FrostByte - ESP-01S Temperature-Controlled Relay with M2302 (DHT22)

This project uses an ESP-01S Wi-Fi module together with an M2302 (DHT22) temperature and humidity sensor to control a relay. The relay switches ON or OFF based on the average temperature over the last 300 seconds, using hysteresis to avoid rapid toggling.

🔧 Hardware Components

• ESP-01S Module (ESP8266)
• M2302 (DHT22) temperature & humidity sensor
• ESP-01S 1-Channel Relay Module, also called ESP-01S / ESP01S Relay Daughter Board. It has two screw terminals and a 2x4 pin-header compatible with ESP-01S Module.
• 5V power supply for the relay module, also powering the sensor and ESP-01
• Wires

⚙️ Functionality

• Takes one temperature reading every 10 seconds.
• Stores the latest 30 readings (≈ 5 minutes).
• Calculates the average temperature from the buffer.
• Relay turns ON when average temperature > 5.0°C.
• Relay turns OFF when average temperature < 3.0°C.
• No switching occurs between 5.0°C and 7.0°C (hysteresis zone).

🌐 Wi-Fi Access Point + Web Interface

The ESP-01S can act as its own Wi-Fi access point (AP) so you can connect to it directly (without an internet router) and monitor the temperature in a web browser.

• The ESP-01S starts in AP mode with a name FrostByte and password fridgelord. These can be changed in the code.
• You can connect to it from your phone or computer via Wi-Fi.
• After connecting, open a browser and go to http://192.168.4.1
• The ESP will serve a simple HTML page showing the current average temperature and relay state.

📦 PlatformIO Configuration (platformio.ini)

[env:esp01_1m]
[env:esp01_1m]
platform = espressif8266
board = esp01_1m
framework = arduino
monitor_speed = 9600
lib_compat_mode = strict
lib_ldf_mode = chain
lib_deps =
  ESP32Async/ESPAsyncTCP
  ESP32Async/ESPAsyncWebServer
upload_port = COM3

Information on how to program an ESP-01S is available somewhere else. It is configured to have the programmer at port COM3.

Using the more stable **myDHT(()) library to support the DHT22 on Arduino available at https://github.com/tonimatutinovic/myDHT as a Git Submodule.

🔌 Wiring & Connections

Below are the required connections to set up the ESP-01S with the M2302 (DHT22) sensor and the ESP-01S relay module.

🧩 ESP-01S to M2302 (DHT22)

You need to solder these directly on the ESP-01S relay module, as you slot the ESP-01S in the 8-pin connector of the ESP-01S relay module. Or splice three wires while you connect the ESP-01S and ESP-01S relay module with 8 wires.

M2302 Pin	Connects To (ESP-01)	Notes
VCC	3.3V
GND	GND	Common ground
DATA	GPIO2

⚡ ESP-01S Relay Module

You need to power it with 5V, and use the relay contacts to control/switch the fridge compressor. WARNING: High voltage!

🪛 Power Supply Notes

• ESP-01S: Requires a regulated 3.3V power supply, that is already included in the ESP-01S relay module, which requires 5V.
• Relay module: Needs 5V to power the relay coil. That is supplied in to the ESP-01S relay module.
• M2302 (DHT22): Runs at 3.3V, not 5V.
• Do not power the ESP-01S directly from USB or unregulated 5V.