Session 2: Sensing the World with IR Sensors

Goal: Connect an IR (Infrared) sensor to the micro:bit and learn the difference between analog and digital readings.

What is an IR Sensor?

An IR (Infrared) sensor can detect objects in front of it using infrared light. It’s like giving your micro:bit the ability to “see”! IR sensors are used in:

  • Robots to avoid obstacles
  • Automatic doors
  • Line-following robots
  • Proximity detection

Your IR sensor has 3 pins:

  • VCC - Power (connects to 3V)
  • GND - Ground (connects to GND)
  • OUT - Signal output (connects to Pin 0, 1, or 2)

Connecting the IR Sensor

Components You’ll Need:

  • micro:bit
  • IR sensor module
  • 3 alligator clips or jumper wires
  • Battery pack (optional, for portability)

Wiring Steps:

  1. Connect Power

    • Connect IR sensor VCC pin to micro:bit 3V pin (using red wire/clip)

  2. Connect Ground

    • Connect IR sensor GND pin to micro:bit GND pin (using black wire/clip)

  3. Connect Signal

    • Connect IR sensor OUT pin to micro:bit Pin 0 (using yellow/white wire/clip)

Safety Check: Before powering on, verify all connections with your teacher!

Understanding Digital vs Analog Readings

Sensors can send data in two ways:

Digital Reading:

  • Only two values: 0 (LOW/False) or 1 (HIGH/True)
  • Like an on/off switch
  • 0 = Object detected
  • 1 = No object detected

Analog Reading:

  • Range of values: 0 to 1023
  • Like a dimmer switch
  • Higher numbers = object is farther away
  • Lower numbers = object is closer
  • More precise than digital!

Programming the IR Sensor

Activity 1: Digital Reading (Simple Detection)

Setup:

  1. In MakeCode, go to Advanced → Pins
  2. In the on start block, add show number to display which pin you’re using
  3. Create a forever loop

In the forever block:

  1. Add an if...then...else statement
  2. From Pins, drag digital read pin P0 into the if condition
  3. Set the condition to: if digital read pin P0 = 0
  4. Then (object detected):
    • Show icon “X”
    • Play a sound (from Music)
  5. Else (path is clear):
    • Show icon “✓” (checkmark)

Test it: Wave your hand in front of the sensor! You should see an X and hear a sound when an object is detected, and a checkmark when the path is clear.

Activity 2: Analog Reading with Sound Alert

Setup:

  1. Create a new project or delete the previous code

In the forever block:

  1. Add an if...then...else statement
  2. Set the condition to: if analog read pin P0 < 300
  3. Then (object is close):
    • Show icon “X”
    • Play a sound (from Music)
  4. Else (object is far):
    • Show icon “✓” (checkmark)
  5. Add a pause 100 ms block at the end

Experiment:

  • What happens when you move your hand closer or farther?
  • Try adjusting the 300 value - what happens if you use 500? Or 200?
  • Can you find the best threshold value for detecting objects?

🎯 Challenge: Build an Obstacle Alert System

Your Task: Create a system that warns when an obstacle is getting too close!

Requirements:

  1. Use analog reading to measure distance
  2. When object is FAR (>700): Show a checkmark, no sound
  3. When object is MEDIUM (400-700): Show a small square, play a slow beep
  4. When object is CLOSE (<400): Show a large square, play a fast beep
  5. Add button A to display the current sensor reading as a number
  6. Add button B to pause/resume the system

Hints:

  • You’ll need multiple if...then...else if...else statements
  • Use the Music blocks for different beep speeds
  • Use Input blocks for button presses
  • Create a variable called systemActive to track if the system is on or off

Testing Ideas:

  • Test with different objects (hand, book, wall)
  • Find the maximum detection distance
  • See if different colored objects give different readings

Key Concepts You Learned

  • How to connect a 3-pin sensor to micro:bit
  • Difference between digital (0 or 1) and analog (0-1023) readings
  • Using conditional statements to create detection zones
  • Building a practical sensing system

Think About It:

  • Where could you use an obstacle detector in real life?
  • What other sensors could you add to make it better?
  • How could this help a robot navigate?
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