Control Motor Direction Using H Bridge in Embedded C

To control motor direction using an H-Bridge in Embedded C, set the two control pins connected to the H-Bridge inputs to HIGH or LOW in opposite combinations. For example, setting IN1 = HIGH and IN2 = LOW makes the motor rotate forward, while reversing these signals makes it rotate backward.

Syntax

Use two digital output pins connected to the H-Bridge inputs to control motor direction. Set pins HIGH or LOW to change rotation.

• IN1: Controls one side of the motor
• IN2: Controls the other side
• Setting IN1 = HIGH and IN2 = LOW rotates motor forward
• Setting IN1 = LOW and IN2 = HIGH rotates motor backward
• Setting both LOW or HIGH stops the motor

embedded_c

void setMotorDirection(int IN1, int IN2, int direction) {
    if(direction == 1) { // Forward
        digitalWrite(IN1, HIGH);
        digitalWrite(IN2, LOW);
    } else if(direction == 0) { // Stop
        digitalWrite(IN1, LOW);
        digitalWrite(IN2, LOW);
    } else if(direction == -1) { // Backward
        digitalWrite(IN1, LOW);
        digitalWrite(IN2, HIGH);
    }
}

Example

This example shows how to control a motor connected to pins 2 and 3 of a microcontroller using an H-Bridge. It rotates the motor forward for 3 seconds, stops for 2 seconds, then rotates backward for 3 seconds.

embedded_c

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

#define IN1_PIN PD2
#define IN2_PIN PD3

void setup() {
    DDRD |= (1 << IN1_PIN) | (1 << IN2_PIN); // Set pins as output
}

void setMotorDirection(int direction) {
    if(direction == 1) { // Forward
        PORTD |= (1 << IN1_PIN);
        PORTD &= ~(1 << IN2_PIN);
    } else if(direction == 0) { // Stop
        PORTD &= ~((1 << IN1_PIN) | (1 << IN2_PIN));
    } else if(direction == -1) { // Backward
        PORTD &= ~(1 << IN1_PIN);
        PORTD |= (1 << IN2_PIN);
    }
}

int main(void) {
    setup();
    while(1) {
        setMotorDirection(1); // Forward
        _delay_ms(3000);
        setMotorDirection(0); // Stop
        _delay_ms(2000);
        setMotorDirection(-1); // Backward
        _delay_ms(3000);
        setMotorDirection(0); // Stop
        _delay_ms(2000);
    }
    return 0;
}

Output

Motor rotates forward for 3 seconds, stops for 2 seconds, rotates backward for 3 seconds, then stops for 2 seconds, repeating.

Common Pitfalls

• Setting both H-Bridge inputs HIGH can cause a short circuit (called 'shoot-through'), damaging the motor or driver.
• Not configuring microcontroller pins as outputs will prevent motor control.
• Forgetting to stop the motor before changing direction can cause mechanical stress.
• Incorrect wiring of H-Bridge inputs to microcontroller pins leads to unexpected motor behavior.

embedded_c

/* Wrong: Both pins HIGH causes short circuit */
digitalWrite(IN1, HIGH);
digitalWrite(IN2, HIGH);

/* Right: Stop motor before reversing direction */
digitalWrite(IN1, LOW);
digitalWrite(IN2, LOW);
delay(100);
digitalWrite(IN1, LOW);
digitalWrite(IN2, HIGH); // Reverse direction

Quick Reference

IN1	IN2	Motor State
LOW	LOW	Motor stopped
HIGH	LOW	Motor rotates forward
LOW	HIGH	Motor rotates backward
HIGH	HIGH	Invalid - risk of short circuit

Key Takeaways

Use two digital pins to control motor direction via H-Bridge by setting them HIGH or LOW in opposite states.

Always stop the motor (both pins LOW) before changing direction to avoid damage.

Never set both H-Bridge inputs HIGH simultaneously to prevent short circuits.

Configure microcontroller pins as outputs before controlling the motor.

Test motor control with delays to observe direction changes safely.