🛠 Low-power : extinction, sommeil et réveil

Objectives

Power the micro:bit V2 from a battery while saving energy: understand shutdown (hold reset for 3 s, or power.off), restart, and reading the cause of the restart with power.reset_reason. The V2's onboard regulator is designed for battery-powered projects (300 mA total, of which ~190 mA for the edge connector).

Hardware

• 1 micro:bit V2 board
• 1 battery with JST-PH connector (or 3V/GND via rings, never more than 3.6 V nor reversed polarity)
• 1 micro-USB cable to flash first

Complete code

from microbit import *
import power

# Au démarrage : pourquoi la carte s'est-elle réveillée ?
reason = power.reset_reason
if reason == power.ResetReason.WAKEUP_BUTTON:
    display.show(Image.YES)      # réveillée par un bouton
elif reason == power.ResetReason.SOFT_RESET:
    display.show(Image.HAPPY)
else:
    display.show(Image.THUMBS_UP)

sommeil = 0
while True:
    display.show(Image.SLEEP)
    # Compter les appuis avant extinction
    while not button_a.is_pressed and not accelerometer.was_gesture("shake"):
        sleep(100)
        # (le comptage d'événements se fait via les flags MicroPython)
    sommeil += 1
    display.scroll("REVEIL %d" % sommeil)
    sleep(1500)
    display.clear
    power.off   # extinction complète ; réveil par bouton/reset

power.off turns off the board; a physical wake-up (button A/B or pressing reset) restarts the program, which can then distinguish the origin via reset_reason. For true deep sleep with wake-up on motion interrupt, you must use the CODAL runtime (C/C++), as MicroPython does not expose a sleep API with accelerometer source.

Expected verification

After power.off, the board is completely off (black matrix, no LEDs). Pressing A turns it back on and displays a checkmark if the cause is indeed the button. On battery, battery life in shutdown is much longer than in continuous operation.

Common errors

• Believing sleep(60000) is economical: the CPU and sensors remain active, consumption is almost identical to active mode.
• Using a USB power bank: automatic cut-off at low current, the board turns off by itself — power via JST-PH or batteries.
• Confusing software shutdown and holding reset for 3 s (physical shutdown on V2): the former goes through the firmware, the latter through the hardware.
• Reusing P3/P4/P10 as GPIO without display.disable: these pins share the LED matrix columns.