs in RAM, the SD card partition containing the kernel is typically not mounted. To speed up development iterations, we use an automated script to mount the partition over SSH, upload the new image, and reboot.

Create upload.sh at the root of your project:

#!/bin/sh

set -e

# Update this IP to match your Pi's address
IP="192.168.1.50"
TARGET="root@$IP"
BOOT="/boot"
IMAGE_DIR="buildroot/output/images"

echo "==> Montage de /boot..."
ssh "$TARGET" "mkdir -p $BOOT && mount /dev/mmcblk0p1 $BOOT 2>/dev/null || true"

echo "==> Upload de l'image..."
scp -O \
    "$IMAGE_DIR/zImage" \
    "$IMAGE_DIR/rootfs.cpio.gz" \
    "$IMAGE_DIR/bcm2710-rpi-3-b.dtb" \
    "$TARGET:$BOOT/"

echo "==> Synchronisation et reboot..."
ssh "$TARGET" "sync && reboot"

echo "==> Upload terminé, reboot en cours."

echo "==> Nettoyage SSH."
ssh-keygen -f '/home/ron/.ssh/known_hosts' -R "$IP"

echo "==> Terminé"

Make it executable (chmod +x upload.sh). After running make, just execute ./upload.sh to update your station over the network in seconds!

8. Results & Performance

Once the station is up and running, you can access the local web interface (tar1090) to view real-time traffic. The custom Buildroot firmware ensures extremely low CPU usage, no SD card wear, and Monit ensures the data keeps flowing even if a process crashes.

Figure 1: Local tar1090 interface showing live aircraft tracking.

Figure 2: ADS-B hits and positions reported to FlightRadar24.

Figure 3: Reception performance: hits vs. distance.

Figure 4: General feeder statistics on the FlightRadar24 dashboard.