환경 센서 활용 — BME280 온습압·SHT3x·BMP180 비교

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Bosch BME280:
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  Temperature: -40 ~ +85°C, ±1°C
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  Humidity:    0~100%RH, ±3%
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  Pressure:    300~1100 hPa, ±1 hPa
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I2C address: 0x76 (SDO=GND) or 0x77 (SDO=VDD)
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SPI: mode 0 or mode 3, max 10 MHz

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// 단순화된 float 공식 (실제는 더 복잡)
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double t_fine;
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double compensate_temp(int32_t adc_T, const calib_t *c) {
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    double var1 = (((double)adc_T) / 16384.0 - ((double)c->T1) / 1024.0) * c->T2;
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    double var2 = ((((double)adc_T) / 131072.0 - ((double)c->T1) / 8192.0) *
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                   (((double)adc_T) / 131072.0 - ((double)c->T1) / 8192.0)) * c->T3;
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    t_fine = var1 + var2;
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    return t_fine / 5120.0;   // °C
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}

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Read response: [MSB] [LSB] [CRC]
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CRC-8 polynomial: 0x31
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init: 0xFF

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#include "bme280_defs.h"
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// CS=PA4
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#define CS_LOW()  GPIOA->BSRR = (1u << (4+16))
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#define CS_HIGH() GPIOA->BSRR = (1u << 4)
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static uint8_t bme_read(uint8_t reg) {
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    uint8_t v;
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    CS_LOW();
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    spi_xfer8(reg | 0x80);   // read = bit7 set
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    v = spi_xfer8(0xFF);
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    while (SPI1->SR & SPI_SR_BSY);
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    CS_HIGH();
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    return v;
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}
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static void bme_read_n(uint8_t reg, uint8_t *buf, uint16_t n) {
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    CS_LOW();
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    spi_xfer8(reg | 0x80);
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    for (uint16_t i = 0; i < n; i++) buf[i] = spi_xfer8(0xFF);
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    while (SPI1->SR & SPI_SR_BSY);
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    CS_HIGH();
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}
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static void bme_write(uint8_t reg, uint8_t val) {
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    CS_LOW();
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    spi_xfer8(reg & 0x7F);   // write = bit7 clear
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    spi_xfer8(val);
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    while (SPI1->SR & SPI_SR_BSY);
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    CS_HIGH();
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}
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// Calibration
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typedef struct {
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    uint16_t T1; int16_t T2, T3;
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    uint16_t P1; int16_t P2, P3, P4, P5, P6, P7, P8, P9;
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    uint8_t H1; int16_t H2; uint8_t H3;
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    int16_t H4, H5; int8_t H6;
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} bme_calib_t;
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static bme_calib_t cal;
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void bme_init(void) {
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    if (bme_read(0xD0) != 0x60) {
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        printf("BME280 not found!\n");
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        return;
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    }
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    // Read calibration
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    uint8_t buf[26];
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    bme_read_n(0x88, buf, 26);
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    cal.T1 = buf[0]  | (buf[1]  << 8);
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    cal.T2 = buf[2]  | (buf[3]  << 8);
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    cal.T3 = buf[4]  | (buf[5]  << 8);
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    cal.P1 = buf[6]  | (buf[7]  << 8);
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    // ... P2-P9, H1
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    cal.H1 = buf[25];
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    bme_read_n(0xE1, buf, 7);
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    cal.H2 = buf[0] | (buf[1] << 8);
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    cal.H3 = buf[2];
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    cal.H4 = (buf[3] << 4) | (buf[4] & 0xF);
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    cal.H5 = (buf[5] << 4) | (buf[4] >> 4);
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    cal.H6 = buf[6];
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    // Configuration: humidity ×1, temp ×1, pressure ×1, normal mode
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    bme_write(0xF2, 0x01);            // ctrl_hum
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    bme_write(0xF4, (1<<5)|(1<<2)|3); // ctrl_meas: T×1, P×1, normal
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    bme_write(0xF5, (4<<5)|(0<<2));   // config: 500 ms standby, no filter
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}
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void bme_read_measurements(float *temp_c, float *pres_hpa, float *rh) {
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    uint8_t buf[8];
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    bme_read_n(0xF7, buf, 8);
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    int32_t adc_P = ((int32_t)buf[0] << 12) | ((int32_t)buf[1] << 4) | (buf[2] >> 4);
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    int32_t adc_T = ((int32_t)buf[3] << 12) | ((int32_t)buf[4] << 4) | (buf[5] >> 4);
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    int32_t adc_H = ((int32_t)buf[6] << 8)  |  buf[7];
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    *temp_c   = compensate_temp(adc_T, &cal);
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    *pres_hpa = compensate_pres(adc_P, &cal) / 100.0;
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    *rh       = compensate_humid(adc_H, &cal);
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}

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#define SHT3X_ADDR 0x44   // 또는 0x45
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static uint8_t crc8(const uint8_t *data, size_t n) {
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    uint8_t crc = 0xFF;
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    for (size_t i = 0; i < n; i++) {
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        crc ^= data[i];
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        for (int j = 0; j < 8; j++) {
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            crc = (crc & 0x80) ? (crc << 1) ^ 0x31 : (crc << 1);
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        }
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    }
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    return crc;
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}
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int sht3x_read(float *temp_c, float *rh) {
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    // Trigger single shot, high repeatability
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    uint8_t cmd[] = {0x24, 0x00};
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    i2c_write(SHT3X_ADDR, cmd, 2);
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    delay_ms(20);   // high repeatability: max 15.5 ms
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    uint8_t buf[6];
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    i2c_read(SHT3X_ADDR, buf, 6);
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    // Check CRC
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    if (crc8(&buf[0], 2) != buf[2] || crc8(&buf[3], 2) != buf[5])
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        return -1;
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    uint16_t t_raw = (buf[0] << 8) | buf[1];
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    uint16_t h_raw = (buf[3] << 8) | buf[4];
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    *temp_c = -45.0f + 175.0f * t_raw / 65535.0f;
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    *rh     = 100.0f * h_raw / 65535.0f;
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    return 0;
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}

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#define BUF 16
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static float temp_buf[BUF];
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static int buf_idx;
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float temp_smooth(float new) {
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    temp_buf[buf_idx++] = new;
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    if (buf_idx >= BUF) buf_idx = 0;
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    // sort copy, take median
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    float sorted[BUF];
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    memcpy(sorted, temp_buf, sizeof(sorted));
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    for (int i = 1; i < BUF; i++) {
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        float k = sorted[i]; int j = i - 1;
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        while (j >= 0 && sorted[j] > k) { sorted[j+1] = sorted[j]; j--; }
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        sorted[j+1] = k;
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    }
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    return sorted[BUF/2];
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}