m5-clock

NTP-synchronized digital clock for M5Stack Core2.

Displays date, weekday, and time with seconds. Syncs via WiFi/NTP at startup and hourly, with RTC backup when WiFi is unavailable. Features auto brightness adjustment (night mode) and SD card configuration.

Hardware

• M5Stack Core2 (ESP32, LCD 320x240, RTC, PSRAM, battery)

Features

• Date (YYYY-MM-DD), weekday, and time (HH:MM:SS) display
• NTP time sync at startup + hourly intervals
• RTC backup when WiFi unavailable
• Night mode with auto brightness (configurable hours)
• Battery percentage display
• Static IP or DHCP
• SD card JSON configuration
• Button A: show config, Button C: manual NTP sync

Setup

Arduino IDE

1. Install board: M5Stack via Board Manager (v3.x)
2. Install libraries:
   • M5Unified
   • ArduinoJson
3. Open m5-clock/m5-clock.ino
4. Select board: M5Stack-Core2
5. Upload

SD Card Configuration

Copy sdcard/config.example.json to SD card as /config.json and edit:

{
  "wifi": {
    "ssid": "your_ssid",
    "password": "your_password"
  },
  "ntp": {
    "server": "pool.ntp.org",
    "timezone": 9,
    "daylight_offset_sec": 0
  },
  "static_ip": {
    "enabled": false,
    "ip": "192.168.1.123",
    "gateway": "192.168.1.1",
    "subnet": "255.255.255.0",
    "dns1": "8.8.8.8"
  },
  "night_mode": {
    "enabled": true,
    "start_hour": 22,
    "end_hour": 7,
    "brightness": 60,
    "day_brightness": 200
  }
}

Field	Default	Description
wifi.ssid	(empty)	WiFi SSID
wifi.password	(empty)	WiFi password
ntp.server	pool.ntp.org	NTP server
ntp.timezone	9	UTC offset in hours
ntp.daylight_offset_sec	0	DST offset in seconds
static_ip.enabled	false	Use static IP instead of DHCP
night_mode.enabled	true	Enable auto brightness
night_mode.start_hour	22	Night mode start (24h)
night_mode.end_hour	7	Night mode end (24h)
night_mode.brightness	60	LCD brightness at night (0-255)
night_mode.day_brightness	200	LCD brightness during day (0-255)

The clock works without an SD card using default settings (UTC+9, pool.ntp.org).

Architecture

m5-clock/
├── m5-clock/
│   ├── m5-clock.ino         ← main sketch (setup/loop)
│   ├── config.h             ← build-time constants
│   ├── config_manager.h     ← SD card JSON config reader
│   ├── ntp_sync.h           ← WiFi + NTP sync (UTC internally, TZ at display)
│   └── display_manager.h    ← clock/config display (sprite double-buffered)
└── sdcard/
    └── config.example.json  ← SD card config template

Technical Notes

• Time handling: NTP syncs in UTC. Timezone offset is applied at display time only, avoiding double-offset issues with M5Unified RTC.
• Night mode: M5Unified correctly controls Core2 backlight brightness. The legacy M5Core2.h setBrightness() did not work reliably.
• SD card: Core2 uses GPIO4 as SD card CS pin. Explicit SD.begin(4) is required.

Migration from v1.x

v2.0 migrates from the legacy M5Core2.h library to M5Unified:

• Requires ESP32 board package v3.x
• Remove legacy M5Core2 library if installed
• Install M5Unified via Library Manager

License

See LICENSE.