DC Motor interfacing with L293D H-Bridge

L293D is a dual H-Bridge motor driver, So with one IC we can interface two DC motors which can be controlled in both clockwise and counter clockwise direction and if you have motor with fix direction of motion the you can make use of all the four I/Os to connect up to four DC motors. L293D has output current of 600mA and peak output current of 1.2A per channel. Moreover for protection of circuit from back EMF ouput diodes are included within the IC. The output supply (VCC2) has a wide range from 4.5V to 36V, which has made L293D a best choice for DC motor driver.

A simple schematic for interfacing a DC motor using L293D is shown below:

As you can see in the circuit, three pins are needed for interfacing a DC motor (A, B, Enable). If you want the o/p to be enabled completely then you can connect Enable to VCC and only 2 pins needed from controller to make the motor work.

As per the truth mentioned in the image above its fairly simple to program the microcontroller. Its also clear from the truth table of BJT circuit and L293D the programming will be same for both of them, just keeping in mind the allowed combinations of A and B. We will discuss about programming in C as well as assembly for running motor with the help of a microcontroller.

►Assembly programming

CODE:

L293D_A   equ P2.0          ;L293D A - Positive of Motor
L293D_B   equ P2.1          ;L293D B - Negative of Motor
L293D_E   equ P2.2          ;L293D E - Enable pin of IC

         org 0H
Main:
         acall rotate_f     ;Rotate motor forward
         acall delay        ;Let the motor rotate
         acall break        ;Stop the motor
         acall delay        ;Wait for some time
         acall rotate_b     ;Rotate motor backward
         acall delay        ;Let the motor rotate
         acall break        ;Stop the motor
         acall delay        ;Wait for some time
         sjmp  Main         ;Do this in loop
               
rotate_f:
         setb  L293D_A      ;Make Positive of motor 1
         clr   L293D_B      ;Make negative of motor 0
         setb  L293D_E      ;Enable to run the motor
         ret                ;Return from routine
       
rotate_b:
         clr   L293D_A      ;Make positive of motor 0
         setb  L293D_B      ;Make negative of motor 1
         setb  L293D_E      ;Enable to run the motor
         ret                ;Return from routine
       
break:
         clr   L293D_A      ;Make Positive of motor 0
         clr   L293D_B      ;Make negative of motor 0
         clr   L293D_E      ;Disable the o/p
         ret                ;Return from routine
       
delay:                      ;Some Delay
         mov   r7,#20H
back:    mov   r6,#FFH
back1:   mov   r5,#FFH
here:    djnz  r5, here
         djnz  r6, back1
         djnz  r7, back
         ret
 

►C programming

CODE:

#include <AT89X51.H>#define L293D_A P2_0         //Positive of motor
#define L293D_B P2_1         //Negative of motor
#define L293D_E P2_2         //Enable of L293D

// Function Prototypes
void rotate_f(void);         //Forward run funtion
void rotate_b(void);         //Backward run function
void breaks(void);           //Motor stop function
void delay(void);            //Some delay

void main(){                 //Our main function
    while(1){                //Infinite loop
                rotate_f();          //Run forward
                delay();             //Some delay
                breaks();            //Stop
                delay();             //Some delay
                rotate_b();          //Run Backwards
                delay();             //Some delay
                breaks();            //Stop
                delay();             //Some delay
        }                        //Do this infinitely
}

void rotate_f(){
        L293D_A = 1;             //Make positive of motor 1
        L293D_B = 0;             //Make negative of motor 0
        L293D_E = 1;             //Enable L293D
}

void rotate_b(){
        L293D_A = 0;             //Make positive of motor 0
        L293D_B = 1;             //Make negative of motor 1
        L293D_E = 1;             //Enable L293D
}

void breaks(){
        L293D_A = 0;             //Make positive of motor 0
        L293D_B = 0;             //Make negative of motor 0
        L293D_E = 0;             //Disable L293D
}

void delay(){                //Some delay...
    unsigned char i,j,k;
    for(i=0;i<0x20;i++)
        for(j=0;j<255;j++)
                for(k=0;k<255;k++);
}