Lesson 2 - AI Exploration: Face Detection

joanne.zhao Jul 01.2026

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Lesson 2 - AI Exploration: Face Detection

Students learn how to detect human faces and program the micro:bit to show a pattern when it detects a human face.

I can explain what face detection is.

I can summarize what makes face detection easier.

I can write pseudocode to plan my program.

1. Engage: What Is a Smart Gate?

We need a smarter way to run the farm: a gate that knows when someone is coming—no button needed. The technology behind it is called face detection.

Key Question

What is face detection?

Definition: Face detection is a computer vision technique that enables a program to detect human faces and locate them within images or video streams.

Let’s make a smart gate bell with face detection!

2. Explore: How Does the Camera "See" a Person?

First, make the hardware connection:

Once the hardware is connected, press the mode button to switch the AI camera to “face detection” mode. The topright LED shows which mode the camera is currently in, while the bottomright LED lights up to indicate whether a face has been detected.

Activity 1

• Build and install the hardware following the Building Instruction.

• Test and complete the table:

Action	Does it work?
In a dark classroom. In a light classroom.
Show the side face. Show the straight face.
Stand one arm's length away from the camera. Stand 3 meters away from the camera.
Cover your eyes. Cover your mouth.
Using a photo of a face.

Key Question

What conditions make face detection easy? What makes it hard?

Lighting

Orientation of face

Scale of face

Occlusion

3. Engineer: Build the Face-Detecting Bell

Part 1: Plan the Algorithm

Key Question

What should our smart bell do?

Let's describe how this algorithm should work.

This is our program's pseudocode, which is the important part of our program.

Part 2: Rebuild the Code

Go to MakeCode and add the required Extensions.

Rebuild the code.

Download the program and check the effect.

Walk in front of the camera → The “√” should show.

Walk away → The “×” should show.

4. Experience & Challenge: Build Your Smart Gate

Experience: choose your favorite bell music

Activity 2

• Guide students to explore the Music category to make the smart gate ring when it sees a face.

• Students can choose their favorite Music block or combine them to customize their program.

Challenge: Improve your smart bell

Run your program, and what do you notice?

Key Question

What will happen if you keep standing in front of the camera?

If you keep showing your face to the camera, the music loops rapidly, which is noisy and annoying.

Activity 3

• Challenge students to add the pause (ms) block in the program to wait a moment after the bell rings.

• Change the pause time to 1 second and 5 seconds. What is the difference?

5. See also: How does AI learn to detect?

Key Question

How does AI learn to detect faces?

It wasn't born with that ability. It had to learn—just like you learn to recognize things!

How does it work?

Step 1: Look at lots of pictures.

The AI was shown millions of pictures—some with faces, some without.

Step 2: Find the patterns

Over time, it discovered that face pictures always share something in common—like two dark spots on top (eyes), a line in the middle (nose), and another line below (mouth).