BME280 sensor API

Introduction

This package contains the Bosch Sensortec's BME280 pressure sensor driver (sensor API)

The sensor driver package includes bme280.c, bme280.h and bme280_defs.h files.

Integration details

• Integrate bme280.h, bme280_defs.h and bme280.c file in to the project.
• Include the bme280.h file in your code like below.

#include "bme280.h"

File information

• bme280_defs.h : This header file has the constants, macros and datatype declarations.
• bme280.h : This header file contains the declarations of the sensor driver APIs.
• bme280.c : This source file contains the definitions of the sensor driver APIs.

Supported sensor interfaces

• SPI 4-wire
• I2C

SPI 3-wire is currently not supported in the API.

Usage guide

Initializing the sensor

To initialize the sensor, user need to create a device structure. User can do this by creating an instance of the structure bme280_dev. After creating the device strcuture, user need to fill in the various parameters as shown below.

Example for SPI 4-Wire

struct bme280_dev dev;
int8_t rslt = BME280_OK;

/* Sensor_0 interface over SPI with native chip select line */
dev.dev_id = 0;
dev.intf = BME280_SPI_INTF;
dev.read = user_spi_read;
dev.write = user_spi_write;
dev.delay_ms = user_delay_ms;

rslt = bme280_init(&dev);

Example for I2C

struct bme280_dev dev;
int8_t rslt = BME280_OK;

dev.dev_id = BME280_I2C_ADDR_PRIM;
dev.intf = BME280_I2C_INTF;
dev.read = user_i2c_read;
dev.write = user_i2c_write;
dev.delay_ms = user_delay_ms;

rslt = bme280_init(&dev);

Regarding compensation functions for temperature,pressure and humidity we have two implementations.

1. Double precision floating point version
2. Integer version

By default, integer version is used in the API. If the user needs the floating point version, the user has to uncomment BME280_FLOAT_ENABLE macro in bme280_defs.h file or add that to the compiler flags.

In integer compensation functions, we also have below two implementations for pressure.

1. For 32 bit machine.
2. For 64 bit machine.

By default, 64 bit variant is used in the API. If the user wants 32 bit variant, the user can disable the macro BME280_64BIT_ENABLE in bme280_defs.h file.

Sensor data units

The sensor data units depends on the following macros being enabled or not, (in bme280_defs.h file or as compiler macros)

• BME280_FLOAT_ENABLE
• BME280_64BIT_ENABLE

In case of the macro "BME280_FLOAT_ENABLE" enabled, The outputs are in double and the units are

- °C for temperature
- % relative humidity
- Pascal for pressure

In case if "BME280_FLOAT_ENABLE" is not enabled, then it is

- int32_t for temperature with the units 100 * °C
- uint32_t for humidity with the units 1024 * % relative humidity
- uint32_t for pressure
     If macro "BME280_64BIT_ENABLE" is enabled, which it is by default, the unit is 100 * Pascal
     If this macro is disabled, Then the unit is in Pascal

Stream sensor data

Stream sensor data in forced mode

int8_t stream_sensor_data_forced_mode(struct bme280_dev *dev)
{
    int8_t rslt;
    uint8_t settings_sel;
	uint32_t req_delay;
    struct bme280_data comp_data;

    /* Recommended mode of operation: Indoor navigation */
    dev->settings.osr_h = BME280_OVERSAMPLING_1X;
    dev->settings.osr_p = BME280_OVERSAMPLING_16X;
    dev->settings.osr_t = BME280_OVERSAMPLING_2X;
    dev->settings.filter = BME280_FILTER_COEFF_16;

    settings_sel = BME280_OSR_PRESS_SEL | BME280_OSR_TEMP_SEL | BME280_OSR_HUM_SEL | BME280_FILTER_SEL;

    rslt = bme280_set_sensor_settings(settings_sel, dev);
	
	/*Calculate the minimum delay required between consecutive measurement based upon the sensor enabled
     *  and the oversampling configuration. */
    req_delay = bme280_cal_meas_delay(&dev->settings);

    printf("Temperature, Pressure, Humidity\r\n");
    /* Continuously stream sensor data */
    while (1) {
        rslt = bme280_set_sensor_mode(BME280_FORCED_MODE, dev);
        /* Wait for the measurement to complete and print data @25Hz */
        dev->delay_ms(req_delay);
        rslt = bme280_get_sensor_data(BME280_ALL, &comp_data, dev);
        print_sensor_data(&comp_data);
    }
    return rslt;
}

void print_sensor_data(struct bme280_data *comp_data)
{
#ifdef BME280_FLOAT_ENABLE
        printf("%0.2f, %0.2f, %0.2f\r\n",comp_data->temperature, comp_data->pressure, comp_data->humidity);
#else
        printf("%ld, %ld, %ld\r\n",comp_data->temperature, comp_data->pressure, comp_data->humidity);
#endif
}

Stream sensor data in normal mode

int8_t stream_sensor_data_normal_mode(struct bme280_dev *dev)
{
	int8_t rslt;
	uint8_t settings_sel;
	struct bme280_data comp_data;

