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bmp280_i2c
for Raspberry Pi Picoโ„ข W, submitted by flashmypico

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/**
* Copyright (c) 2021 Raspberry Pi (Trading) Ltd.
*
* SPDX-License-Identifier: BSD-3-Clause
**/
#include <stdio.h>
#include "hardware/i2c.h"
#include "pico/binary_info.h"
#include "pico/stdlib.h"
/* Example code to talk to a BMP280 temperature and pressure sensor
NOTE: Ensure the device is capable of being driven at 3.3v NOT 5v. The Pico
GPIO (and therefore I2C) cannot be used at 5v.
You will need to use a level shifter on the I2C lines if you want to run the
board at 5v.
Connections on Raspberry Pi Pico board, other boards may vary.
GPIO PICO_DEFAULT_I2C_SDA_PIN (on Pico this is GP4 (pin 6)) -> SDA on BMP280
board
GPIO PICO_DEFAULT_I2C_SCK_PIN (on Pico this is GP5 (pin 7)) -> SCL on
BMP280 board
3.3v (pin 36) -> VCC on BMP280 board
GND (pin 38) -> GND on BMP280 board
*/
// device has default bus address of 0x76
#define ADDR _u(0x76)
// hardware registers
#define REG_CONFIG _u(0xF5)
#define REG_CTRL_MEAS _u(0xF4)
#define REG_RESET _u(0xE0)
#define REG_TEMP_XLSB _u(0xFC)
#define REG_TEMP_LSB _u(0xFB)
#define REG_TEMP_MSB _u(0xFA)
#define REG_PRESSURE_XLSB _u(0xF9)
#define REG_PRESSURE_LSB _u(0xF8)
#define REG_PRESSURE_MSB _u(0xF7)
// calibration registers
#define REG_DIG_T1_LSB _u(0x88)
#define REG_DIG_T1_MSB _u(0x89)
#define REG_DIG_T2_LSB _u(0x8A)
#define REG_DIG_T2_MSB _u(0x8B)
#define REG_DIG_T3_LSB _u(0x8C)
#define REG_DIG_T3_MSB _u(0x8D)
#define REG_DIG_P1_LSB _u(0x8E)
#define REG_DIG_P1_MSB _u(0x8F)
#define REG_DIG_P2_LSB _u(0x90)
#define REG_DIG_P2_MSB _u(0x91)
#define REG_DIG_P3_LSB _u(0x92)
#define REG_DIG_P3_MSB _u(0x93)
#define REG_DIG_P4_LSB _u(0x94)
#define REG_DIG_P4_MSB _u(0x95)
#define REG_DIG_P5_LSB _u(0x96)
#define REG_DIG_P5_MSB _u(0x97)
#define REG_DIG_P6_LSB _u(0x98)
#define REG_DIG_P6_MSB _u(0x99)
#define REG_DIG_P7_LSB _u(0x9A)
#define REG_DIG_P7_MSB _u(0x9B)
#define REG_DIG_P8_LSB _u(0x9C)
#define REG_DIG_P8_MSB _u(0x9D)
#define REG_DIG_P9_LSB _u(0x9E)
#define REG_DIG_P9_MSB _u(0x9F)
// number of calibration registers to be read
#define NUM_CALIB_PARAMS 24
struct bmp280_calib_param {
// temperature params
uint16_t dig_t1;
int16_t dig_t2;
int16_t dig_t3;
// pressure params
uint16_t dig_p1;
int16_t dig_p2;
int16_t dig_p3;
int16_t dig_p4;
int16_t dig_p5;
int16_t dig_p6;
int16_t dig_p7;
int16_t dig_p8;
int16_t dig_p9;
};
#ifdef i2c_default
void bmp280_init() {
// use the "handheld device dynamic" optimal setting (see datasheet)
uint8_t buf[2];
// 500ms sampling time, x16 filter
const uint8_t reg_config_val = ((0x04 << 5) | (0x05 << 2)) & 0xFC;
// send register number followed by its corresponding value
buf[0] = REG_CONFIG;
buf[1] = reg_config_val;
i2c_write_blocking(i2c_default, ADDR, buf, 2, false);
// osrs_t x1, osrs_p x4, normal mode operation
const uint8_t reg_ctrl_meas_val = (0x01 << 5) | (0x03 << 2) | (0x03);
buf[0] = REG_CTRL_MEAS;
buf[1] = reg_ctrl_meas_val;
i2c_write_blocking(i2c_default, ADDR, buf, 2, false);
}
void bmp280_read_raw(int32_t* temp, int32_t* pressure) {
