pico-devices

An I2C driver for the BME280 humidity, pressure and temperature sensor with examples for RP2040-based boards like the Raspberry Pi Pico.

Contents

• Installation
• Examples
• Usage
• API

Installation

Assuming the Raspberry Pi Pico SDK has been successfully installed and the PICO_SDK_PATH environment variable has been appropriately set, this repository can be cloned and built with the following commands:

git clone https://github.com/fivdi/pico-devices.git
cd pico-devices
mkdir build
cd build
cmake ..
make

Examples

Examples can be found in the examples directory.

After a successful build, the list of example applications that have been built and are available for loading onto a RP2040-based board can be found by running the following command from the build directory:

find examples -type f -name "*.uf2"

Usage

The steps to perform to use a BME280 sensor are:

• Create a bme280_t
• Call bme280_init_struct to initialize the bme280_t struct with default values
• Optional: If needed, modify the sampling, filtering, standby time or mode settings in the bme280_t struct
• Call bme280_init to initialize the BME280 sensor
• Create a bme280_reading_t
• Call bme280_read to copy the sensor data from the BME280 sensor to the bme280_reading_t

Here is a complete minimalistic example that reads and prints BME280 sensor data every 200 milliseconds. The BME280 sensor is assumed to be at address 0x76 on the default I2C bus.

#include <stdio.h>

#include "pico/stdlib.h"
#include "hardware/i2c.h"

#include "sensor/bme280.h"
#include "callbacks/blocking.h"

int main(void) {
    stdio_init_all();

    gpio_set_function(PICO_DEFAULT_I2C_SDA_PIN, GPIO_FUNC_I2C);
    gpio_set_function(PICO_DEFAULT_I2C_SCL_PIN, GPIO_FUNC_I2C);
    gpio_pull_up(PICO_DEFAULT_I2C_SDA_PIN);
    gpio_pull_up(PICO_DEFAULT_I2C_SCL_PIN);

    i2c_init(i2c_default, 400000);

    bme280_t bme280;

    bme280_init_struct(&bme280, i2c_default, 0x76, &pico_callbacks_blocking);
    bme280_init(&bme280);

    for (uint32_t i = 1; ; ++i) {
        bme280_reading_t r;
        bme280_read(&bme280, &r);

        printf(
            "\n%u Temperature: %.2f°C, Pressure: %.2f Pa, Humidity: %.2f%%",
            i, r.temperature, r.pressure, r.humidity
        );

        sleep_ms(200);
    }
}

API

• Typedefs
  • bme280_t
  • bme280_reading_t
• Enumerations
  • bme280_error_t
  • bme280_mode_t
  • bme280_sampling_t
  • bme280_filter_coeff_t
  • bme280_standby_time_t
• Functions
  • bme280_init_struct
  • bme280_init
  • bme280_read
  • bme280_forced_read
  • bme280_typical_measurement_time
  • bme280_maximum_measurement_time

Typedefs

Typedef bme280_t

Used to control and read data from a BME280 sensor. Contains the following fields:

• bme280_sampling_t temperature_sampling - Controls sampling of temperature data
• bme280_sampling_t pressure_sampling - Controls sampling of pressure data
• bme280_sampling_t humidity_sampling - Controls sampling of humidity data
• bme280_filter_coeff_t filter_coefficient - Controls speed of response to the sensor inputs.
• bme280_standby_time_t standby_time - Controls the inactive standby period in normal mode
• bme280_mode_t mode - Controls the operating mode of the sensor

Typedef bme280_reading_t

A BME280 sensor reading. Contains the following fields:

• float temperature - Temperature in degrees Celsius
• float pressure - Pressure in pascal
• float humidity - Relative humidity in percent

Enumerations

Enumeration bme280_error_t

Function return values.

• BME280_OK - Success
• BME280_READ_ERROR - I2C read error
• BME280_WRITE_ERROR - I2C write error
• BME280_DEVICE_NOT_FOUND - BME280 sensor not found at specified address
• BME280_CALIBRATION_DATA_NOT_FOUND - Can't read calibration data from BME280 sensor
• BME280_FORCED_READ_NOT_ALLOWED - Forced read not allowed as the BME280 sensor is configured to run in normal mode

Enumeration bme280_mode_t

Controls the operating mode of the sensor.

