bme280 v0.1.0

BME280 temperature, pressure, and humidity sensor.

Application scenarios

• Weather stations and room climate.
• Altitude estimation from pressure.
• Compensated humidity in a greenhouse or enclosure.

Contract

uint8_t bme280_init(bme280_t *device, bme280_port_t port, uint8_t i2c_address);
uint8_t bme280_read(bme280_t *device, bme280_reading_t *reading);

• read triggers a forced measurement, waits 10 ms, and compensates all three

channels with the factory calibration.

• Temperature is millidegrees Celsius; pressure is pascals; humidity is

millipercent RH.

• Returns 1 on success, 0 on a bus error or a wrong identity.

Parameters

• I2C address 0x76 or 0x77.
• Oversampling is x1 for temperature, pressure, and humidity.
• Pressure is clamped to 30000..110000 Pa; humidity to 0..100 %RH.

Memory and timing

• About 60 bytes for calibration; one 8-byte read.
• A forced measurement takes about 10 ms.

Integration

bme280_t weather;
bme280_reading_t sample;
bme280_init(&weather, board_i2c_port(), 0x76);
bme280_read(&weather, &sample);
show(sample.temperature_milli_c / 1000, sample.pressure_pa, sample.humidity_milli_percent);

Adapters

• The adapter issues a register write followed by a repeated-start read.
• Reference: BoschSensortec/BME280_driver (BSD-3-Clause), LibDriver bme280

(MIT), and the BME280 datasheet.

• This implementation is original and uses the integer compensation formulas.

When not to use

• A part that is already calibrated in a higher-level driver.
• A condensing environment without a protective membrane.

Verification

make test covers calibration parsing, a forced read, signed temperature,

pressure, humidity, and a wrong identity.

void *context;
uint8_t (*write)(void *context, uint8_t address, uint8_t reg,
const uint8_t *data, uint16_t length);
uint8_t (*read)(void *context, uint8_t address, uint8_t reg,
uint8_t *data, uint16_t length);
void (*delay_ms)(void *context, uint16_t milliseconds);

bme280_port_t port;
uint8_t i2c_address;
uint16_t t1;
int16_t t2;
int16_t t3;
uint16_t p1;
int16_t p2;
int16_t p3;
int16_t p4;
int16_t p5;
int16_t p6;
int16_t p7;
int16_t p8;
int16_t p9;
uint8_t h1;
int16_t h2;
uint8_t h3;
int16_t h4;
int16_t h5;
int8_t h6;
int32_t t_fine;

int32_t temperature_milli_c;
uint32_t pressure_pa;
uint32_t humidity_milli_percent;