🧠 Concept

Read a 3-sensor IR array and steer a robot left/right to keep a line centered.

🌈 How IR sensors detect lines

Black tape absorbs IR → sensor reads LOW. White surface reflects IR → sensor reads HIGH (module dependent).

🧭 Wiring + Logic table

• IR_L → D4 (Arduino) / BCM 17 (Pi) / GPIO 27 (ESP32)
• IR_C → D5 / BCM 27 / GPIO 26
• IR_R → D6 / BCM 22 / GPIO 25
• Motor driver IN1/IN2 (Left), IN3/IN4 (Right) to PWM-capable pins

💻 Code (Arduino C/C++)

// 3-IR line follow (basic) with L298N driver
const int L = 4, C = 5, R = 6;
const int ENA = 9, IN1 = 8, IN2 = 7;
const int ENB = 3, IN3 = 2, IN4 = 10;

void motors(int l, int r){ analogWrite(ENA, abs(l)); analogWrite(ENB, abs(r));
  digitalWrite(IN1, l>=0); digitalWrite(IN2, l<0);
  digitalWrite(IN3, r>=0); digitalWrite(IN4, r<0); }

void setup(){
  pinMode(L,INPUT_PULLUP); pinMode(C,INPUT_PULLUP); pinMode(R,INPUT_PULLUP);
  pinMode(ENA,OUTPUT); pinMode(IN1,OUTPUT); pinMode(IN2,OUTPUT);
  pinMode(ENB,OUTPUT); pinMode(IN3,OUTPUT); pinMode(IN4,OUTPUT);
}

void loop(){
  int l = !digitalRead(L);  // invert if needed
  int c = !digitalRead(C);
  int r = !digitalRead(R);

  int base=120, turn=80;
  if(c && !l && !r) motors(base,base);
  else if(l && c && !r) motors(base-turn, base+turn);
  else if(!l && c && r) motors(base+turn, base-turn);
  else if(l && !c && !r) motors(0, base);         // hard right
  else if(!l && !c && r) motors(base, 0);         // hard left
  else motors(0,0);                                // lost
}

🐍 Code (Raspberry Pi – Python, gpiozero)

# Line following with gpiozero
from gpiozero import DigitalInputDevice, Motor
from time import sleep

L = DigitalInputDevice(17)   # BCM
C = DigitalInputDevice(27)
R = DigitalInputDevice(22)

left = Motor(forward=5, backward=6)   # PWM pins via motor HAT/driver mapping
right = Motor(forward=13, backward=19)

def drive(l, r):  # values -1..1
    left.forward(l) if l >=0 else left.backward(-l)
    right.forward(r) if r >=0 else right.backward(-r)

while True:
    l = not L.value; c = not C.value; r = not R.value   # invert if needed
    base, t = 0.6, 0.4
    if c and not l and not r: drive(base, base)
    elif l and c and not r:   drive(base-t, base+t)
    elif not l and c and r:   drive(base+t, base-t)
    elif l and not c and not r: drive(0, base)
    elif not l and not c and r: drive(base, 0)
    else: drive(0,0)
    sleep(0.02)

⚡ Code (ESP32 – MicroPython)

# Line following on ESP32 (MicroPython)
from machine import Pin, PWM
from time import sleep

L = Pin(27, Pin.IN, Pin.PULL_UP)
C = Pin(26, Pin.IN, Pin.PULL_UP)
R = Pin(25, Pin.IN, Pin.PULL_UP)

ENA = PWM(Pin(14), freq=1000); IN1 = Pin(12, Pin.OUT); IN2 = Pin(13, Pin.OUT)
ENB = PWM(Pin(27-13), freq=1000)  # placeholder if using another pin; adjust!
IN3 = Pin(33, Pin.OUT); IN4 = Pin(32, Pin.OUT)

def motor_left(v):  # v -1..1
    d = int(abs(v)*1023)
    ENA.duty(d); IN1.value(1 if v>=0 else 0); IN2.value(0 if v>=0 else 1)
def motor_right(v):
    d = int(abs(v)*1023)
    ENB.duty(d); IN3.value(1 if v>=0 else 0); IN4.value(0 if v>=0 else 1)

def drive(l,r): motor_left(l); motor_right(r)

while True:
    l = not L.value(); c = not C.value(); r = not R.value()
    base, t = 0.6, 0.4
    if c and not l and not r: drive(base, base)
    elif l and c and not r:   drive(base-t, base+t)
    elif not l and c and r:   drive(base+t, base-t)
    elif l and not c and not r: drive(0, base)
    elif not l and not c and r: drive(base, 0)
    else: drive(0,0)
    sleep(0.02)

🛠️ Tip: tune delay & threshold

Slow things down if it oscillates. Some arrays have analog outputs—use thresholds to smooth noise.

🖨️ Worksheet — Line Tracker Tuning Sheet

• [ ] Record base speed, turn gain
• [ ] Try three tape colours & note sensor readings
• [ ] What settings gave the smoothest lap?