Environment sensor

ESPGeiger reads temperature, humidity and pressure off an I2C sensor wired to the device. Plug a supported one in, power up, and it’s picked up automatically - nothing to flash, nothing to configure. The readings land on the /status page under the radiation numbers and go out on every channel (MQTT, Webhook, WebAPI, UDP, Serial templates, Thingspeak).

Supported sensors

Chip	I2C address	Provides	Notes
BME280	0x76 / 0x77	T + H + P	Most common, ±0.3 °C, ±3 % RH
BMP280	0x76 / 0x77	T + P	No humidity, often mis-sold as BME280
AHT10 / AHT15	0x38	T + H	Older Asair part
AHT20 / AHT21	0x38	T + H	The dominant AHT module today
AHT25	0x38	T + H	Precision-binned, ±0.2 °C
AHT30	0x38	T + H	Wider temperature range (-40 to 120 °C)
AHT20 + BMP280 (combo)	0x38 + 0x76	T + H + P	Sold as “BME280 replacement” - both chips on one board

Other Bosch parts (BMP180, BMP380, BME680) and other vendor parts (SHT4x, HTU21D, DPS310, etc.) are not currently supported.

Wiring

Connect SDA, SCL, VCC (3.3 V), GND. Default pins:

Platform	SDA	SCL
ESP8266	4	5
ESP32 (classic)	21	22
ESP32-S2 / S3	8	9
ESP32-C3 / C6	6	7

If your build also has an OLED, the sensor must share the same I2C pins as the OLED. ESPGeiger uses a single I2C bus.

If you need different pins, change them in Configuration → Environment. A reboot is required to apply pin changes.

Settings

Setting	Default	Range
`env.sda`	platform default	0 - MAX_GPIO
`env.scl`	platform default	0 - MAX_GPIO
`env.unit`	0 (°C)	0=°C, 1=°F, 2=K

env.unit only affects what is shown on the local /status page and Serial templates. All outputs (MQTT, Webhook, WebAPI, UDP, Thingspeak) always publish in canonical units (°C, %RH, hPa) so consumers can convert if they want.

Combo modules

The popular AliExpress “AHT20+BMP280” module has two chips on one board (AHT20 at 0x38, BMP280 at 0x76). ESPGeiger detects both, composes temperature and humidity from the AHT20 (higher precision), and pressure from the BMP280. The boot log reports Env: AHTxx+BMP280 detected (serial console, or the Console panel on the /status page). The BMP280’s own temperature reading is used internally for pressure compensation but not exposed.

Output channels

When a sensor is present, the firmware adds the relevant fields to each output channel. Each field is sent independently, so a BMP280 ships temp + pressure but not humidity, an AHT alone ships temp + humidity but not pressure.

/status page: a single “Env” row appears under the radiation readings, e.g. 22.4°C 45% 1013 hPa. Updates live with the rest of the status polling.
MQTT: tele/sensor JSON gains t / h / p, and the legacy topics stat/T / stat/H / stat/P. Home Assistant autodiscovery publishes one sensor entity per available field.
Webhook: JSON body gains t / h / p.
WebAPI: MsgPack payload gains t / h / p.
UDP / OSC: new /espg/<id>/env schema ,fff (temp, humidity, pressure) every 60 s.
Thingspeak: maps temp / humidity / pressure to field5 / field6 / field7. Configure those fields in your Thingspeak channel UI.
Serial template (sout.format=5): variables {t} {h} {p} available for substitution.

Historical trends are not stored on the device - if you want a 24-hour chart, point your MQTT broker at Home Assistant, Grafana, or any other dashboard tool.

Diagnostics

Visit /vars.json on the device to see the current rendered value of every variable, including environmental ones. Useful when authoring Serial templates or debugging a missing humidity reading.

Troubleshooting

Env row missing on /status. No sensor was found at boot. Check 3.3 V supply, pull-up resistors (4.7 kΩ typical), SDA/SCL wiring, and the env.sda / env.scl pref values. Enable debug logging to see the probe attempt in the console.
Humidity missing from the row. You probably have a BMP280, not a BME280. The two parts look similar on a board but only BME280 has the humidity sensor. The boot log line Env: <chip> detected tells you which one you have (serial console, or the Console panel on the /status page).
Pressure missing. You probably have an AHT-only module without the paired BMP280. Add a BMP280 on the same I2C bus, or accept that pressure is not available.
Wrong temperature just after boot. The first reading sets the baseline. Allow 30 seconds for the smoothed value to settle.