DC Motor Interfacing with 8051 Microcontroller (AT89C51) – Circuit Diagram & Source Code

Introduction

DC motor interfacing with 8051 microcontroller (AT89C51) is a fundamental embedded systems project used to understand motor control, direction control, and speed variation. DC motors are widely used in robots, conveyor belts, fans, pumps, and automation systems.

In this tutorial, you will learn how to interface a DC motor with 8051, understand the working principle, motor driver IC, and control logic. This project is ideal for diploma, B.Tech, and embedded systems training students.

What is a DC Motor?

A DC motor is an electromechanical device that converts direct current electrical energy into mechanical rotation. Unlike stepper motors, DC motors rotate continuously as long as power is applied.

Key Features of DC Motor

• Simple construction

• High starting torque

• Easy speed control

• Continuous rotation

Why Use 8051 Microcontroller (AT89C51)?

The AT89C51 microcontroller is widely used for educational and industrial training projects due to its simplicity and reliability.

Features of AT89C51

• 8-bit microcontroller

• 4 KB Flash memory

• 32 I/O pins

• Timer and interrupt support

• Easy programming

Components Required

• AT89C51 Microcontroller

• DC Motor

• L293D Motor Driver IC

• Crystal Oscillator (11.0592 MHz)

• Capacitors (33pF)

• Power Supply (5V / 12V)

• Connecting Wires

• Breadboard / PCB

Why L293D Motor Driver IC is Used?

The 8051 microcontroller cannot drive a DC motor directly because DC motors require high current and voltage. The L293D is a dual H-bridge motor driver IC used to control motor direction and speed.

Advantages of L293D

• Controls motor direction (clockwise / anticlockwise)

• Built-in protection diodes

• Can drive two DC motors

• Compatible with 8051 microcontroller

Working Principle of DC Motor with 8051

The DC motor rotates when voltage is applied through the L293D motor driver. The 8051 microcontroller sends control signals to the L293D input pins.

• Logic 10 → Clockwise rotation

• Logic 01 → Anticlockwise rotation

• PWM signal → Speed control

Pin Configuration

• Port P2.0, P2.1 → L293D input pins

• L293D output pins → DC motor terminals

• Enable pin → Logic HIGH