Bluetooth

 

Bluetooth

• Bluetooth is a standardized protocol for sending and receiving data via a 2.4GHz wireless link. 

• It’s a secure protocol, and it’s perfect for short-range, low-power, low-cost, wireless transmissions between electronic devices.

• These days it feels like everything is wireless, and Bluetooth is a big part of that wireless revolution.

•  You’ll find Bluetooth embedded into a great variety of consumer products, like headsets, video game controllers.

• In our world of embedded electronics hackery, Bluetooth serves as an excellent protocol for wirelessly transmitting relatively small amounts of data over a short range (<100m).

•  It’s perfectly suited as a wireless replacement for serial communication interfaces. 

HOW BLUETOOTH WORKS:-

The Bluetooth protocol operates at 2.4GHz in the same unlicensed ISM frequency band where RF protocols like ZigBee and WiFi also exist. 

Masters, Slaves, and Piconets

• Bluetooth networks (commonly referred to as piconets) use a master/slave model to control when and where devices can send data.

•  In this model, a single master device can be connected to up to seven different slave devices. Any slave device in the piconet can only be connected to a single master.

• The master coordinates communication throughout the piconet. It can send data to any of its slaves and request data from them as well.

•  Slaves are only allowed to transmit to and receive from their master. They can’t talk to other slaves in the piconet.

• Bluetooth Addresses and Names

• Every single Bluetooth device has a unique 48-bit address, commonly abbreviated BD_ADDR. 

• This will usually be presented in the form of a 12-digit hexadecimal value. 

• The most-significant half (24 bits) of the address is an organization unique identifier (OUI), which identifies the manufacturer. The lower 24-bits are the more unique part of the address.

Pin Configuration – AT Command

HC-05 GND — Arduino GND Pin

HC-05 VCC (5V) — Arduino 5V

HC-05 TX — Arduino Pin 10 (soft RX)

HC-05 RX — Arduino Pin11 (soft TX)

HC-05 Key (PIN 34) — Arduino Pin 9

Bluetooth – AT Mode { Steps to change data mode to AT mode}

1.  Unplug power from HC-05
2.  Upload sketch
3.  Hold in HC-05 button
4. Reconnect power to HC-05 (wait until LED blinks slowly)
5. Press Arduino reset button
6. Open Serial Monitor
7.  Make sure “Both NL & CR” is selected
8. Type AT commands

AT Commands

• AT – Check the Connection
• AT+NAME – Default name
• AT+ADDR – Default Address
• AT+VERSION – Version
• AT+UART – Baudrate
• AT+ROLE – Role of the BT module (1=Master, 0=Slave)
• AT+PSWD –Default password
• AT+CMODE – Connection Mode { 0- connect to specific addr, 1- connect any addr}
• AT+ORGL – Restore factory settings
• AT+RESET - Reset and exit AT mode

Slave Configuration

Master Configuration

Program to control the LED in the Master device by client device through push button through Bluetooth communication:-

Client Code:-

#include <SoftwareSerial.h>

SoftwareSerial BT(2,3);

#define button 8

int state = 20;

int buttonState = 0;

void setup() {

  pinMode(button, INPUT);

   BT.begin(38400);

    Serial.begin(9600);

  Serial.println("Slave Bluetooth");

}

void loop() {

 

 // Reading the button

 buttonState = digitalRead(button);

 if (buttonState == HIGH) {

  Serial.println("Sending...");

   BT.write('1');// Sends '1' to the master to turn on LED

   delay(200);

 }

 else {

   BT.write('0');

   delay(200);

 }  

}

Server Code:-

#include<SoftwareSerial.h>

SoftwareSerial BTM(2,3);

#define ledPin 10

int state = 0;

void setup()

{

  

  pinMode(ledPin, OUTPUT);

  digitalWrite(ledPin, LOW);

  BTM.begin(38400);

  Serial.begin(9600);

  Serial.println("Receiving Master");

  // Default communication rate of the Bluetooth module

}

void loop() {

 if(BTM.available() > 0){

    state = BTM.read();

    Serial.println("State of Slave");

    Serial.println(state);

    

    // Reads the data from the serial port

 }

 // Controlling the LED

 if (state == '1') {

  digitalWrite(ledPin, HIGH); // LED ON

  delay(500);

  

 }

 else if (state == '0') {

  digitalWrite(ledPin, LOW); // LED ON

 

 

 }

delay(10);

}