Environment Sensors

ESPGeiger can read temperature, humidity, and atmospheric pressure from a cheap I2C sensor on the same bus as the OLED. Detection is automatic at boot. Add a sensor and the values appear on /status and relevant outputs.

For wiring, pins, and per-output details see the Environment sensor configuration page.

Which one to buy

Module	What you get	Notes
AHT20 + BMP280 combo	T + H + P	Two chips on one board (AHT20 at 0x38, BMP280 at 0x76). The cheapest way to get all three readings. Often sold as a “BME280 replacement”.
BME280	T + H + P	Single-chip Bosch part, ±0.3 °C and ±3 % RH. Buy from a seller you trust — BMP280s (no humidity) are routinely re-labelled as BME280 because the chip packages look almost identical.

Either is fine for ESPGeiger’s purposes — the combo board is usually cheaper and ships in a day.

The BMP280-pretending-to-be-BME280 trap

If you bought a “BME280” and the humidity row is missing on /status, you almost certainly got a BMP280. Check the actual chip name in /info; the firmware reports what it found. There’s no firmware workaround — the chip physically doesn’t have a humidity sensor. Either return it or accept temperature + pressure only.

AHT-only modules

Bare AHT10/15/20/21/25/30 modules (no BMP280) work too — you get temperature and humidity but no pressure. Worth it only if you already have one in a drawer.

Connection

Four pins: VCC (3.3 V), GND, SDA, SCL. Shares the I2C bus with the OLED if one is fitted. Default pins per platform are listed on the configuration page.