Project Documentation

Arduino Nano-Based Bluetooth Temperature and Humidity Monitor with OLED Display and Alert Buzzer

Circuit Documentation

Summary

The circuit in question is designed to monitor temperature and humidity using an AHT10 sensor, display the readings on a 128x64 OLED display, and provide a visual alert through a buzzer if the temperature exceeds a predefined threshold. The circuit is controlled by an Arduino Nano microcontroller, which also handles Bluetooth communication through an HC-05 Bluetooth module. The circuit includes resistors for current limiting and pull-up purposes.

Component List

Arduino Nano

Microcontroller board based on the ATmega328P
It has a variety of digital and analog I/O pins and supports serial communication.

Buzzer

An electromechanical component that produces sound when energized.
Typically used for audible alerts or alarms.

128x64 OLED Display (I2C IIC SPI Serial)

A small graphical display with organic light-emitting diodes.
Communicates with the microcontroller via I2C protocol.

Resistor (100 Ohms)

A passive two-terminal electrical component that implements electrical resistance as a circuit element.
Used for current limiting or voltage dropping.

Resistor (2000 Ohms)

Another resistor with a higher resistance value.
It may be used for pull-up purposes or to limit current to a safe level for other components.

HC-05 Bluetooth Module

A wireless communication module that allows for Bluetooth connectivity.
It can be used to send and receive data between the Arduino and a Bluetooth-enabled device.

AHT10

A high-precision temperature and humidity sensor.
Provides digital output and communicates over the I2C bus.

Wiring Details

Arduino Nano

D1/TX connected to a 2000 Ohm resistor.
D0/RX connected to TXD on the HC-05 Bluetooth Module.
D9 connected to one end of a 100 Ohm resistor, the other end connected to the buzzer.
GND connected to the ground pins of all other components.
5V supplies power to the VCC pins of the HC-05 Bluetooth Module, AHT10, and OLED Display.
A5 connected to the SCL pins of the AHT10 and OLED Display for I2C clock.
A4 connected to the SDA pins of the AHT10 and OLED Display for I2C data.

Buzzer

PIN connected to the other end of the 100 Ohm resistor.
GND connected to the common ground.

128x64 OLED Display (I2C IIC SPI Serial)

GND connected to the common ground.
SDA connected to A4 on the Arduino Nano for I2C data.
SCL connected to A5 on the Arduino Nano for I2C clock.
VCC connected to the 5V supply from the Arduino Nano.

Resistor (100 Ohms)

One end connected to D9 on the Arduino Nano.
The other end connected to the PIN of the buzzer.

Resistor (2000 Ohms)

One end connected to D1/TX on the Arduino Nano.
The other end connected to RXD on the HC-05 Bluetooth Module.

HC-05 Bluetooth Module

Key not connected in this configuration.
VCC connected to the 5V supply from the Arduino Nano.
TXD connected to D0/RX on the Arduino Nano.
RXD connected to the other end of the 2000 Ohm resistor.
State not connected in this configuration.
GND connected to the common ground.

AHT10

SDA connected to A4 on the Arduino Nano for I2C data.
SCL connected to A5 on the Arduino Nano for I2C clock.
GND connected to the common ground.
VIN connected to the 5V supply from the Arduino Nano.

Documented Code

The code for the Arduino Nano is written in C++ and is intended to be compiled and uploaded using the Arduino IDE. The code is responsible for initializing the AHT10 sensor and OLED display, reading temperature and humidity values, displaying these values on the OLED, and controlling the buzzer based on the temperature threshold. Additionally, it handles serial communication to send sensor readings over Bluetooth.

#include <Wire.h>
#include <AHTxx.h>
#include <Adafruit_SSD1306.h>
#include <Adafruit_GFX.h>

#define OLED_WIDTH 128
#define OLED_HEIGHT 64
#define OLED_ADDR 0x3C
#define BUZZER_PIN 9  // Define the pin for the buzzer
#define TEMP_THRESHOLD 36.0  // Temperature threshold for buzzer

Adafruit_SSD1306 display(OLED_WIDTH, OLED_HEIGHT);
float ahtValue;  // to store T/RH result
AHTxx aht10(AHTXX_ADDRESS_X38, AHT1x_SENSOR);  // sensor address, sensor type

void setup() {
  Serial.begin(115200);  // Serial communication for Bluetooth
  display.begin(SSD1306_SWITCHCAPVCC, OLED_ADDR);
  display.clearDisplay();

  while (aht10.begin() != true) {
    Serial.println(F("AHT1x not connected or fail to load calibration coefficient"));
    delay(5000);
  }

  Serial.println(F("AHT10 OK"));

  pinMode(BUZZER_PIN, OUTPUT); // Set buzzer pin as output
  digitalWrite(BUZZER_PIN, LOW); // Ensure buzzer is off initially
}

void loop() {
  // Read temperature
  ahtValue = aht10.readTemperature();
  display.clearDisplay();
  display.setTextSize(2);
  display.setTextColor(WHITE);
  display.setCursor(30, 0);
  display.println(F("Temp-"));

  if (ahtValue != AHTXX_ERROR) {
    display.setTextSize(2);
    display.setTextColor(WHITE);
    display.setCursor(35, 25);
    display.println(ahtValue);
    display.display();

    // Check if temperature exceeds the threshold of 36°C and control buzzer
    if (ahtValue > TEMP_THRESHOLD) {
      digitalWrite(BUZZER_PIN, HIGH); // Turn on buzzer
    } else {
      digitalWrite(BUZZER_PIN, LOW);  // Turn off buzzer
    }

    // Send temperature over Bluetooth
    Serial.print("Temperature: ");
    Serial.print(ahtValue);
    Serial.println(" C");
  } else {
    printStatus();
    digitalWrite(BUZZER_PIN, LOW); // Turn off buzzer if error occurs
  }

  delay(2000);  // Delay between temperature readings

  // Read humidity
  ahtValue = aht10.readHumidity();
  display.clearDisplay();
  display.setTextSize(2);
  display.setTextColor(WHITE);
  display.setCursor(30, 0);
  display.println(F("Humd-"));

  if (ahtValue != AHTXX_ERROR) {
    display.setTextSize(2);
    display.setTextColor(WHITE);
    display.setCursor(35, 25);
    display.println(ahtValue);
    display.display();

    // Send humidity over Bluetooth
    Serial.print("Humidity: ");
    Serial.print(ahtValue);
    Serial.println(" %");
  } else {
    printStatus();
  }

  delay(2000);  // Delay between humidity readings
}

void printStatus() {
  switch (aht10.getStatus()) {
    case AHTXX_NO_ERROR:
      Serial.println(F("No error"));
      break;
    case AHTXX_BUSY_ERROR:
      Serial.println(F("Sensor busy, increase polling time"));
      break;
    case AHTXX_ACK_ERROR:
      Serial.println(F("Sensor didn't return ACK, check connection"));
      break;
    case AHTXX_DATA_ERROR:
      Serial.println(F("Received data smaller than expected, check connection"));
      break;
    case AHTXX_CRC8_ERROR:
      Serial.println(F("CRC8 error, data may be corrupt"));
      break;
    default:
      Serial.println(F("Unknown status"));
      break;
  }
}

This code includes libraries for the AHTxx sensor and the Adafruit SSD1306 OLED display, defines constants for the display size and I2C address, and sets up the necessary pins and thresholds. The setup() function initializes the serial communication, display, and sensor, while the loop() function continuously reads the sensor data, updates the display, and checks the temperature against the threshold to control the buzzer. It also includes a printStatus() function to output sensor status messages to the serial monitor.