Amilcar

This setup is designed to run on a Raspberry Pi, synchronizing its internal clock with GPS time and recording audio- files with timestamps of each second using a hydrophone. It is part of OpenSwarm project to count the number of motor boats in marine protected areas, the data will be used by IMEC to train their machine learning algorithms.

NOTE: this repository needs to be cloned or unzipped in /home/pi/Amilcar

Hardware requirements

• 3 Raspberry Pi 5 for better time precision
• 3 Adafuit ultimate GPS HAT with CRC1220 small battery
• 3 GPS antennas for better time accuracy, use the same GPS antenna for better accurancy
• 3 Hydrophone
• 3 ADC/DAC pro
• 3 power banks
• 3 rPi5 cooling fans

We are using GPS to set the internal time of the rPi, and using Raspberry Pi 5 RTC as fallback in case we lose GPS fix.

The RTC is disciplined by GPS every second. We are using JACK for real time recording with a python script check ./audio for more details on the recording

We will also have a Raspberry Pi to locate the boat every second, check ./localization for more details on the configuration

Some considerations:

• We use rPi 5 for its better time accuracy, rPi5 requires 5V/5A or 5v/3A while reducing USB current so we chose 5V/3A power banks.
• Recording in real-time and getting GPS time, consumes lots of CPU power, the rPi gets very hot (up to 83 degrees) and as it throttles at 80 degress, it can shutdown on its own so better use a cooling fan!
• Sometimes we get an IO error and everything blocks because of the load on the rPi, if you want a system that will stay all the time in the sea, look for other options than the rPi as it already requires many tweaking to record in real time, -There will always be some jitter, meaning imperfect synchronization between the recordings from different Raspberry Pis (in our case, up to 18 ms). This jitter cannot be corrected in software, it must be addressed through hardware-level synchronization.
• We use WAV format for audio which can be heavy (1.2 GO an hour) so use a large SD Card, we chose WAV because we can inject in it directly the timestamps as cue points

Configuring AMILCAR

Step 1: Flash Operating System to the micro-SD card

Depending on your computer operating system, the installation procedure can change. Please follow the instruction on the Raspbian website: https://www.raspberrypi.com/software/

From the link above download and install the Raspberry Pi Imager.

In the Raspberry Pi Imager select:

• Device - Raspberry Pi 5,
• Operating System - Raspberry Pi OS (64-BIT)
• Storage - micro-SD card 256 GO minimum

After flashing, insert the micro-SD into the Raspberry Pi. Power ON the Raspberry and connect it to a screen with an HDMI cable, and connect a mouse and a keyboard.

On the first boot of the OS you need to fill in the location and language info, username and password.

For the username type: pi For the password type: raspberry

Step 2: Enable SSH using Ethernet cable

• Check the name of ethernet interface using:

nmcli device status

then run the following command to be able to SSH from your computer to the rPi using an ethernet cable

sudo nmcli con mod "name of ethernet interface" ipv4.addresses 192.168.50.2/24 ipv4.gateway 192.168.50.1 ipv4.dns 8.8.8.8 ipv4.method manual

better use different IP address for each rPi

Step 3: Download Amilcar and install real time kernel

From your Raspberry Pi download the latest Release or clone the repository of Amilcar here: [https://github.com/nermine11/Amilcar] This repository needs to be cloned or unzipped in /home/pi/Amilcar

Unzip the content of the release in the /home/pi/Amilcar folder We are going to record in real time so we to be able to do that, we will install a real time kernel instead of rPi kernel which is best-effort, the difference is a real time kernel will give absolute priority to our recording while best-effort can have milliseconds of latency and allocate time instead for other services go to ./install_real_time_kernel_for_linux and follow the instructions in the readme

Step 4: install Amilcar

In install_amilcar script, we create system services and run the scripts for GPS, RTC, and reduce latency as explained below, We reduce latency by running a RT kernel (real-time) by disabling many services, and running headles rPi, check reduce_latency scripts for more details The service descriptions below are not up to date check install_amilcar.sh instead

run the following commands: make the file executable

sudo chmod +x install_amilcar.sh

Run

source install_amilcar.sh

And that's it now the GPS, RTC are set and the rPi will start recording, for more details on what install_amilcar script contains see below, Note: you only run install_amilcar.sh, what's below is only an explanation that is not the most up-to-date,