	/* Recommended mode of operation: Indoor navigation */
	dev->settings.osr_h = BME280_OVERSAMPLING_1X;
	dev->settings.osr_p = BME280_OVERSAMPLING_16X;
	dev->settings.osr_t = BME280_OVERSAMPLING_2X;
	dev->settings.filter = BME280_FILTER_COEFF_16;
	dev->settings.standby_time = BME280_STANDBY_TIME_62_5_MS;

	settings_sel = BME280_OSR_PRESS_SEL;
	settings_sel |= BME280_OSR_TEMP_SEL;
	settings_sel |= BME280_OSR_HUM_SEL;
	settings_sel |= BME280_STANDBY_SEL;
	settings_sel |= BME280_FILTER_SEL;
	rslt = bme280_set_sensor_settings(settings_sel, dev);
	rslt = bme280_set_sensor_mode(BME280_NORMAL_MODE, dev);

	printf("Temperature, Pressure, Humidity\r\n");
	while (1) {
		/* Delay while the sensor completes a measurement */
		dev->delay_ms(70);
		rslt = bme280_get_sensor_data(BME280_ALL, &comp_data, dev);
		print_sensor_data(&comp_data);
	}

	return rslt;
}

void print_sensor_data(struct bme280_data *comp_data)
{
#ifdef BME280_FLOAT_ENABLE
        printf("%0.2f, %0.2f, %0.2f\r\n",comp_data->temperature, comp_data->pressure, comp_data->humidity);
#else
        printf("%ld, %ld, %ld\r\n",comp_data->temperature, comp_data->pressure, comp_data->humidity);
#endif
}

Templates for function pointers

void user_delay_ms(uint32_t period)
{
    /*
     * Return control or wait,
     * for a period amount of milliseconds
     */
}

int8_t user_spi_read(uint8_t dev_id, uint8_t reg_addr, uint8_t *reg_data, uint16_t len)
{
    int8_t rslt = 0; /* Return 0 for Success, non-zero for failure */

    /*
     * The parameter dev_id can be used as a variable to select which Chip Select pin has
     * to be set low to activate the relevant device on the SPI bus
     */

    /*
     * Data on the bus should be like
     * |----------------+---------------------+-------------|
     * | MOSI           | MISO                | Chip Select |
     * |----------------+---------------------|-------------|
     * | (don't care)   | (don't care)        | HIGH        |
     * | (reg_addr)     | (don't care)        | LOW         |
     * | (don't care)   | (reg_data[0])       | LOW         |
     * | (....)         | (....)              | LOW         |
     * | (don't care)   | (reg_data[len - 1]) | LOW         |
     * | (don't care)   | (don't care)        | HIGH        |
     * |----------------+---------------------|-------------|
     */

    return rslt;
}

int8_t user_spi_write(uint8_t dev_id, uint8_t reg_addr, uint8_t *reg_data, uint16_t len)
{
    int8_t rslt = 0; /* Return 0 for Success, non-zero for failure */

    /*
     * The parameter dev_id can be used as a variable to select which Chip Select pin has
     * to be set low to activate the relevant device on the SPI bus
     */

    /*
     * Data on the bus should be like
     * |---------------------+--------------+-------------|
     * | MOSI                | MISO         | Chip Select |
     * |---------------------+--------------|-------------|
     * | (don't care)        | (don't care) | HIGH        |
     * | (reg_addr)          | (don't care) | LOW         |
     * | (reg_data[0])       | (don't care) | LOW         |
     * | (....)              | (....)       | LOW         |
     * | (reg_data[len - 1]) | (don't care) | LOW         |
     * | (don't care)        | (don't care) | HIGH        |
     * |---------------------+--------------|-------------|
     */

    return rslt;
}

int8_t user_i2c_read(uint8_t dev_id, uint8_t reg_addr, uint8_t *reg_data, uint16_t len)
{
    int8_t rslt = 0; /* Return 0 for Success, non-zero for failure */

    /*
     * The parameter dev_id can be used as a variable to store the I2C address of the device
     */

    /*
     * Data on the bus should be like
     * |------------+---------------------|
     * | I2C action | Data                |
     * |------------+---------------------|
     * | Start      | -                   |
     * | Write      | (reg_addr)          |
     * | Stop       | -                   |
     * | Start      | -                   |
     * | Read       | (reg_data[0])       |
     * | Read       | (....)              |
     * | Read       | (reg_data[len - 1]) |
     * | Stop       | -                   |
     * |------------+---------------------|
     */

    return rslt;
}

int8_t user_i2c_write(uint8_t dev_id, uint8_t reg_addr, uint8_t *reg_data, uint16_t len)
{
    int8_t rslt = 0; /* Return 0 for Success, non-zero for failure */

    /*
     * The parameter dev_id can be used as a variable to store the I2C address of the device
     */

    /*
     * Data on the bus should be like
     * |------------+---------------------|
     * | I2C action | Data                |
     * |------------+---------------------|
     * | Start      | -                   |
     * | Write      | (reg_addr)          |
     * | Write      | (reg_data[0])       |
     * | Write      | (....)              |
     * | Write      | (reg_data[len - 1]) |
     * | Stop       | -                   |
     * |------------+---------------------|
     */

    return rslt;
}