Overview of Bluetooth

• HC-05 is a Bluetooth device used for wireless communication. It works on serial communication (USART).
• It is a 6-pin module.
• The device can be used in 2 modes; data mode and command mode.
• The data mode is used for data transfer between devices whereas command mode is used for changing the settings of the Bluetooth module.
• AT commands are required in command mode.
• The module works on 5V or 3.3V. It has an onboard 5V to 3.3V regulator.
• As the HC-05 Bluetooth module has a 3.3V level for RX/TX and the microcontroller can detect 3.3V level, so, no need to shift the transmit level of the HC-05 module. But we need to shift the transmit voltage level from the microcontroller to RX of the HC-05 module.

For more information about the HC-05 Bluetooth module and how to use it, refer to the topic Bluetooth module HC-05 in the sensors and modules section.

For information on USART in PIC18F4550 and how to use it, refer to the topic on USART in PIC18F4550 in the PIC inside section.

Connection Diagram of Bluetooth Module HC-05 to PIC18F4550

Control the LED using HC-05 Bluetooth Module and PIC18F4550

Here let’s develop a small application in which we can control LED ON-OFF through a smartphone.

This is done by interfacing PIC18F4550 with the HC-05 Bluetooth module. Data from HC-05 is received/ transmitted serially by PIC18F.

In this application, when 1 is sent from the smartphone, LED will turn ON and if 2 is sent LED will get Turned OFF. If received data is other than 1 or 2, it will return a message to mobile that select the proper option.

 Programming HC-05

1. Initialize PIC18F4550 USART communication.
2. Receive data from the HC-05 Bluetooth module.
3. Check whether it is ‘1’ or ‘2’ and take respective controlling action on the LED.

HC-05 Bluetooth Module Code for PIC18F4550

/* Interface HC-05 Bluetooth module with PIC18F4550
 * http://www.electronicwings.com
 */

#include <pic18f4550.h>
#include "Configuration_Header_File.h"
#include "USART_Header_File.h"

#define LED LATD0             
void main()
{
    OSCCON=0x72;  /* use internal oscillator frequency
                                 which is set to 8 MHz */
    char data_in;
    TRISD = 0;  /* set PORT as output port */
    USART_Init(9600);  /* initialize USART operation with 9600 baud rate */ 
    MSdelay(50);
    while(1)
    {
        data_in=USART_ReceiveChar();
        if(data_in=='1')
        {   
            LED = 0;  /* turn ON LED */
            USART_SendString("LED_ON");  /* send LED ON status to terminal */
        }
        else if(data_in=='2')
                
        {
            LED = 1;  /* turn OFF LED */
            USART_SendString("LED_OFF");  /* send LED OFF status to terminal */
        }
        else
        {
            USART_SendString(" select 1 or 2");  /* send msg to select proper option */
        }
        MSdelay(100);
    }
}

Video of LED ON and OFF using HC-05 Bluetooth and PIC18F4550