• BME280_MODE_SLEEP - Sleep mode
• BME280_MODE_FORCED - Forced mode
• BME280_MODE_NORMAL - Normal mode

Enumeration bme280_sampling_t

Controls the sampling of sensor data.

• BME280_SAMPLING_OFF - Sampling off
• BME280_SAMPLING_X1 - Sampling × 1
• BME280_SAMPLING_X2 - Sampling × 2
• BME280_SAMPLING_X4 - Sampling × 4
• BME280_SAMPLING_X8 - Sampling × 8
• BME280_SAMPLING_X16 - Sampling × 16

Enumeration bme280_filter_coeff_t

The filter is used to slow down the response to the sensor inputs.

• BME280_FILTER_COEFF_OFF - Filter off
• BME280_FILTER_COEFF_2 - Filter coefficient = 2
• BME280_FILTER_COEFF_4 - Filter coefficient = 4
• BME280_FILTER_COEFF_8 - Filter coefficient = 8
• BME280_FILTER_COEFF_16 - Filter coefficient = 16

Enumeration bme280_standby_time_t

Controls the inactive standby period in normal mode.

• BME280_STANDBY_TIME_0_5_MS - 0.5 milliseconds
• BME280_STANDBY_TIME_62_5_MS - 62.5 milliseconds
• BME280_STANDBY_TIME_125_MS - 125 milliseconds
• BME280_STANDBY_TIME_250_MS - 250 milliseconds
• BME280_STANDBY_TIME_500_MS - 500 milliseconds
• BME280_STANDBY_TIME_1000_MS - 1000 milliseconds
• BME280_STANDBY_TIME_10_MS - 10 milliseconds
• BME280_STANDBY_TIME_20_MS - 20 milliseconds

Functions

bme280_init_struct

void bme280_init_struct(
    bme280_t *bme280,
    void *i2c,
    uint8_t i2c_address,
    const system_callbacks_t *callbacks
);

Initializes the bme280_t struct specified by bme280.

The BME280 sensor is assumed to be on the I2C bus specified by i2c at the I2C address specified by i2c_address.

On RP2040-based boards, the value specified by callbacks should be &pico_callbacks_blocking.

The sampling defaults for humidity, pressure and temperature are BME280_SAMPLING_X1 and the default filter coefficient is BME280_FILTER_COEFF_OFF. The default operating mode is BME280_MODE_NORMAL and the default standby period is BME280_STANDBY_TIME_0_5_MS for 0.5 milliseconds. The defaults can be modified after calling bme280_init_struct and before calling bme280_init.

bme280_init

bme280_error_t bme280_init(bme280_t *bme280);

Initializes the BME280 sensor.

bme280_read

bme280_error_t bme280_read(
    bme280_t *bme280,
    bme280_reading_t *reading
);

Reads the sensor data of the last sensor measurement from the BME280 to the bme280_reading_t specified by reading.

bme280_forced_read

bme280_error_t bme280_forced_read(
    bme280_t *bme280,
    bme280_reading_t *reading
);

Triggers a forced measurement, waits for the BME280 to complete the forced measurement and reads the sensor data from the BME280 to the bme280_reading_t specified by reading.

bme280_typical_measurement_time

uint32_t bme280_typical_measurement_time(const bme280_t *bme280);

Returns the typical measurement time in milliseconds.

The typical measurement time depends on the selected values for humidity, pressure and temperature sampling.

If BME280_SAMPLING_X1 (the default) is used for humidity, pressure and temperature sampling, the typical measurement time is 8 milliseconds.

If BME280_SAMPLING_X16 is used for humidity, pressure and temperature sampling, the typical measurement time is 98 milliseconds.

bme280_maximum_measurement_time

uint32_t bme280_maximum_measurement_time(const bme280_t *bme280);

Returns the maximum measurement time in milliseconds.

The maximum measurement time depends on the selected values for humidity, pressure and temperature oversampling.

If BME280_SAMPLING_X1 (the default) is used for humidity, pressure and temperature oversampling, the maximum measurement time is 10 milliseconds.

If BME280_SAMPLING_X16 is used for humidity, pressure and temperature oversampling, the maximum measurement time is 113 milliseconds.