Interfacing DC Motor with 8051 using L293D – AT89C51

In some of the electronics projects you may want to control a DC Motor with 8051 microcontroller. The maximum current that can be sourced or sunk from a 8051 microcontroller is 15 mA at 5v. But a DC Motor need currents very much more than that and it need voltages 6v, 12v, 24v etc, depending upon the type of motor used. Another problem is that the back emf produced by the motor may affect the proper functioning of the microcontroller. Due to these reasons we can’t connect a DC Motor directly to a microcontroller.

dc motor

DC Motor

To overcome these problems you may use a H-Bridge using transistors. Freewheeling diodes or Clamp diodes should be used  to avoid problems due to back emf. Thus it requires transistors, diodes and resistors, which may make our circuit bulky and difficult to assembly.

To overcome this problem the L293D driver IC is used. It is a Quadruple Half H-Bridge driver and it solves the problem completely. You needn’t connect any transistors, resistors or diodes. We can easily control the switching of L293D using a microcontroller. There are two IC’s in this category L293D and L293. L239D can provide a maximum current of 600mA from 4.5V to 36V while L293 can provide up to 1A under the same input conditions. All inputs of these ICs are TTL compatible and clamp diodes is provided with all outputs. They are used with inductive loads such as relays solenoids, motors etc.

L293D contains four Half H Bridge drivers and are enabled in pairs. EN1 is used to enable pair 1 (IN1-OUT1, IN2-OUT2) and EN2 is used to enable pair 2 (IN3-OUT3, IN4-OUT4). We can drive two DC Motors using one L293D, but here we are using only one. You can connect second DC Motor to driver pair 2 according to your needs.

Circuit Diagram

Interfacing DC Motor with 8051 using L293D

Interfacing DC Motor with 8051 using L293D

The DC Motor is connected to the first pair of drivers and it is enabled by connecting EN1 to logic HIGH (5V).  VSS pin is used to provide logic voltage to L293D. Here 8051 microcontroller, which works at 5v is used to control L293D, hence the logic voltage is 5. The motor supply is given to Vs pin of the L293D.

Keil C Program

#include<reg52.h>
#include<stdio.h>

void delay(void);

sbit motor_pin_1 = P2^0;
sbit motor_pin_2 = P2^1;

void main()
{
  do
  {
    motor_pin_1 = 1;
    motor_pin_2 = 0; //Rotates Motor Anit Clockwise
    delay();
    motor_pin_1 = 1;
    motor_pin_2 = 1; //Stops Motor
    delay();
    motor_pin_1 = 0;
    motor_pin_2 = 1; //Rotates Motor Clockwise
    delay();
    motor_pin_1 = 0;
    motor_pin_2 = 0; //Stops Motor
    delay();
  }while(1);
}

void delay()
{
  int i,j;
  for(i=0;i<1000;i++)
  {
    for(j=0;j<1000;j++)
    {
    }
  }
}

Control Signals and Motor Status

P2.0/IN1 P2.1/IN2 Motor Status
LOW LOW Stops
LOW HIGH Clockwise
HIGH LOW Anti-Clockwise
HIGH HIGH Stops

You can download Keil C files and Proteus files here…

Interfacing DC Motor with 8051 using L293D and Keil C

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  • Meenakshi

    i want to operate a dc motor using 2 switches. i.e; if i press sw1 it moves in clockwise direction ,and if i press sw2 it moves in anticlockwise direction. but they are still running in both the cases :( they won’t stop at all .what to do ?

  • http://www.electrosome.com/ Ligo George

    In proteus or hardware??
    Try stopping the motor 1 or 2 seconds before rotating it in other direction as motor has inertia…

  • Nikhita Amin

    How are you supposed to load the program onto the microcontroller(as it is without any developer board)?

  • http://www.electrosome.com/ Ligo George

    You can write program to microcontroller by using a programmer…

  • Nikhita Amin

    So I can use any programmer? It is not necessary to convert the logic level to rs232?
    All the programmers use the spi pins ,so is it that the programming doesnt change in anyway?

  • http://www.electrosome.com/ Ligo George

    You can use any AT89C51 programmer..
    I think you used a serial programmer… which is connected to PC via a USB to UART Converter…

  • Milind

    Helloo..,
    I’ve the question that can I use Atmega8 processor in place of mentioned in the ckt diagram.?
    And the programm will be same for it..?

  • gdeepkeyrun

    I used at89s52 assembled the whole circuit in bread board but didn’t worked out. I double-triple checked the connection but didn’t worked out.
    FYI-Proteus file is working perfectly.

  • gdeepkeyrun

    Is it because I am just using same 5v in 8th no. pin of L293D??