Easy Electronics Tutorials

Stepper motors are one of the most commonly used actuators in embedded systems where precise movement and position control are required. Unlike DC motors that rotate freely when powered, a stepper motor moves in fixed angular steps. Each step corresponds to a specific rotation angle, making it ideal for applications such as CNC machines, robotics, 3D printers, and camera sliders. In this post, we will understand the working principle of a stepper motor, the role of the ULN2003 driver IC, and how to interface a stepper motor with an ATmega16 microcontroller using embedded C. You will also see an animated connection diagram showing ATmega16 controlling the stepper motor via ULN2003.

Understanding Stepper Motors

A stepper motor converts digital pulses into small angular rotations. It consists of a rotor with teeth and stator coils arranged in phases. When the coils are energized in sequence, the rotor aligns with the magnetic field, producing a discrete step. The number of steps per revolution depends on the step angle, which is typically 1.8° or 7.5°. Stepper motors are available in two main types — Unipolar and Bipolar. The unipolar type (like 28BYJ-48) is very popular in educational setups and is easily driven by the ULN2003 IC.

ULN2003 Driver IC Overview

The ULN2003 is a 16-pin IC designed to drive inductive loads like stepper motors and relays. Each channel can sink up to 500 mA of current. The input pins are connected to the microcontroller outputs, and the corresponding output pins are connected to the motor coils. A separate pin (COM) is used to connect the motor’s supply voltage (usually +5V or +12V).

Connection Details

• ATmega16 PORTC → ULN2003 input pins (IN1–IN4)
• ULN2003 outputs → Stepper motor coil wires
• ULN2003 COM → +5V motor supply
• GND of microcontroller and motor supply must be common

C Program for Stepper Motor Interfacing with ATmega16

#include <avr/io.h>
#include <util/delay.h>

int main(void)
{
    DDRC = 0x0F; // Set PORTC lower nibble as output (PC0-PC3)
    while (1)
    {
        // Clockwise rotation sequence
        PORTC = 0b00000001;
        _delay_ms(100);
        PORTC = 0b00000010;
        _delay_ms(100);
        PORTC = 0b00000100;
        _delay_ms(100);
        PORTC = 0b00001000;
        _delay_ms(100);

        _delay_ms(500);

        // Anticlockwise rotation sequence
        PORTC = 0b00001000;
        _delay_ms(100);
        PORTC = 0b00000100;
        _delay_ms(100);
        PORTC = 0b00000010;
        _delay_ms(100);
        PORTC = 0b00000001;
        _delay_ms(100);

        _delay_ms(500);
    }
}
  

Animated Wiring Diagram — Stepper Motor Interfacing with ATmega16 and ULN2003

Working Principle

The four output pins of PORTC send control signals to the ULN2003, which in turn energizes the corresponding coils of the stepper motor. The sequence of energization determines the rotation direction. When coils are activated in the order 1-2-3-4, the motor rotates clockwise; reversing the order reverses the rotation. The delay between steps decides the motor’s speed — smaller delay means faster rotation.

Applications of Stepper Motors

• Robotics and automation projects
• 3D printers and CNC machines
• Camera sliders and gimbal systems
• Precision measuring and positioning devices

Conclusion

The stepper motor, when interfaced with ATmega16 using the ULN2003 driver IC, offers a reliable way to achieve accurate angular control. This setup is simple, cost-effective, and ideal for learning motion control in embedded systems. With minor modifications in delay and sequence, one can achieve smooth or faster movement as needed for practical applications.