Hardware and pin map

The reference monitor uses an ESP32 DOIT DevKit v1, Plantower PMS5003, DHT22, 16×2 I²C LCD with a PCF8574 backpack at 0x3F, and four push buttons.

Function	GPIO	Notes
LCD SDA / SCL	21 / 22	I²C
PMS5003 RX / TX	16 / 17	Serial2, 9600 baud
DHT22 data	14	Temperature and humidity
Right button	34	Falling edge; external pull-up required
Left button	35	Falling edge; external pull-up required
Settings button	36	Disabled
Boot button	39	Disabled

GPIO 34, 35, 36, and 39 are input-only and have no internal pull-ups. GPIO 36/39 are disabled because an ESP32 RTC-domain erratum can trigger phantom interrupts during Wi-Fi modem-sleep wake. Rewire those buttons to non-RTC pins before enabling them in firmware.

BLE plus Wi-Fi and TLS exceeds the default application partition, so PlatformIO uses huge_app.csv: a 3 MB single-app layout without OTA updates.