Interfacing Bluetooth module with 8051 Microcontroller ( HC05 )

Bluetooth technology creates a big evolution in way the devices communicate with each other. So it is important to learn interfacing Bluetooth with our MCU’s to build extended system also it offers facility to wireless control. This tutorial focuses in interfacing Bluetooth module with 8051 microcontroller. We are going to use a module known as HC05 in our tutorial.

A Bluetooth module widely used with Microcontroller to enable Bluetooth communication. This module cam be interfaced using the UART in 8051 microcontroller where the data are transmitted in the form of packets. The pins TX and RX pin of the HC 05  form the path for data transmission and reception. These TX pin  of  HC05 must be connected to the RX pin of 8051 and vice versa. Whereas the key pin of the module is used to set the password for pairing the module with our devices.

Our devices such as mobile and PC’s need special applications known as “Bluetooth Terminal” to communicate with our microcontrollers via Bluetooth. Not to worry, there are plenty of apps you can find in the internet. These apps are available in plenty irrespective of the you device OS Android, Windows , Mac whatever it may be. Just run a search such as Bluetooth Terminal for “OS name” and search engines will take you to the destination.

These applications are developed in such a way to send characters through your device BT which was received by the BT module connected with our controller. Even some apps offers some interactive GUI buttons which transmits specific characters with the press of each buttons. Later the received character can be processed in our code and force the controller to perform tasks based on the received character. We can use the Bluetooth communication in two ways, either we can use it to receive data from the Controller or control the system using our device Bluetooth.

SCHEMATIC DESIGN:

STEPS TO PROGRAM:

SAMPLE CODE:

The below code was built using Keil uVision 4.

FOR RECEIVING DATA FROM CONTROLLER VIA BT:

#include<regx51.h>
#include<stdio.h>
#include<string.h> 
int a,b,ans;
char rec[4];
void main()   
{    
a=80;
b=40;
ans=a+b;
sprintf(rec, "%d", ans);
TMOD=0x20;                                //Choosing Timer mode    
TH1=0xFD;                                   //Selecting Baud Rate    
SCON=0x50;                               //Serial mode selection    
TR1=1;    
IE=0x90;                                      //Enabling Serial Interrupt    
while(1);    
}
void ser_intr(void)interrupt 4        //Subroutine for Interrupt  
{
IE=0x00;
short int i;
for(i=0;i<=2;i++)                      //Transmitting data
{
SBUF=rec[i];
while(TI==0);
TI=0;
}
IE=0x90;
}

Here a specific task is performed on interrupt occurence in the controller via BT. Consider a Motor was connected in P2.0 & P2.1 of the controller and we are about to control its direction of rotation via BT from our device. Sending character “F” will make the motor to rotate clockwise whereas “R” will make the motor to rotate in anti clockwise direction.

#include<regx51.h> 
sbit mot1=P2^0;
sbit mot2=P2^1;
void main()
{
//////////
Initialize serial communication and activate interrupts.
//////////
}
void ser_intr(void)interrupt 4        //Subroutine for Interrupt  
{
char c;
IE=0x00;
while(RI==0);
c=SBUF;
if(c=='F');                               //Controlling motor
{
mot1=1;
mot2=0;
}
else if(c=='R')
{
mot1=0;
mot2=1;
}
IE=0x90;
}

Hope you like this tutorial, leave your queries and feedback in the below comment box.