# BME280

**Bosch Sensortec** · Environmental sensor · LGA-8

Measures barometric pressure, relative humidity, and temperature in one 2.5 mm LGA package, reporting all three over I2C or SPI. Pressure resolves to about 0.18 Pa, which tracks altitude to roughly a meter, humidity reads 0 to 100% with a fast response, and the on-chip temperature both reports ambient and compensates the other two. It runs from 1.71 to 3.6 V at a few microamps in forced mode, so it fits battery weather and altitude sensing. The three-in-one upgrade of the BMP280.

## Pinout

| Pin | Name | Type | Function |
|---|---|---|---|
| 1 | GND | power_in | Ground reference for the device. Must be tied to system ground together with pin 7. |
| 2 | CSB | input | Chip select (SPI) / interface select. Tie to VDDIO to select I2C mode; drive low to select the device during SPI transactions (4-wire or 3-wire). |
| 3 | SDI/SDA | bidirectional | Serial data input. In I2C mode this is SDA; in 4-wire SPI mode this is SDI (MOSI); in 3-wire SPI mode this is the bidirectional SDI/SDO line. |
| 4 | SCK/SCL | input | Serial clock input. Acts as SCL in I2C mode and SCK in SPI mode (3- or 4-wire). |
| 5 | SDO | bidirectional | Serial data output in 4-wire SPI mode (MISO). In I2C mode this pin sets the LSB of the 7-bit slave address (GND -> address bit 0 = 0; VDDIO -> address bit 0 = 1). Do not connect (DNC) in 3-wire SPI mode. |
| 6 | VDDIO | power_in | Digital / interface supply, 1.2 V to 3.6 V. Powers the digital I/O buffers and sets the logic levels for the I2C/SPI pins. Decouple to GND with 100 nF close to the pin. |
| 7 | GND | power_in | Ground reference for the device. Tie to system ground together with pin 1. |
| 8 | VDD | power_in | Analog / main supply for the internal sensor domains, 1.71 V to 3.6 V (typ 1.8 V). Decouple to GND with 100 nF close to the pin. |

## Key specifications

| Parameter | Value |
|---|---|
| Type | Humidity + pressure + temperature sensor |
| Interface | I2C and SPI |
| Pressure | 300-1100 hPa (+/-1 hPa abs) |
| Humidity | 0-100% RH (+/-3% RH) |
| Temperature | -40 to 85 C (+/-1 C) |
| Supply | 1.71-3.6 V |
| Package | LGA-8 (2.5x2.5 mm) |

## Ordering variants

- `BME280 (LGA-8, tape & reel)`

## CAD (KiCad official)

- Symbol: `Sensor:BME280 (KiCad official)`
- Footprint: `Package_LGA:Bosch_LGA-8_2.5x2.5mm_P0.65mm_ClockwisePinNumbering`
- 3D model: LGA-8 (KiCad packages3D, STEP)
- 3D model files: `bme280-etched.step` / `bme280-etched.glb` carry the MPN laser-etched on the die in a toggleable `Adom.LaserEtch` group (Fusion-ready); `bme280.step` / `bme280.glb` are the bare package body.

## Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

- **Datasheet:** [Bosch Sensortec datasheet](https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bme280-ds002.pdf) (60 pp, sha256 `a2ccdb449fec9438`, retrieved 2026-08-17, tier: manufacturer)
- **Extractor:** `ds2sf` (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
- **CAD:** KiCad official libraries (CC-BY-SA 4.0).

[Datasheet PDF](docs/bme280-datasheet.pdf)