Shake Detector (Accelerometer) with micro:bit & Python Lesson

🎯 Objective

Students will use the micro:bit accelerometer to detect the shake gesture and respond by showing a message, image, or animation on the 5×5 LED matrix.

from microbit import *

if accelerometer.was_gesture('shake'):
    display.show(Image.SURPRISED)

🧩 Background

The accelerometer senses movement and orientation (tilts, shakes, freefall). Phones, game controllers, and wearables use similar sensors to react to motion.

🪄 Minimal Example

# Shake Detector - Minimal
from microbit import *

while True:
    if accelerometer.was_gesture('shake'):
        display.show(Image.SURPRISED)
        sleep(1000)
        display.clear()

This loop checks for a recent 'shake' and shows a surprised face for ~1 second.

📄 Spec Sheet

Functional Requirements

1. Continuously monitor accelerometer gestures.
2. On shake, display a response (image/message/animation) for ~1 second.
3. Clear the display after responding.

Non-Functional / Constraints

• Responsive loop (sleep(20–50) ms if needed).
• Avoid repeated triggers (use a simple cooldown).
• Readable, commented code (< ~50 lines for core task).

Suggested Variables

• shakes: int — total shake count (extension)
• last_event_time: int (ms) — for cooldown/debounce
• COOLDOWN_MS: int — e.g., 400–500

Test Cases

Rubric (Quick)

🧠 Pseudocode

A) Core Shake Detector

BEGIN
  IMPORT microbit module

  LOOP forever
    IF accelerometer WAS_GESTURE 'shake' THEN
      display SURPRISED image
      wait 1000 ms
      clear display
    ENDIF
  ENDLOOP
END

B) With Cooldown

BEGIN
  IMPORT microbit
  SET COOLDOWN_MS = 400
  SET last_event_time = 0

  LOOP forever
    current_time = running_time()
    IF accelerometer WAS_GESTURE 'shake' THEN
      IF (current_time - last_event_time) >= COOLDOWN_MS THEN
        show SURPRISED image for 1000 ms
        clear display
        last_event_time = current_time
      ENDIF
    ENDIF
    sleep 30
  ENDLOOP
END

C) Shake Counter + Button A (Extension)

BEGIN
  IMPORT microbit
  SET shakes = 0
  SET COOLDOWN_MS = 400
  SET last_event_time = 0

  LOOP forever
    current_time = running_time()

    IF accelerometer WAS_GESTURE 'shake' THEN
      IF (current_time - last_event_time) >= COOLDOWN_MS THEN
        shakes = shakes + 1
        show SURPRISED image for 500 ms
        clear display
        last_event_time = current_time
      ENDIF
    ENDIF

    IF button_a IS pressed THEN
      display scroll string(shakes)
    ENDIF

    sleep 30
  ENDLOOP
END

D) Multi-Gesture Response (Required)

BEGIN
  IMPORT microbit
  LOOP forever
    IF accelerometer WAS_GESTURE 'shake' THEN
      show SURPRISED (800 ms), clear
    ELSEIF accelerometer WAS_GESTURE 'left' THEN
      show ARROW_W (400 ms), clear
    ELSEIF accelerometer WAS_GESTURE 'right' THEN
      show ARROW_E (400 ms), clear
    ELSEIF accelerometer WAS_GESTURE 'freefall' THEN
      scroll "HELP!", clear
    ENDIF
    sleep 30
  ENDLOOP
END