Embedded C Program for Line Follower Robot

An Embedded C program for a line follower robot reads sensor inputs using if conditions and controls motors by setting output pins; for example, use if(sensor_left == 1 && sensor_right == 0) { move_left(); } to turn left when the left sensor detects the line.

Examples

Inputsensor_left=1, sensor_right=0

OutputRobot turns left

Inputsensor_left=0, sensor_right=0

OutputRobot moves forward

Inputsensor_left=0, sensor_right=1

OutputRobot turns right

How to Think About It

To build a line follower robot program, first read the sensors that detect the line. Then decide the robot's movement: if both sensors detect the line, move forward; if only the left sensor detects it, turn left; if only the right sensor detects it, turn right. Use simple if statements to check sensor values and control motor pins accordingly.

Algorithm

1

Read left and right line sensors

2

If both sensors detect line, move forward

3

If only left sensor detects line, turn left

4

If only right sensor detects line, turn right

5

If no sensor detects line, stop or search

Code

embedded_c

#include <avr/io.h>
#define LEFT_SENSOR (PIND & (1 << PD0))
#define RIGHT_SENSOR (PIND & (1 << PD1))

void move_forward() {
    PORTB = 0x06; // Both motors forward
}
void turn_left() {
    PORTB = 0x04; // Left motor stop, right motor forward
}
void turn_right() {
    PORTB = 0x02; // Left motor forward, right motor stop
}
void stop() {
    PORTB = 0x00; // Stop motors
}

int main(void) {
    DDRD &= ~((1 << PD0) | (1 << PD1)); // Set PD0, PD1 as input
    DDRB = 0xFF; // Set PORTB as output for motors

    while(1) {
        if (LEFT_SENSOR && RIGHT_SENSOR) {
            move_forward();
        } else if (LEFT_SENSOR && !RIGHT_SENSOR) {
            turn_left();
        } else if (!LEFT_SENSOR && RIGHT_SENSOR) {
            turn_right();
        } else {
            stop();
        }
    }
    return 0;
}

Output

No console output; robot motors controlled by PORTB pins

Dry Run

Let's trace sensor inputs through the code to see motor control decisions.

1

Sensors read

LEFT_SENSOR=1, RIGHT_SENSOR=0

2

Condition check

LEFT_SENSOR && RIGHT_SENSOR = 0 (false) LEFT_SENSOR && !RIGHT_SENSOR = 1 (true)

3

Action taken

turn_left() called, PORTB set to 0x04

LEFT_SENSOR	RIGHT_SENSOR	Action	PORTB Value
1	0	turn_left()	0x04
1	1	move_forward()	0x06
0	1	turn_right()	0x02
0	0	stop()	0x00

Why This Works

Step 1: Reading sensors

The program reads two sensors connected to input pins PD0 and PD1 using bitwise AND to detect line presence.

Step 2: Decision making

Using if conditions, the program decides the robot's movement based on which sensors detect the line.

Step 3: Motor control

Motor pins on PORTB are set to drive motors forward, turn left, right, or stop, controlling the robot's direction.

Alternative Approaches

Using ADC sensors

embedded_c

#include <avr/io.h>

int read_adc_channel(uint8_t channel) {
    ADMUX = (ADMUX & 0xF0) | (channel & 0x0F);
    ADCSRA |= (1 << ADSC);
    while (ADCSRA & (1 << ADSC));
    return ADC;
}

int main(void) {
    // Initialize ADC and motors
    // Use ADC values to decide motor control
    return 0;
}

Uses analog sensors for better line detection but requires ADC setup and more complex code.

Using interrupts for sensor change

embedded_c

// Setup external interrupts on sensor pins to react immediately
// Interrupt service routines adjust motor control
int main(void) {
    // Setup code
    while(1) {
        // Main loop can be empty or handle other tasks
    }
    return 0;
}

More responsive but more complex to implement and debug.

Complexity: O(1) time, O(1) space

Time Complexity

The program runs in an infinite loop with simple conditional checks, so each iteration runs in constant time.

Space Complexity

Uses fixed memory for variables and no dynamic allocation, so space is constant.

Which Approach is Fastest?

Direct sensor reading with simple if-else is fastest and simplest; ADC or interrupt methods add complexity and overhead.

Approach	Time	Space	Best For
Direct sensor input with if-else	O(1)	O(1)	Simple, fast line following
ADC sensor reading	O(1)	O(1)	Analog line detection, more precise
Interrupt-driven control	O(1)	O(1)	Responsive control, complex systems