A DIY HVAC thermostat with ESP32 gives you WiFi-connected, app-controlled temperature regulation for your home or office AC and heating systems. Unlike basic thermostats, an ESP32-based controller offers remote access, scheduling, temperature logging, and smart integration — all for under ₹1,000 in components.
Why Build a Smart Thermostat?
Commercial smart thermostats (Nest, Ecobee) cost ₹15,000-25,000 and may not work well with Indian AC systems (split ACs, coolers, desert coolers). Building your own gives you:
- Full compatibility with any AC or heating system
- WiFi control from anywhere via Blynk, Home Assistant, or custom web interface
- Temperature logging and trend analysis
- Multiple zone support (different rooms)
- Integration with other smart home devices
- Total cost under ₹1,000
ESP32 as the Controller
The ESP32 is ideal for a smart thermostat:
- Built-in WiFi and Bluetooth for connectivity
- Multiple GPIO pins for sensors and relays
- Enough processing power for PID control and web server
- Deep sleep mode for battery-operated versions
- OTA (Over-The-Air) firmware updates
- Cost: ₹329 on Zbotic
Temperature and Humidity Sensing
Use DHT22 for combined temperature and humidity measurement. Mount the sensor away from direct AC airflow — in the centre of the room at 1.5m height for accurate ambient readings.
For multi-zone control, place a DHT22 in each room and connect them to the same ESP32 (or use ESP-NOW for wireless sensor nodes).
Temperature Sensors
Relay Output for HVAC Control
For split AC control: Most Indian split ACs use an IR remote. The ESP32 can send IR commands using an IR LED, eliminating the need for a relay. Libraries like IRremoteESP8266 support all major AC brands (Daikin, LG, Samsung, Voltas, Blue Star).
For direct relay control: For coolers, heaters, and older AC units, use a relay module to switch the power. Connect the relay to the AC unit’s power or control circuit.
For AC dry contact: Some central HVAC systems accept a thermostat dry contact (relay closure = call for cooling). Connect the relay as a dry contact to the HVAC control board.
WiFi Interface and App Control
ESP32 can run a web server directly, serve a simple HTML interface, and accept commands via HTTP or MQTT. Options:
- Blynk: Easy app interface with virtual pins. Free tier sufficient for a thermostat.
- Home Assistant: Full smart home integration. ESP32 communicates via MQTT.
- Custom web interface: ESP32 serves a responsive HTML page accessible from any browser on the same network.
- Telegram bot: Send commands and receive temperature alerts via Telegram — works from anywhere without port forwarding.
PID Temperature Control Algorithm
For stable temperature control, implement PID (Proportional-Integral-Derivative) logic. For AC on/off control (you cannot modulate AC compressor speed), PID determines the duty cycle — how long the AC runs vs rests in each cycle. This prevents overshooting and oscillation.
Simpler alternative: bang-bang control with hysteresis. AC on above 26°C, off below 24°C (2°C hysteresis). This works well for most home applications where ±1°C accuracy is acceptable.
Recommended Components
Smart Thermostat Components
Installation and Safety
- Mount the sensor away from AC vents, windows, and direct sunlight
- Enclose mains relay wiring in a proper junction box
- Use ISI-marked wire for any mains connections
- Test thoroughly before leaving unattended
- Add a physical override switch in case WiFi or ESP32 fails
Frequently Asked Questions
Can I build a smart thermostat for my split AC?
Yes. Use an ESP32 with an IR LED to send on/off/temperature commands to the AC via infrared — the same way your remote works. No relay needed for split ACs. Cost under ₹500.
Is an ESP32 thermostat reliable enough for daily use?
With proper code (watchdog timer, error handling, fallback to manual mode), ESP32 thermostats are very reliable. Add a physical override switch for safety during firmware updates or WiFi outages.
What accuracy can I expect?
DHT22 provides ±0.5°C accuracy. Combined with 1-2°C hysteresis in the control loop, room temperature stays within ±1-2°C of the set point — comparable to commercial smart thermostats.
Can I control multiple AC units with one ESP32?
Yes. An ESP32 has enough GPIO pins for multiple IR LEDs (one per AC unit) and multiple temperature sensors. Each zone can have independent setpoints and schedules.
Where can I buy ESP32 and sensors in India?
Zbotic.in stocks ESP32 development boards (₹329), DHT22 sensors (₹91), and relay modules (₹84). Complete thermostat project cost is under ₹1,000.
Shop Cooling & Thermal Components at Zbotic
India’s trusted store for electronics components. Fast shipping, genuine products, and expert support.
Add comment