Alertoid

ESP32-based alert device that monitors HTTP endpoint availability and signals the result via LEDs. Configure Wi-Fi credentials and the monitored URL wirelessly over BLE using a companion app.

GitHub: sub4ikgg/alertoid · Firmware: 1.0.0

How it works

1. On first boot, hold the BOOT button for ~2 seconds to enter BLE configuration mode.
2. Send Wi-Fi credentials and the URL to monitor via BLE.
3. The device connects to Wi-Fi and starts polling the URL at the configured interval.
4. LEDs indicate the current state at a glance.
5. On BLE disconnect, the device restarts automatically.

BLE advertising auto-stops after ~24 seconds if no client connects.

LED States

State	Yellow	Green	Red
Waiting for Wi-Fi	blinks	blinks	off
Resource OK	off	triple-blinks, stays on	off
Resource unavailable	off	off	rapid blinks, stays on
BLE advertising	blinks	off	blinks (sync)
BLE connected	alternates with red	off	alternates with yellow

If the HTTP request fails (network error), the device retries silently on the next check cycle without changing LED state.

Hardware

Component	GPIO
Yellow LED	27
Green LED	25
Red LED	32
BOOT button	0 (built-in)

BLE Configuration

Device advertises as Alertoid-<MAC>. Connect with any BLE client that supports GATT writes.

Service UUID: 6E400001-B5A3-F393-E0A9-E50E24DCCA9E

Characteristic	UUID suffix	Direction	Payload
Wi-Fi config	...03	Write	{"ssid":"...","passphrase":"..."}
URL config	...04	Write	{"url":"...","code":200,"check_interval":30}
URL config	...07	Read	{"url":"...","code":200,"check_interval":30}
Firmware info	...05	Read	{"firmware":"1.0.0","mac":"...","serial":"..."}
Reboot	...06	Write	"reboot"

check_interval is in seconds (default: 5 s). After a reboot command, the device restarts and automatically re-enters BLE advertising mode.

Build & Flash

Requires PlatformIO.

# Build
pio run

# Flash
pio run --target upload

# Monitor serial output (115200 baud)
pio device monitor

# Flash and monitor
pio run --target upload && pio device monitor

Configuration Persistence

Settings survive reboots via ESP32 NVS (Non-Volatile Storage):

Namespace	Keys	Default
wifi_prefs	wifi_ssid, wifi_passphrase	—
res_prefs	res_url, res_code, res_interval	https://httpbin.org/status/200, 200, 50 ticks
ble	reboot (bool)	false

Project Structure

src/
├── main.cpp          # Main loop and operating mode state machine
├── debug.h           # LOG() macro
├── ble/              # BLE server and characteristics
├── led/              # LED GPIO control and blink patterns
├── resource/         # HTTPS availability check
└── wifi/             # Wi-Fi connection management
docs/
└── led-blink-spec.md # Detailed LED timing specification

License

See LICENSE.