Temperature and Humidity Monitor Using DHT11, OLED, RGB LED, and Buzzer

Arduino Uno Rev3

momentary push button

PAPERCUTTER

HW-479

DHT11 sensor

Active Buzzer

Arduino IDE

128x64 OLED display

<html><body>This is a simple and beginner-friendly Arduino project that reads temperature and humidity data from a DHT11 sensor, displays the readings on a 0.96" OLED display, and provides visual alerts using an RGB LED and audible alerts using a buzzer. It also includes two push buttons—one to toggle temperature units (Celsius ↔ Fahrenheit) and another to enable or disable the LED. Components Used: Arduino UNO DHT11 Temperature &amp; Humidity Sensor (x1) 0.96" I2C OLED Display (SSD1306-based) (x1) HW-479 RGB LED Module (x1) Push Buttons (x2) Buzzer (x1) Interfacing the DHT11 Sensor The DHT11 is a low-cost digital sensor for measuring temperature and humidity. It is easy to use with Arduino and outputs digital signals, requiring no analog-to-digital conversion. It has three pins: VCC, GND, and OUT. Connect VCC to 5V of Arduino. Connect GND to GND of Arduino. Connect OUT to any digital pin (e.g., pin 2). Note: The DHT11 offers decent performance for simple projects but is limited in both accuracy and range: Temperature accuracy: ±2°C and Humidity range: 20–80% with ±5% accuracy For more precise applications, DHT22 is recommended. It offers: Temperature range: –40°C to +80°C (±0.5°C) and Humidity range: 0–100% (±2–5%) Since my project doesn't demand very high precision, I chose the DHT11. Interfacing the OLED Display (SSD1306) I used a 0.96" 128x64 OLED display based on the SSD1306 driver, which communicates over I2C protocol. Connections (for I2C OLED): GND → Arduino GND VCC → Arduino 5V SCL → A5 SDA → A4 I2C communication on Arduino UNO is hardware-bound to pins A4 (SDA) and A5 (SCL) due to the ATmega328P microcontroller. These pins are internally connected to the I2C peripheral, and libraries like Wire.h are coded to use these pins only. Using other pins will not work unless you use software-based I2C (not recommended for this case). Note (VERY Important): When using OLED displays—especially with the Adafruit SSD1306 library—memory becomes a major concern on Arduino UNO: a) High SRAM Usage: Arduino UNO has only 2 KB of SRAM. The Adafruit SSD1306 library in 128x64 mode allocates 1024 bytes just for the display buffer—half the SRAM gone! This limits the remaining memory for logic, sensor data, and global variables. b) Sketch Size and Compilation Time: These libraries are large and take longer to compile. Though this doesn't affect performance, it can slow development on limited systems. c) Limited Room for Additional Features: In my case, using the Adafruit library caused the OLED to display nothing—this was due to memory overflow. Switching to the U8g2 library helped solve this. U8g2 uses paged rendering—it draws the screen in segments rather than buffering the entire display. This uses less SRAM and allowed me to add sensors and variables without issues. However, memory usage still needs monitoring, especially for global variables and large arrays. Interfacing HW-479 RGB LED The HW-479 RGB LED module has 4 pins: R (Red) G (Green) B (Blue) – (Common Cathode / GND) Connect the – pin to Arduino GND, and the R, G, and B pins to any PWM-enabled digital pins (e.g., pins 5, 6, and 9). Use PWM to mix colors and create alerts: Example: Below 8°C → Display icy blue Above 30°C → Display red This gives a quick visual feedback of environmental conditions. Adding Buzzer and Push Buttons Buzzer: Connect one terminal to GND, the other to digital pin 8. Push Buttons: Connect one terminal to GND, and the other to a digital input pin (e.g., pins 3 and 4). Make sure to use the non-shorted diagonal terminals on the button. Functions: Button 1 (Pin 3): Switch between Celsius and Fahrenheit. Button 2 (Pin 4): Toggle RGB LED ON/OFF. Potential Upgrades and Future Improvements Initially, I considered adding Bluetooth or ESP8266 to send data to a phone, but had to drop the idea due to memory limitations of the Uno when using OLED libraries. However, using an Arduino Mega or a more memory-efficient display, such upgrades become feasible: a) Add a Real-Time Clock (RTC) module to display date and time on OLED. b) Log readings to SD card or external EEPROM. c) Send data wirelessly to a smartphone via Bluetooth or ESP8266/ESP32. d) Plot data on a PC using SerialPlot or a Python visualization script. e) Build a web dashboard if ESP8266/ESP32 is used. This project is a great starting point for learning sensor interfacing, I2C communication, PWM color mixing, and memory optimization on microcontrollers like the Arduino UNO. <figure><img src="https://projects.arduinocontent.cc/2ffcadbb-82c3-4eb0-ab8f-acc2bacd2379.jpg"/><figcaption>Breadboard Integration</figcaption></figure> </body></html>

Temp Logger Code

Temperature Logger

Project Schematic

Temperature and Humidity Monitor Using DHT11, OLED, RGB LED, and Buzzer

A beginner-friendly Arduino project that monitors temperature and humidity using a DHT11 sensor, displays readings on an OLED, and provides real-time visual and audible alerts through an RGB LED and buzzer.