Central to the system's ability to operate autonomously when needed while preferring manual control when available is the heartbeat mechanism. This solution to the mode-switching problem has been introduced to enhance both reliability and usability.
The heartbeat mechanism governs mode selection between remote and autonomous operation. AR1 embeds an HB:1 field in each STAT frame transmitted over RS-485 approximately every two seconds; its absence for five minutes triggers autonomous mode on AR3. The operator can deliberately enter autonomous mode at any time via a dashboard switch that halts heartbeat transmission while MQTT remains fully connected, and can restore manual control by re-enabling it. If AR1 loses its MQTT connection for more than five minutes, heartbeat transmission ceases automatically, producing the same result. In either case the Autonomous Mode Status Panel in the Home Assistant remote dashboard panels, continues to report the current phase, mode, and relay states from AR3's telemetry, and full dashboard control is restored once the MQTT connection recovers.
AR3 categorises heartbeat health into three states: fresh (received within four seconds), warning (absent for 60 seconds — logged and flagged on the FireSys LCD), and failed (absent for 300 seconds — autonomous mode entered). Return to remote mode requires sustained heartbeat presence for 60 seconds, preventing oscillation if the link is unstable. On resuming heartbeat transmission AR1 implements a state adoption mechanism, capturing AR3's current telemetry and publishing it to MQTT before issuing any new commands, ensuring the dashboard reflects actual system state rather than values that were current when communications failed.
For more background and technical detail refer to Criteria for Automatic actions in the Autonomous mode, System response to Ember attack.
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