// BMP280 data registers are auto-incrementing and we have 3 temperature and
// pressure registers each, so we start at 0xF7 and read 6 bytes to 0xFC
// note: normal mode does not require further ctrl_meas and config register writes
uint8_t buf[6];
uint8_t reg = REG_PRESSURE_MSB;
i2c_write_blocking(i2c_default, ADDR, &reg, 1, true); // true to keep master control of bus
i2c_read_blocking(i2c_default, ADDR, buf, 6, false); // false - finished with bus
// store the 20 bit read in a 32 bit signed integer for conversion
*pressure = (buf[0] << 12) | (buf[1] << 4) | (buf[2] >> 4);
*temp = (buf[3] << 12) | (buf[4] << 4) | (buf[5] >> 4);
}
void bmp280_reset() {
// reset the device with the power-on-reset procedure
uint8_t buf[2] = { REG_RESET, 0xB6 };
i2c_write_blocking(i2c_default, ADDR, buf, 2, false);
}
// intermediate function that calculates the fine resolution temperature
// used for both pressure and temperature conversions
int32_t bmp280_convert(int32_t temp, struct bmp280_calib_param* params) {
// use the 32-bit fixed point compensation implementation given in the
// datasheet
int32_t var1, var2;
var1 = ((((temp >> 3) - ((int32_t)params->dig_t1 << 1))) * ((int32_t)params->dig_t2)) >> 11;
var2 = (((((temp >> 4) - ((int32_t)params->dig_t1)) * ((temp >> 4) - ((int32_t)params->dig_t1))) >> 12) * ((int32_t)params->dig_t3)) >> 14;
return var1 + var2;
}
int32_t bmp280_convert_temp(int32_t temp, struct bmp280_calib_param* params) {
// uses the BMP280 calibration parameters to compensate the temperature value read from its registers
int32_t t_fine = bmp280_convert(temp, params);
return (t_fine * 5 + 128) >> 8;
}
int32_t bmp280_convert_pressure(int32_t pressure, int32_t temp, struct bmp280_calib_param* params) {
// uses the BMP280 calibration parameters to compensate the pressure value read from its registers
int32_t t_fine = bmp280_convert(temp, params);
int32_t var1, var2;
uint32_t converted = 0.0;
var1 = (((int32_t)t_fine) >> 1) - (int32_t)64000;
var2 = (((var1 >> 2) * (var1 >> 2)) >> 11) * ((int32_t)params->dig_p6);
var2 += ((var1 * ((int32_t)params->dig_p5)) << 1);
var2 = (var2 >> 2) + (((int32_t)params->dig_p4) << 16);
var1 = (((params->dig_p3 * (((var1 >> 2) * (var1 >> 2)) >> 13)) >> 3) + ((((int32_t)params->dig_p2) * var1) >> 1)) >> 18;
var1 = ((((32768 + var1)) * ((int32_t)params->dig_p1)) >> 15);
if (var1 == 0) {
return 0; // avoid exception caused by division by zero
}
converted = (((uint32_t)(((int32_t)1048576) - pressure) - (var2 >> 12))) * 3125;
if (converted < 0x80000000) {
converted = (converted << 1) / ((uint32_t)var1);
} else {
converted = (converted / (uint32_t)var1) * 2;
}
var1 = (((int32_t)params->dig_p9) * ((int32_t)(((converted >> 3) * (converted >> 3)) >> 13))) >> 12;
var2 = (((int32_t)(converted >> 2)) * ((int32_t)params->dig_p8)) >> 13;
converted = (uint32_t)((int32_t)converted + ((var1 + var2 + params->dig_p7) >> 4));
return converted;
}
void bmp280_get_calib_params(struct bmp280_calib_param* params) {
// raw temp and pressure values need to be calibrated according to
// parameters generated during the manufacturing of the sensor
// there are 3 temperature params, and 9 pressure params, each with a LSB
