Auto Air Cooler Relay

Device Type
name: Auto Air Cooler Relay — problem: Manual air cooler switches require constant monitoring to turn the unit on and off based on room temperature. This device automates that process using a simple hysteresis thermostat, eliminating the need for manual intervention while maintaining energy efficiency.

Hardware
chip: ESP32-C3 — board: ESP32-C3-DevKitM-1 — gpios: gpio4: I2C SDA (AHT20 temperature sensor) — gpio5: I2C SCL (AHT20 temperature sensor) — gpio10: Relay control signal (SRD-05VDC) — peripherals: name: AHT20 Temperature/Humidity Sensor — type: I2C Sensor — bus: I2C (GPIO 4 & 5) — purpose: Measures ambient temperature for control logic · name: SRD-05VDC Relay — type: Electromagnetic Relay — pin: GPIO 10 — purpose: Switches the air cooler on/off based on temperature thresholds

Inputs
kind: Temperature sensor — label: AHT20 (I2C) — hardware: AHT20 Temperature/Humidity sensor connected via I2C — behavior: Continuously reads ambient temperature. Device samples reading to evaluate control logic.

Outputs
kind: Relay — label: Air Cooler Control — hardware: SRD-05VDC relay driven by GPIO 10 — behavior: Relay energizes when temperature exceeds 25°C (ON). Relay de-energizes when temperature drops below 22°C (OFF). In the 22-25°C band, relay maintains its current state (hysteresis).

Connectivity
stack: None — transport: Local only — purpose: Device operates autonomously with no Wi-Fi, cloud, or remote control capability. All logic executes locally on the ESP32-C3.

Business Logic
powerOnBehavior: On startup, the device initializes the AHT20 sensor and GPIO pin. It reads the current ambient temperature and immediately sets the relay state: ON if temperature > 25°C, OFF if temperature ≤ 25°C. After startup, the device continuously polls the temperature sensor and applies hysteresis logic. — dayToDayOperation: The device continuously monitors room temperature. When temperature crosses 25°C going upward, the relay activates (air cooler turns ON). The relay remains on until temperature falls below 22°C, at which point it deactivates (air cooler turns OFF). This 3°C deadband prevents rapid on/off cycling. There are no user controls, displays, or feedback indicators — the device runs silently in the background.

Failure Modes
scenario: AHT20 sensor fails or becomes unresponsive — behavior: Device will attempt to read sensor but will not receive valid data. Behavior depends on firmware error handling — typically the relay remains in its last known state or defaults to OFF for safety. A firmware watchdog or periodic retry could be implemented. · scenario: Relay fails to energize — behavior: Air cooler will not turn on even when temperature exceeds 25°C. This is a hardware failure outside firmware control. An external monitoring mechanism (manual check) is recommended. · scenario: Power loss and recovery — behavior: On power restoration, the device boots and immediately reads the current temperature, setting the relay state based on that reading. No state is persisted across power cycles — this is the intended behavior.