Smart Environment Monitor — DESHBOT SHIEL+DHT22 + OLED + Bluetooth

by devkrishnavhora in Workshop > Science

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Smart Environment Monitor — DESHBOT SHIEL+DHT22 + OLED + Bluetooth

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To design a temperature and humidity monitoring system using an Arduino Nano, DHT22 sensor, OLED display, and Bluetooth module. The system measures the surrounding temperature and humidity, di

Supplies

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oled.jpeg

S.No.ComponentQuantity

1.Arduino Nano


2.DESHBOT Shield


3.DHT22 Temperature & Humidity Sensor


4.OLED Display


5.Bluetooth Module


6.Jumper Wires



7.USB/Battery Supply


CONNECTION

Pin Connections

DHT22

DHT22 PinArduino Nano

VCC-5V

DATA-D3

GND-GND

OLED Display

The OLED uses the Arduino Nano's I²C communication pins.

OLED PinArduino Nano

VCC-5V

GND-GND

SDA-A4

SCL-A5

Bluetooth Module

Bluetooth PinArduino Nano

TX-D0 (RX)

RX-D1 (TX)

STATE-D2

VCC-5V

GND-GND

Working Principle

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The DHT22 sensor measures the surrounding temperature and relative humidity.

The Arduino Nano reads these values and displays them on the 128×64 OLED display.

The Bluetooth module is used to communicate with a mobile phone. The STATE pin of the Bluetooth module is connected to D2 so that the Arduino can determine whether a Bluetooth connection is active.

When Bluetooth is connected, the Arduino also sends the temperature and humidity readings through Bluetooth.

System Flow

DHT22 Sensor
↓
Arduino Nano
↓
┌───────────────┐
↓ ↓
OLED Bluetooth
Display ↓
↓ Mobile
Temperature
Humidity
BT Status


Code Explanation – Step by Step


Step 1: Include Required Libraries


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

These libraries provide the functions required to control the OLED, communicate using I²C, and read the DHT22 sensor.

  1. Wire.h → I²C communication
  2. Adafruit_GFX.h → graphics and text functions
  3. Adafruit_SSD1306.h → OLED control
  4. DHT.h → DHT22 sensor control

Step 2: Define OLED Display


#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

The OLED display has a resolution of 128 × 64 pixels.

The Wire library is used for I²C communication.

Step 3: Define DHT22


#define DHT_PIN 3
#define DHT_TYPE DHT22

DHT dht(DHT_PIN, DHT_TYPE);

The DHT22 data pin is connected to D3.

The program specifies that the sensor being used is a DHT22.

Step 4: Define Bluetooth STATE Pin


#define BT_STATE 2

The Bluetooth module's STATE pin is connected to D2.

This pin is used to determine whether the Bluetooth device is connected.

Step 5: Start the System


void setup() {

The setup() function runs once when the Arduino is powered on.

Step 6: Start Bluetooth Communication


Serial.begin(9600);

The Arduino's hardware serial communication is started at 9600 baud.

The Bluetooth module is connected to:

D0 → RX
D1 → TX

Step 7: Configure Bluetooth STATE


pinMode(BT_STATE, INPUT);

The STATE pin is configured as an input so that the Arduino can read its status.

Step 8: Start the DHT22 Sensor


dht.begin();

This initializes the DHT22 sensor and prepares it for taking measurements.

Step 9: Start the OLED


if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
while (1);
}

This initializes the OLED using the I²C address 0x3C.

If the OLED is not detected, the Arduino stops at this point.

Step 10: Display Starting Message


display.setCursor(20, 10);
display.println("DHT22 SYSTEM");

display.setCursor(20, 30);
display.println("Starting...");

When the system starts, the OLED displays:

DHT22 SYSTEM

Starting...

Main Program

Step 11: Read Bluetooth Status


int btStatus = digitalRead(BT_STATE);

The Arduino reads the Bluetooth STATE pin.

If the pin is HIGH, the program considers Bluetooth to be connected.

If the pin is LOW, it displays that Bluetooth is not connected.

Step 12: Read Temperature


float temperature = dht.readTemperature();

The DHT22 measures the surrounding temperature and stores the value in the temperature variable.

The temperature is displayed in degrees Celsius (°C).

Step 13: Read Humidity


float humidity = dht.readHumidity();

The DHT22 measures relative humidity and stores the value in the humidity variable.

The value is displayed as a percentage (%).

Step 14: Display Bluetooth Status


display.print("BT: ");

if (btStatus == HIGH) {
display.println("CONNECTED");
}
else {
display.println("NOT CONNECTED");
}

The OLED displays either:

BT: CONNECTED

or:

BT: NOT CONNECTED

Step 15: Display Temperature


display.print("Temp: ");

if (isnan(temperature)) {
display.println("Error");
}
else {
display.print(temperature, 1);
display.println(" C");
}

The temperature is displayed with one decimal place.

Example:

Temp: 28.5 C

If the DHT22 fails to provide a valid reading, the OLED displays:

Temp: Error

Step 16: Display Humidity


display.print("Humidity: ");

if (isnan(humidity)) {
display.println("Error");
}
else {
display.print(humidity, 1);
display.println(" %");
}

The humidity is displayed with one decimal place.

Example:

Humidity: 62.3 %

Step 17: Send Data Through Bluetooth


if (btStatus == HIGH) {

Serial.println("===== DHT22 DATA =====");

Serial.print("Temperature: ");
Serial.print(temperature);
Serial.println(" C");

Serial.print("Humidity: ");
Serial.print(humidity);
Serial.println(" %");

Serial.println("======================");
}

When Bluetooth is connected, the Arduino sends the sensor readings to the connected mobile device.

Example Bluetooth output:

===== DHT22 DATA =====
Temperature: 28.5 C
Humidity: 62.3 %
======================

Step 18: Delay


delay(2000);

The Arduino waits for 2 seconds before taking another reading.

This prevents the DHT22 from being read too frequently and makes the display easier to read.

OLED Output

When Bluetooth is connected:

BT: CONNECTED

Temp: 28.5 C
Humidity: 62.3 %

When Bluetooth is disconnected:

BT: NOT CONNECTED

Temp: 28.5 C
Humidity: 62.3 %


Downloads

bluetooth_dht.ino

Conclusion


The DHT22 Temperature and Humidity Monitoring System successfully measures environmental temperature and humidity using the DHT22 sensor. The Arduino Nano processes the sensor readings and displays them on the OLED display. The Bluetooth module provides wireless communication with a mobile device, while the Bluetooth STATE pin allows the system to display the connection status. This project demonstrates basic environmental monitoring, OLED display control, and wireless data transmission using Arduino.