// and MSB register, so we read from 24 registers
uint8_t buf[NUM_CALIB_PARAMS] = { 0 };
uint8_t reg = REG_DIG_T1_LSB;
i2c_write_blocking(i2c_default, ADDR, &reg, 1, true); // true to keep master control of bus
// read in one go as register addresses auto-increment
i2c_read_blocking(i2c_default, ADDR, buf, NUM_CALIB_PARAMS, false); // false, we're done reading
// store these in a struct for later use
params->dig_t1 = (uint16_t)(buf[1] << 8) | buf[0];
params->dig_t2 = (int16_t)(buf[3] << 8) | buf[2];
params->dig_t3 = (int16_t)(buf[5] << 8) | buf[4];
params->dig_p1 = (uint16_t)(buf[7] << 8) | buf[6];
params->dig_p2 = (int16_t)(buf[9] << 8) | buf[8];
params->dig_p3 = (int16_t)(buf[11] << 8) | buf[10];
params->dig_p4 = (int16_t)(buf[13] << 8) | buf[12];
params->dig_p5 = (int16_t)(buf[15] << 8) | buf[14];
params->dig_p6 = (int16_t)(buf[17] << 8) | buf[16];
params->dig_p7 = (int16_t)(buf[19] << 8) | buf[18];
params->dig_p8 = (int16_t)(buf[21] << 8) | buf[20];
params->dig_p9 = (int16_t)(buf[23] << 8) | buf[22];
}
#endif
int main() {
stdio_init_all();
#if !defined(i2c_default) || !defined(PICO_DEFAULT_I2C_SDA_PIN) || !defined(PICO_DEFAULT_I2C_SCL_PIN)
#warning i2c / bmp280_i2c example requires a board with I2C pins
puts("Default I2C pins were not defined");
return 0;
#else
// useful information for picotool
bi_decl(bi_2pins_with_func(PICO_DEFAULT_I2C_SDA_PIN, PICO_DEFAULT_I2C_SCL_PIN, GPIO_FUNC_I2C));
bi_decl(bi_program_description("BMP280 I2C example for the Raspberry Pi Pico"));
printf("Hello, BMP280! Reading temperaure and pressure values from sensor...\n");
// I2C is "open drain", pull ups to keep signal high when no data is being sent
i2c_init(i2c_default, 100 * 1000);
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);
// configure BMP280
bmp280_init();
// retrieve fixed compensation params
struct bmp280_calib_param params;
bmp280_get_calib_params(&params);
int32_t raw_temperature;
int32_t raw_pressure;
sleep_ms(250); // sleep so that data polling and register update don't collide
while (1) {
bmp280_read_raw(&raw_temperature, &raw_pressure);
int32_t temperature = bmp280_convert_temp(raw_temperature, &params);
int32_t pressure = bmp280_convert_pressure(raw_pressure, raw_temperature, &params);
printf("Pressure = %.3f kPa\n", pressure / 1000.f);
printf("Temp. = %.2f C\n", temperature / 100.f);
// poll every 500ms
sleep_ms(500);
}
#endif
}
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This firmware image was imported from the pico-examples repository. 


Copyright 2020 (c) 2020 Raspberry Pi (Trading) Ltd.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the
following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following
   disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following
   disclaimer in the documentation and/or other materials provided with the distribution.

3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote products
   derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Homepage: https://github.com/raspberrypi/pico-examples
Repository: https://github.com/raspberrypi/pico-examples/tree/master/i2c/bmp280_i2c

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