Line Following with IR Sensors

Learn how to detect and follow a line using an IR sensor and MicroPython.

Line-following robots are one of the most classic and satisfying robotics projects. In this lesson, you’ll learn how to use an IR sensor to detect a black line on a white surface and steer your robot to follow it.

🕵️ How IR Line Sensors Work

IR (infrared) sensors detect reflected light. They shine infrared light onto the surface and measure how much bounces back:

• White/light surface → reflects more → HIGH signal
• Black/dark line → absorbs more → LOW signal

Most basic IR line sensors use a digital output, but some give analog readings.

We’ll use a common TCRT5000 or similar sensor with digital output for this project.

🔌 Wiring the IR Sensor

Wire the sensor to the Pico as follows:

• VCC → 3.3V
• GND → GND
• OUT → GP6 (or any free digital pin)

If you’re using two sensors (left and right), wire the second sensor’s output to GP7.

🧪 Reading the Sensor in MicroPython

from machine import Pin
from time import sleep

# Sensor input pin
sensor = Pin(6, Pin.IN)

while True:
    if sensor.value() == 0:
        print("Line detected")
    else:
        print("No line")
    sleep(0.1)

Try placing your sensor over black tape on a white surface to see the output change.

🧠 Line Following Logic

With two sensors (left and right), you can create simple decision-making logic:

• Left sensor off, right on → turn left
• Left on, right off → turn right
• Both on → move forward
• Both off → stop or reverse

🧰 Example: Two-Sensor Line Follower

from machine import Pin, PWM
from time import sleep

# Motor pins (as in previous lesson)
# ...

# IR sensors
left_sensor = Pin(6, Pin.IN)
right_sensor = Pin(7, Pin.IN)

def forward():
    # your forward motor code here
    pass

def turn_left():
    # slow or stop left motor, run right motor
    pass

def turn_right():
    # slow or stop right motor, run left motor
    pass

def stop():
    # stop both motors
    pass

while True:
    left = left_sensor.value()
    right = right_sensor.value()

    if left == 0 and right == 1:
        turn_left()
    elif left == 1 and right == 0:
        turn_right()
    elif left == 0 and right == 0:
        forward()
    else:
        stop()

    sleep(0.05)

🧩 Try It Yourself

• Tune the logic to make turns smoother or sharper.
• Try an analog sensor and adjust thresholds.
• Experiment with different surface colors and materials.

This is your robot’s first real autonomous behavior!

Next up: Obstacle Avoidance with Ultrasonic Sensors

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