Smart Thermostat with ESP32-S3: An Information Theory Project

Last year, as part of my Information Theory and Coding course, I developed a smart thermostat using the ESP32-S3 microcontroller. This project was more than just a simple temperature controller; it was an exercise in integrating various communication protocols and a robust control logic into a single IoT device.

The Hardware Architecture

The system’s hardware is designed to simulate a real climate control environment:

Core: The ESP32-S3 provides the necessary processing power and dual-radio capabilities (WiFi and BLE).
Input: A 10k Potentiometer acts as an analog temperature sensor.
Visual Feedback: Status LEDs (Green, Red, Blue) and a 7-segment Display for local readout.

The temperature reading is performed by mapping the internal ADC values:

// Mapping analogRead (0-4095) to a range of -10 to 60 degrees
tempActual = ((((analogRead(pot)) * 70) / 4095) - 10);

System Logic: The State Machine

The behavior of the thermostat is governed by a finite state machine that incorporates hysteresis ($H$). This is a critical concept in control theory to prevent rapidly switching the relay on and off when the temperature is exactly at the set point.

stateDiagram-v2 S0_IDLE --> S1_COLD: t < tObj - H S1_COLD --> S0_IDLE: t >= tObj S0_IDLE --> S2_HOT: t > tObj + H S2_HOT --> S0_IDLE: t <= tObj state S0_IDLE { Green_LED } state S1_COLD { Red_LED Heating_Active } state S2_HOT { Blue_LED Cooling_Active }

In the code, this is implemented within the loop() function using a switch statement that manages the transitions between NEUTRAL, CALENTANDO (Heating), and ENFRIANDO (Cooling).

Communication Protocols

The ESP32-S3 handles two concurrent interfaces:

1. Bluetooth Low Energy (BLE)

I implemented a custom BLE server with a specific callback class to handle remote commands. This allows for low-power configuration via a mobile app or terminal.

class MyCallbacks: public BLECharacteristicCallbacks {
  void onWrite(BLECharacteristic* pCharacteristic) {
      String value = pCharacteristic->getValue().c_str();
      if (value.length() > 0) {
          int comando = value[0] - '0'; // Command ID
          switch (comando) {
              case ESTABLECER_TEMP_OBJETIVO:
                  tempTermo = value.substring(1).toFloat();
                  guardarEEPROM("tempTermo", tempTermo);
                  break;
              // ... other commands
          }
      }
  }
};

2. Integrated Web Dashboard

The device also acts as a WiFi Access Point hosting a responsive web server. This interface provides a more user-friendly way to monitor and control the system.

Thermostat Web UI

The UI is designed to be clean and intuitive, following a modern “Glassmorphism” aesthetic:

Real-time Monitoring: The current temperature is displayed prominently, fetching data from the /data JSON endpoint every 2 seconds.
Dynamic Controls: Users can adjust the target temperature and hysteresis with a 0.5°C precision using interactive buttons.
State Indicators: A color-coded status badge (“Heating”, “Cooling”, or “Optimal”) provides immediate context.

Non-Volatile Storage (Preferences)

To ensure the settings persist after a power cycle, I used the Preferences.h library, which interacts with the ESP32’s NVS flash partition.

void guardarEEPROM(const char* clave, float valor) {
    preferences.begin("TEMPERATURAS", false);
    preferences.putFloat(clave, valor);
    preferences.end();
}

Conclusion

This project successfully applied theoretical concepts of signal coding and data transmission in a practical IoT application. The combination of hardware control, wireless communication, and persistent storage makes this a robust prototype for smart home automation