• Set the internal time of the rPi as GPS time

Run GPS_setup.sh

sudo chmod +x GPS/GPS_setup.sh
./GPS/GPS_setup.sh

Comment manually to not use Interent time servers the content of

• #debian vendor zone

• #use time sources from dhcp

• #use ntp sources found in /etc/chrony/chrony.conf

• check ./GPS to see how to choose the offsett

Step ': Discipline the RTC using GPS and use RTC as fallback

Make the file RTC_GPS_sync.sh executable

sudo chmod +x ./GPS/RTC_GPS_sync.sh

Create a systemd Service File

sudo nano /etc/systemd/system/rtc-gps-sync.service

Paste the following content:

[Unit]
Description=RTC fallback
After=gpsd.service
Wants=gpsd.service

[Service]
ExecStart=/home/pi/Amilcar/GPS/RTC_GPS_sync.sh
Restart=always
RestartSec=1

[Install]
WantedBy=multi-user.target

save and exit

Reload the service files to include the new service.

sudo systemctl daemon-reload

Start and enable the service:

sudo systemctl start RTC_GPS_sync.service

And automatically get it to start on boot:

sudo systemctl enable RTC_GPS_sync.service

Reboot the Raspberry

sudo reboot

• Step 6: add audio group to user

sudo usermod -aG audio pi
sudo reboot

• Step 7: configure ADC+DAC converter Run setup_audip.sh

 sudo chmod +x audio/setup_audio.sh
./audio/setup_audio.sh

• Step 8: reduce latency

Make the file reduce_latency_on_boot.sh executable and run it

sudo chmod +x ./audio/reduce_latency_on_boot.sh
./audio/reduce_latency_on_boot.sh

Make the file reduce_latency.sh executable

sudo chmod +x ./audio/reduce_latency.sh

Create a systemd Service File

sudo nano /etc/systemd/system/reduce_latency.service

Paste the following content:

[Unit]
Description=reduce latency

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/home/pi/Amilcar/audio/reduce_latency.sh

[Install]
WantedBy=multi-user.target

save and exit

Reload the service files to include the new service.

sudo systemctl daemon-reload

Start and enable the service:

sudo systemctl start reduce_latency.service

And automatically get it to start on boot:

sudo systemctl enable reduce_latency.service

Reboot the Raspberry

sudo reboot

• Step 8: Increase audio volume

check /audio for more details

amixer -D hw: 0 cset name='ADC Capture Volume' 96,96
sudo alsactl store

• Step 9: run the jack server to record audio

Create a systemd Service File

sudo nano /etc/systemd/system/jack_server.service

Paste the following content:

[Unit]
Description=run jack server

[Service]
Restart=always
RestartSec=1
User=pi
Group=audio
ExecStart=/usr/bin/jackd -P70 -t 2000 -d alsa -d hw:0 -r 44100 -p2048 -n3

[Install]
WantedBy=multi-user.target

save and exit

Reload the service files to include the new service.

sudo systemctl daemon-reload

Start and enable the service:

sudo systemctl start jack_server.service

And automatically get it to start on boot:

sudo systemctl enable jack_server.service

Reboot the Raspberry

sudo reboot

• Step 10: record audio

Create a systemd Service File

sudo nano /etc/systemd/system/record_audio.service

Paste the following content:

[Unit]
Description=Hydrophone Audio Recorder
After=jack_server.service gpsd.service
Wants=jack_server.service gpsd.service

[Service]
ExecStart=/home/pi/Amilcar/venv/bin/python /home/pi/Amilcar/audio/record_audio.py
WorkingDirectory=/home/pi/Amilcar
Restart=always
RestartSec=1
User=pi
Group=audio

[Install]
WantedBy=multi-user.target

save and exit

Reload the service files to include the new service.

sudo systemctl daemon-reload

• Step 11: add a timer for record audio

We want to start recording after 10 minutes of reboot, so that the 3 rPis could start more or less at the same time, and to give some time for GPS fix, so we will use a .timer systemd unit file

Create a systemd Service File

sudo nano /etc/systemd/system/record_audio.timer

Paste the following content:

[Unit]
Description=timer for Hydrophone Audio Recorder

[Timer]
OnBootSec=10min
Unit=record_audio.service

[Install]
WantedBy=timers.target

save and exit

Reload the service files to include the new service.

sudo systemctl daemon-reload

**Disable record_audio.service so it don't start on boot

sudo systemctl disable record_audio.service

Start and enable the service:

sudo systemctl start record_audio.timer

And automatically get it to start on boot:

sudo systemctl enable record_audio.timer

Reboot the Raspberry

sudo reboot

##Ressources: https://wiki.linuxaudio.org/wiki/raspberrypi : great discussion on running real time audio using Raspberry Pi and using JACK https://wiki.linuxaudio.org/wiki/system_configuration#do_i_really_need_a_real-time_kernel