Turn Your Raspberry Pi Pico into a Robot That Obeys Lines Like a Pro

Found your Raspberry PI Pico in a cupboard that you opened 2 years before… Get along with this project to make a line follower robot using Raspberry Pi Pico and a few other Stuff

What is a Line Follower Robot?

A line follower is a type of autonomous robot that can detect and follow a line drawn on the floor, typically a black line.

Components Required

Cooking the Pi🍳

The Software Part

1. Installing Thonny IDE

• Visit: thonny’s Website

• Download it for your OS (Windows/Mac/Linux).

• Navigate to the Downloads folder after the .exe file has been downloaded in File Explorer

• Then click on the .exe file (thonny-4.1.7.exe) to execute the application and click on next until you see that the thonny is being installed

Flashing the pico with Micropython Firmware

Plug in your Pico while holding the BOOTSEL button.

1. It appears as a USB drive.
2. Go to micropython.uf2 file download for Pico
3. Download .uf2 the file and copy it to the Pico USB drive.
4. Pico will reboot into MicroPython.

Set up Thonny

• Open Thonny

• Go to Run > Select Interpreter > MicroPython (Raspberry Pi Pico)

• Select the right port.

• Paste the following MicroPython code into the script area

  Get code here or paste the code below

    
  from machine import Pin, PWM
  import time
  
  # Motor Pins
  in1 = Pin(2, Pin.OUT)
  in2 = Pin(3, Pin.OUT)
  in3 = Pin(4, Pin.OUT)
  in4 = Pin(5, Pin.OUT)
  
  ena = PWM(Pin(6))
  enb = PWM(Pin(7))
  ena.freq(1000)
  enb.freq(1000)
  
  # Sensor Pins
  sensors = [Pin(i, Pin.IN) for i in range(8, 13)]
  
  # Speed Settings
  BASE_SPEED = 35000  # Slow and safe for normal movement
  MAX_SPEED = 40000   # Max PWM limit
  TURN_SPEED = 25000  # Slower speed for turning
  
  # PID Settings
  Kp = 8000  # Proportional gain, tune this as per your bot
  Ki = 0     
  Kd = 0     
  
  # PID Variables
  previous_error = 0
  integral = 0
  
  # Motor control functions
  def set_motor_speed(left_speed, right_speed):
      left_speed = max(0, min(MAX_SPEED, left_speed))
      right_speed = max(0, min(MAX_SPEED, right_speed))
  
      if left_speed == 0:
          in1.low()
          in2.low()
      else:
          in1.high()
          in2.low()
  
      if right_speed == 0:
          in3.low()
          in4.low()
      else:
          in3.high()
          in4.low()
  
      ena.duty_u16(left_speed)
      enb.duty_u16(right_speed)
  
  def stop():
      in1.low()
      in2.low()
      in3.low()
      in4.low()
      ena.duty_u16(0)
      enb.duty_u16(0)
  
  # Read sensor values
  def read_sensors():
      return [s.value() for s in sensors]
  
  # Calculate position (PID error calculation)
  def calculate_error(sensor_values):
      weights = [-2, -1, 0, 1, 2]
      total = 0
      count = 0
      for i in range(5):
          if sensor_values[i] == 0:  # Line detected (assuming black line)
              total += weights[i]
              count += 1
      if count == 0:
          return None  # Line lost
      return total / count
  
  # PID controller
  def pid_control(error):
      global previous_error, integral
  
      if error is None:
          return 0, 0  # No correction needed if line is lost
  
      integral += error
      derivative = error - previous_error
      correction = int(Kp * error + Ki * integral + Kd * derivative)
  
      previous_error = error
  
      return correction, correction
  
  # Smart Search with PID
  def smart_search():
      global previous_error, integral  # Reset PID variables for search
      previous_error = 0
      integral = 0
  
      for attempt in range(5):
          print("Search attempt", attempt+1)
  
          # Turn left (using PID control)
          in1.low()
          in2.high()
          in3.high()
          in4.low()
          ena.duty_u16(TURN_SPEED)
          enb.duty_u16(TURN_SPEED)
          time.sleep(0.5)
          stop()
          time.sleep(0.1)
          sensor_values = read_sensors()
          error = calculate_error(sensor_values)
          left_correction, right_correction = pid_control(error)
  
          if 0 in sensor_values:
              print("Found line after left turn")
              return
  
          # Turn right (using PID control)
          in1.high()
          in2.low()
          in3.low()
          in4.high()
          ena.duty_u16(TURN_SPEED)
          enb.duty_u16(TURN_SPEED)
          time.sleep(1.0)
          stop()
          time.sleep(0.1)
          sensor_values = read_sensors()
          error = calculate_error(sensor_values)
          left_correction, right_correction = pid_control(error)
  
          if 0 in sensor_values:
              print("Found line after right turn")
              return
  
      print("Failed to find line after searching.")
  
  # Main loop
  while True:
      sensor_values = read_sensors()
      print("Sensors:", sensor_values)
  
      error = calculate_error(sensor_values)
  
      if error is None:
          print("Line lost, starting search")
          stop()
          smart_search()
      else:
          correction = int(Kp * error)
  
          left_speed = BASE_SPEED - correction
          right_speed = BASE_SPEED + correction
  
          set_motor_speed(left_speed, right_speed)
     
      time.sleep(0.01)
  

Click on the save icon

• You will get a Prompt stating:-

  Where do you want to save

  1)Raspberry Pi Pico

  2)To this PC

• Choose Pico and save the file as main.py otherwise it will not auto-run on when powered on

The Hardware part

Connections

Here is a link for the line follower connections:- Click Here

Connection Table

L298N to Pico

BFD 1000 to Pico

IR Sensor Calibration

1. Run your line follower code in Thonny.

2. You should see values being printed in the following format corresponding to each sensor:-

   Sensors: [x, x, x, x, x]

3. Place the bot on a white surface. You should see: [1, 1, 1, 1, 1] (white reflects IR = HIGH).

4. Move the centre sensor over the black line. You should see: [1, 1, 0, 1, 1] (black absorbs IR = LOW).

5. Slide the bot side to side across the line. All sensors should detect black (0) when over a line.

6. Adjust potentiometers (if needed) on the IR sensor for reliable 0/1 switching.

Test Run Video

Drive Link:-https://drive.google.com/file/d/1ODuU0T4gvLMk8YIl7x5UDorZBtHX7OeK/view?usp=sharing

That’s all, folks, for this project

Meet you in another tutorial like this

Thanks,

Shivank Dan