Control application

The main control application of Aquarium control implements the following features:

• Data acquisition of water temperature, pH and conductivity
• Data acquisition of ambient temperature and humidity
• Refill control for fresh water
• Feed control
• Water temperature control using air ventilation and heater
• Balling mineral dosing

The control of the relays for operating the devices can use two different modes:

• Using an Arduino-based relay actuation
• Using the GPIO of the Raspberry Pi (requires additional hardware)

Additionally, the main control application implements the following supporting features:

• Version comparison between database and application
• Configuration using a Rust .toml configuration file
• Logging
• Command interface to receive instructions from outside of the application via a POSIX message queue
• Storage of recorded data in SQL database
• File-based communication to RAM-disk
• Usage of simulator to run with simulated sensor data for development purposes
• Schedule checks to limit the hour of day of operating certain actuators
• Communication with HW Watchdog

The application is written in Rust and is automatically started using systemd.

The documentation of the software is available here.

Development for the main control application requires the setup of the development environment.

There is a release procedure which is highly recommended to be followed also by anyone developing the SW further.

Architecture

Startup of the application

The startup uses a two-layer approach:

1. main() - Simple error handler wrapper that calls run() and exits with code 1 on errors
2. run() - The actual initialization orchestrator that performs the major steps

Phase 1: Command Line & Configuration

• Parses command line arguments ("help", "version", config file)
• Sets the default config file: /etc/aquarium_control/aquarium_control.toml
• Loads configuration and creates ExecutionConfig (boolean flags determining which modules to run)

Phase 2: System Setup

• Initializes the logging system
• Logs version information and executable hash
• Verifies root privileges (required for hardware access)
• Publishes process ID to file for client communication

Phase 3: Database & Hardware

• Connects to database (MariaDB)
• Creates component-specific SQL interfaces (Schedule, Balling, Refill, Heating, Feed, Data)
• Validates database schema and version compatibility
• Initializes hardware components if configured:

   - RGB LEDs, GPIO handlers
   - Tank level switches
   - I2C interfaces
   - Atlas Scientific sensors
   - DHT temperature/humidity sensors

Phase 4: Communication Channels

• Creates the Channels struct containing ~30+ inter-thread communication channels
• Uses custom AquaSender/AquaReceiver wrappers for MPSC channels
• Establishes bidirectional and unidirectional message paths between all modules

Phase 5: Component Initialization

• Instantiates all system components:

   - Data loggers, sensor managers, relay managers
   - Food injection, mineral dosing (balling), water injection/refill
   - Heating/ventilation control
   - Monitors, watchdog, schedule checker
   - IPC messaging system (Linux)

Phase 6: Thread Spawning

• Uses std::thread::scope for guaranteed cleanup
• Spawns threads conditionally based on ExecutionConfig flags
• Critical: A 3-second startup delay allows sensors to acquire first data before control loops activate

Architecture of thread configuration

• The Channels module (src/launch/channels.rs) acts as a central wiring diagram, with the Signal Handler serving as the main event coordinator.
• The ExecutionConfig decouples configuration from execution - threads only receive flags about which modules are active, not the full config - this also avoids ownership issues.

Threads

The application spawns the following threads:

Overview of threads

Thread name	Purpose
signal_handler	Receiving signals from the operating system
schedule_check	Polling the database to capture changes of the actuator channel. Informing other threads about it.
sensor_manager	Data acquisition
relay_manager	Actuation of relays
data_logger	Recording of data
tank_level_switch	Postprocessing of tank level switch position signal
refill	Fresh water refill control
heating	Heating control
ventilation	Ventilation control
balling	Balling mineral dosing control
watchdog	Sending alive signal to Raspberry Pi hardware watchdog
monitors	Diagnostics (not implemented as of January, 2026)
messaging	Receiving communication via message queue
memory	Monitoring memory utilization
ds18b20	Recording data from DS18B20 temperature sensor
feed	Feed control
i2c_interface	Communication via I2C
atlas_scientific	Recording data from Atlas Scientific temperature sensor
dht	Recording data from DHT sensor
publish_pid	Writing PID to lock file