SonarSimulator

NMEA-0183 depth simulator for serial-connected systems.

Features

• Generates SDDPT or SDDBT frames once per second by default.
• Uses a deterministic depth pattern based on current second (10 + second).
• Sends data over a serial port (/dev/ttyUSB0 and 9600 by default).
• Can run manually or as a systemd service (nmea.service).

Repository Layout

• Script/sonar_simulator.py: simulator entrypoint.
• Script/autolaunch.sh: launcher used by systemd.
• Script/sonar_simulator_unittest.py: unit tests.
• Script/unittest.sh: test runner.
• Install/install.sh: service installation script.
• BOM.txt: hardware bill of materials.

Requirements

• Ubuntu (tested workflow targets Raspberry Pi with Ubuntu Server).
• Python 3.
• pyserial (python3-serial package).

Manual Run

From repository root:

python3 Script/sonar_simulator.py /dev/ttyUSB0 9600

Optional arguments:

python3 Script/sonar_simulator.py /dev/ttyUSB0 9600 --sentence-type dbt --interval 0.5 --iterations 10

Install as Service

From repository root:

bash Install/install.sh

This installs and starts nmea.service with default environment values:

• SONAR_SERIAL_PORT=/dev/ttyUSB0
• SONAR_BAUD_RATE=9600
• SONAR_SENTENCE_TYPE=dpt

Service commands:

sudo systemctl status nmea
sudo systemctl restart nmea
sudo systemctl stop nmea

Change Serial Port, Baud Rate, or Sentence Type

Option 1 (recommended): override service environment values in the unit file.

sudo systemctl edit --full nmea
# Update SONAR_SERIAL_PORT, SONAR_BAUD_RATE, and SONAR_SENTENCE_TYPE (dpt or dbt)
sudo systemctl daemon-reload
sudo systemctl restart nmea

Option 2: export environment values before running manually.

SONAR_SERIAL_PORT=/dev/ttyUSB1 SONAR_BAUD_RATE=115200 SONAR_SENTENCE_TYPE=dbt bash Script/autolaunch.sh

Run Tests

From repository root:

bash Script/unittest.sh

Notes

• The simulator writes one frame per cycle terminated by \r\n.
• If serial opening fails, the script logs the error and exits cleanly.