8051 – DC Motor Interfacing

Hi all… In this tutorial we are going to learn DC Motor Interfacing with 8051. Let’s run….

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When we talk about controlling the robot, the first thing comes into the mind is controlling DC motors. Interfacing DC motor to the microcontroller is very important concept in Robotic applications. By interfacing DC motor to the microcontroller, we can do many things like controlling the direction of the motor, controlling the speed of the motor. This article describes you how to control the DC motor using AT89C51 controller.

A DC motor in simple words is a device that converts electrical energy (direct current system) into mechanical energy. It is of vital importance for the industry today.

The maximum output current of microcontroller pin is 15mA at 5V. But the power requirements of most of DC motors is out of reach of the microcontroller and even the back emf (electro motive force) which is produced by the motor may damage the microcontroller. Hence it is not good to interface DC motor directly to the controller. So use motor driver circuit in between of DC motor and controller.

Here, we are using L293D motor driver IC to drive DC motors. Using this IC, we can drive 2 DC motors at a time. For this IC motor supply is variable 4.5 to 36V and it provides maximum current of 600mA. Just refer Here for the L293d Driver’s operation.

DC Motor Interfacing with 8051

Circuit Diagram

  • Input 1 – Port 2.0
  • Input 2 – Port 2.1
  • Enable 1 – Port 2.2
  • Enable 2 – Port 2.3
  • Input 3 – Port 2.4
  • Input 4 – Port 2.5

Working Algorithm


  • EN Pin High  (En1 = 1 or En2 = 1)
  • Input 1 or Input 3 Pin High (In1 = 1 or In3=1)
  • Input 2 or Input 4 Pin Low (In2 = 0 or In4 = 0)


  • EN Pin High  (En1 = 1 or En2 = 1)
  • Input 1 or Input 3 Pin Low (In1 = 0 or In3=0)
  • Input 2 or Input 4 Pin Low (In2 = 1 or In4 = 1)


In this code First motor will rotate forward and second motor will rotate reverse.


sbit in1=P2^0;
sbit in2=P2^1;
sbit en1=P2^2;
sbit en2=P2^3;
sbit in3=P2^4;
sbit in4=P3^5;

void forward();
void reverse();

void main()
    while(1) {

void forward()

void reverse()


DC Motor Interfacing[ Please find the output image ]


  • The maximum current capacity of L293 is 600mA/channel. So do not use a motor that consumes more than that.
  • The supply voltage range of L293 is between 4.5 and 36V DC. So you can use a motor falling in that range.
  • Mostly in Robotic application we will use DC gear Motor. So same logic is used for that Gear motor also.


Just try this Tasks.

  1. Connect Switch in any port pin. Connect one DC Motor. The motor should rotate whenever i turn on the switch.
  2. If i send “F” from serial communication Motor rotate Forward direction. If i send “R”, it should rotate reverse.
  3. Program to run a motor based on the external Interrupt
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