/** * 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 }

This firmware image was imported from the pico-examples repository. 


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