ertnode is an application that performs the actual tracking: it should be run in a device attached to the object that
needs to be tracked, e.g. a weather balloon or a vehicle. It collects telemetry data and takes photographs
(currently only with Raspberry Pi camera) and transmits them using LoRa radio modulation to
The current design consists of concurrently running threads performing data collection and data transmissions simultaneously and independently. This design allows independent configuration of data collection and transmission intervals/schedules, so that the application may store more fine-grained telemetry and image data locally than what it transmits to receivers.
There are two data collection threads in the application:
Telemetry data collector, which logs the collected telemetry to local disk
Image capture routine, which takes photographs and saves them to local disk
The respective data transmission threads are:
Telemetry sender, serializing the latest piece of telemetry data to MsgPack format and transmitting via radio
Image sender, transmitting a resized thumbnail version of the latest image captured
The transmission threads may transmit data simultaneously, so packets containing telemetry and image data will be interleaved in the radio transmissions.
In order to improve chances for successfully received telemetry data messages, there are two types of messages sent by the telemetry sender: messages with full data and description strings and messages with only the GPS data and a couple of sensor readings without string descriptions. The former amounts currently to about 1000 bytes of data, which results in 4 LoRa packets to be transmitted, and the latter, abbreviated telemetry data message is designed to fit in one 251-byte packet payload. The possibility of successfully receiving one of these one-packet messages is significantly higher than data spanning multiple packets, especially when the received radio signal is very weak.
In addition to the tracking-related functionality,
ertnode runs also the same web server as
providing HTTP and WebSocket APIs to monitor and inspect the data it transmits in real time. The
web UI can be used with
ertnode, although it is mainly useful for testing and debugging purposes.
The minimum hardware requirements for running
A Raspberry Pi model A+, B+, Zero, 2B or 3B (any model with 40-pin GPIO connector)
Other single-board computers can be used by implementing support for accessing GPIO pins and registering GPIO interrupts.
A GPS receiver supported by
gpsd— any receiver outputting NMEA format data through serial port should work.
For example: Raspberry Pi GPS HAT from ModMyPi
A Semtech SX127x / HopeRF RFM9xW LoRa transceiver connected to Raspberry Pi SPI port.
Additionally LoRa chip DIO0 and DIO5 interrupts need to be exposed through Raspberry Pi GPIO pins.
For example: Raspberry Pi+ LoRa™ Expansion Board from Uputronics
Optional: I2C sensors supported by RTIMULib, such as the ones in Raspberry Pi Sense HAT
Optional: A Raspberry Pi camera connected via the CSI port
Support for other cameras is very easy to implement
These installation instructions are for Raspberry Pi and Raspbian, but most of it should work on any distribution. The main difference between distributions is usually just how the dependencies and libraries are installed.
Install library and tool dependencies:
apt-get install cmake make gcc git apt-get install ntp gpsd libgps21 libgps-dev libyaml-0-2 libyaml-dev apt-get install libraspberrypi-bin webp imagemagick jq
Raspberry Pi configuration
Enable peripheral interfaces in Raspberry Pi by adding the following to
# Enable I2C dtparam=i2c_arm=on # Enable SPI dtparam=spi=on # Enable serial port UART for GPS enable_uart=1 # Enable use of PPS time signal through GPIO (if exposed by GPS receiver) dtoverlay=pps-gpio,gpiopin=4 # Enable Raspberry Pi camera start_x=1
GPSd and NTP configuration
Configure GPSd to use Raspberry Pi internal serial port (assuming GPS is connected to it).
Replace the contents of file
/etc/default/gpsd with the following configuration:
# Default settings for the gpsd init script and the hotplug wrapper. # Start the gpsd daemon automatically at boot time START_DAEMON="true" # Use USB hotplugging to add new USB devices automatically to the daemon USBAUTO="true" # Devices gpsd should collect to at boot time. # They need to be read/writeable, either by user gpsd or the group dialout. DEVICES="/dev/ttyAMA0" # Other options you want to pass to gpsd GPSD_OPTIONS="-n"
The time data and signals from a GPS receiver can be used to feed the NTP daemon, so that Raspberry Pi can keep correct time as long as it has GPS lock.
Some GPS receivers expose PPS signal, which can be fed to Raspberry Pi GPIO for extra accuracy. There is more information about using PPS signal on these sites. To use the PPS signal, an additional utility needs to be installed:
git clone https://github.com/flok99/rpi_gpio_ntpd.git cd rpi_gpio_ntpd make sudo make install
Run the utility at boot time by adding the following to
# Use GPIO18 (pin 12) for GPS PPS signal /usr/local/bin/rpi_gpio_ntp -N 1 -g 18
Add the following configuration to
# GPS Serial data reference server 127.127.28.0 minpoll 4 maxpoll 4 fudge 127.127.28.0 time1 0.0 refid GPS # GPS PPS reference server 127.127.28.1 minpoll 4 maxpoll 4 prefer fudge 127.127.28.1 refid PPS
Enable GPSd and NTP daemon by executing:
systemctl enable gpsd systemctl start gpsd systemctl enable ntp systemctl start ntp
Reboot Raspberry Pi to make all config changes take effect.
Check out source code and build it:
git clone https://github.com/mikaelnousiainen/ert.git mkdir -p build/ertnode cd build/ertnode cmake ../../ert/ertnode make
Configure the application by editing
ertnode.yaml in the
sudo with root privileges, which are needed for GPIO access)
./ertnode-start-dev.sh # Run on foreground ./ertnode-start.sh # Run as a background daemon