 |
The system employs four distinct communication protocols, each selected specifically for its role in the overall architecture. Understanding why each protocol was chosen and how they work together reveals much about the sophistication of the design.
MQTT, running between Module 1 and Module 2, provides the interface between Home Assistant and Arduino AR1. This protocol's publish-subscribe model with retained messages and quality-of-service guarantees makes it ideal for dashboard control, where state persistence across disconnections and guaranteed delivery of critical commands are essential. The MQTT broker running in a Docker container in the Raspberry Pi maintains the authoritative state of all controllable elements, ensuring that reconnecting clients immediately receive current system status. Topics are organized hierarchically, with pump control under home/pump/inTopic, peripheral states under home/peripheral1/set through home/peripheral4/set, and sensor readings published to home/sensor/ topics. This organization allows Home Assistant automations to subscribe to specific state changes and respond accordingly.
RS-485, linking Module 2 and Module 4 over the multicore cable, was chosen for its exceptional noise immunity and reliability over extended cable runs. The differential signaling inherent to RS-485 makes it highly resistant to electromagnetic interference from the diesel pump motor and electrical noise in the pump shed environment. The implementation uses framed messages with checksum protection and explicit acknowledgment of critical commands. Every frame follows the format <PAYLOAD|CHECKSUM> where the checksum is calculated as an XOR of all payload bytes, converted to two-character hexadecimal representation. Pump commands additionally include sequence numbers from 0 to 15 that roll over, allowing the receiving end to detect and acknowledge each unique command while ignoring duplicates that might result from retry logic.
The RS-485 protocol defines several message types, each serving specific purposes. Command frames beginning with CMD: contain pump and peripheral relay states along with a sequence number and LOCK status. Status frames beginning with STAT: provide relay mirror states, heartbeat status, and Home Assistant automation flags without commanding pump state changes. Configuration frames beginning with CFG: transmit manual intermittent timing parameters from Home Assistant to AR3. Heartbeat frames consist simply of HB:0 or HB:1 indicating whether manual control is active. Telemetry frames flow from AR3 to AR1, containing all sensor readings, current relay states, autonomous mode and phase information, and system ready status.
UDP broadcast, operating within Module 4 between AR2 and AR3, provides high-frequency sensor data delivery at 10 hertz. Arduino AR2 operates as a WiFi access point with SSID "Arduino2_AP", creating a dedicated wireless network for this critical sensor link. AR3 connects as a client and receives broadcast packets containing pipe-delimited key-value pairs of all sensor readings. A typical UDP packet might contain: EXT_TEMP:35.20|INT_TEMP:30.15|WATER_LEVEL:2.85|FLOW_OUT:165.30|BAT:13.20|OIL_OK:1|WATER_PV:0.15. The choice of UDP rather than TCP reflects the real-time nature of sensor data—if a packet is lost, the next reading will arrive in 100 milliseconds, making retransmission unnecessary and avoiding the latency that TCP's guaranteed delivery would introduce. The broadcast nature of UDP also means that multiple devices could listen to the sensor stream if future expansion requires it.
SMS communication to Module 5 provides the ultimate backup control path, operating entirely independently of the local network infrastructure. If both the NBN and local network fail, operators can still command the pump via the mobile network, ensuring that manual control remains possible under the most adverse conditions. This path is intentionally kept simple—a text message with a specific format sent to the pump controller's phone number can force pump activation or deactivation, bypassing all other control logic.
Autonomous control As described later, if all external communication is lost the system continues to operate using inputs from AR2 and control decisions from AR3 in Module 3 transmitted by cable to the Relay Module (AR2).
<< Electronic Modules | | The Heartbeat System and Mode Transitions >> |Table of Contents>