The Problem

Most air conditioners still rely on infrared remote controls. They have no awareness of whether anyone is in the room, no ability to integrate with home automation, and no smart scheduling. The result is wasted energy from units running in empty rooms, and the classic problem of the AC shutting itself off at night because the user is asleep and "looks empty" to basic motion sensors.

The Solution

ThermaLink-C3** is a compact, low-cost smart controller that retrofits any IR-controlled air conditioner. Built around the ESP32-C3 SuperMini, it learns the remote codes of any AC, monitors temperature and presence, and decides intelligently when to turn the unit on, off, or hold.

How It Works

The system runs a closed control loop every ~30 seconds:

1. Sense — DHT22 reads ambient temperature; PIR module detects motion; BLE scan looks for known beacons (your phone, smartwatch).

2. Decide — Fuses all three signals to determine "occupied or not." If occupied and temperature exceeds setpoint, cool. If unoccupied, turn off.

3. Act — Transmits the appropriate learned IR code to the AC via the IR emitter.

Key Features

- IR learning mode: clones any AC remote — no need to know the protocol in advance.

- Sleep Mode: combines time windows + BLE beacon detection so the AC doesn't shut down when a sleeping user stops moving.

- Hysteresis-based control: prevents constant on/off cycling around the setpoint.

- Non-volatile storage: learned codes and setpoint persist across power cycles via NVS.

- Hardware debounce + pull-ups: control logic is robust without relying on software.

- USB-C powered: single cable for power and reprogramming.

Hardware Architecture

- MCU: ESP32-C3 (single-core RISC-V, WiFi + BLE 5)

- Temperature: DHT22 with on-module pull-up

- Presence: HC-SR501 PIR + BLE proximity scanning

- IR TX: KY-005 module (or discrete 940nm LED + BC337 NPN driver for extended range)

- IR RX: KY-022 (VS1838B) demodulator

- User input: 2 tactile buttons with RC hardware debounce

- Power: USB-C → onboard 3.3V LDO → bulk + decoupling caps

Design Notes

The ESP32-C3 SuperMini has a known weak ceramic antenna, so a 10mm keepout zone is enforced around it on both layers to protect WiFi/BLE range. The IR receiver uses a 100Ω + 4.7µF supply filter on its VS pin to suppress demodulator noise, as recommended by Vishay. The IR LED driver uses a low-side NPN to allow >100mA pulses from the 5V rail without overloading the GPIO.

Future Work

- MQTT integration for Home Assistant

- Web-based configuration UI hosted on the ESP32-C3

- Schedule editor with multiple sleep windows

- Power consumption estimation based on usage patterns

- 3D printed enclosure