bmp280.tc¶
BMP280 Temperature & Pressure Sensor Driver
// BMP280 Temperature & Pressure Sensor Driver
// I2C addresses: 0x76 (SDO=GND) or 0x77 (SDO=VCC)
// Chip ID: 0x58 (BMP280), vs 0x60 (BME280 with humidity)
// Scans both I2C buses, claims via Tasmota I2C system
// Reads every second, displays on web UI + JSON teleperiod
// Includes 6h chart history
#define BMP_ADDR1 0x76
#define BMP_ADDR2 0x77
#define BMP_ID 0x58
// Measurement results
float bmp_temp = 0.0;
float bmp_pres = 0.0;
int bmp_ok = 0;
int bmp_addr = 0;
int bmp_bus = 0;
char bmp_lbl[32];
// I2C data buffer
char bmp_buf[26];
// Calibration data (from registers 0x88..0x9F)
// Temperature
int dig_T1;
int dig_T2;
int dig_T3;
// Pressure
int dig_P1;
int dig_P2;
int dig_P3;
int dig_P4;
int dig_P5;
int dig_P6;
int dig_P7;
int dig_P8;
int dig_P9;
// t_fine is shared between temp and pressure compensation
int t_fine;
// Chart history (6h at 1 sample/min = 360 points)
#define CHART_LEN 360
float hist_temp[CHART_LEN];
float hist_pres[CHART_LEN];
int hist_pos;
int hist_tick;
// Sign-extend a 16-bit value to signed int
int sign16(int val) {
if (val >= 32768) {
return val - 65536;
}
return val;
}
// Read calibration data from sensor
int bmp_read_calib() {
// Read 24 bytes from 0x88..0x9F (temp + pressure calibration)
if (!i2cRead(bmp_addr, 0x88, bmp_buf, 24, bmp_bus)) return 0;
dig_T1 = bmp_buf[0] | (bmp_buf[1] << 8);
dig_T2 = sign16(bmp_buf[2] | (bmp_buf[3] << 8));
dig_T3 = sign16(bmp_buf[4] | (bmp_buf[5] << 8));
dig_P1 = bmp_buf[6] | (bmp_buf[7] << 8);
dig_P2 = sign16(bmp_buf[8] | (bmp_buf[9] << 8));
dig_P3 = sign16(bmp_buf[10] | (bmp_buf[11] << 8));
dig_P4 = sign16(bmp_buf[12] | (bmp_buf[13] << 8));
dig_P5 = sign16(bmp_buf[14] | (bmp_buf[15] << 8));
dig_P6 = sign16(bmp_buf[16] | (bmp_buf[17] << 8));
dig_P7 = sign16(bmp_buf[18] | (bmp_buf[19] << 8));
dig_P8 = sign16(bmp_buf[20] | (bmp_buf[21] << 8));
dig_P9 = sign16(bmp_buf[22] | (bmp_buf[23] << 8));
return 1;
}
// Configure sensor: oversampling x1 temp+press, normal mode, 1000ms standby
int bmp_configure() {
// config (0xF5): standby 1000ms (101), filter off (000), SPI off (0) = 0xA0
if (!i2cWrite8(bmp_addr, 0xF5, 0xA0, bmp_bus)) return 0;
// ctrl_meas (0xF4): temp os x1 (001), press os x1 (001), normal mode (11) = 0x27
if (!i2cWrite8(bmp_addr, 0xF4, 0x27, bmp_bus)) return 0;
return 1;
}
// Scan both buses and addresses
int bmp_scan() {
int bus = 0;
while (bus < 2) {
int addr = BMP_ADDR1;
while (addr <= BMP_ADDR2) {
if (i2cSetDevice(addr, bus)) {
// Check chip ID register (0xD0) — BMP280 = 0x58
int id = i2cRead8(addr, 0xD0, bus);
if (id == BMP_ID) {
bmp_addr = addr;
bmp_bus = bus;
i2cSetActiveFound(bmp_addr, "BMP280", bmp_bus);
return 1;
}
}
addr++;
}
bus++;
}
return 0;
}
// Compensate temperature — returns °C * 100 as int, sets t_fine
int bmp_comp_temp(int adc_T) {
int var1 = ((((adc_T >> 3) - (dig_T1 << 1))) * dig_T2) >> 11;
int var2 = (((((adc_T >> 4) - dig_T1) * ((adc_T >> 4) - dig_T1)) >> 12) * dig_T3) >> 14;
t_fine = var1 + var2;
int T = (t_fine * 5 + 128) >> 8;
return T;
}
// Compensate pressure — returns Pa as float
// Using float arithmetic to avoid 32-bit overflow
float bmp_comp_pres(int adc_P) {
float var1 = (float)t_fine / 2.0 - 64000.0;
float var2 = var1 * var1 * (float)dig_P6 / 32768.0;
var2 = var2 + var1 * (float)dig_P5 * 2.0;
var2 = var2 / 4.0 + (float)dig_P4 * 65536.0;
var1 = ((float)dig_P3 * var1 * var1 / 524288.0 + (float)dig_P2 * var1) / 524288.0;
var1 = (1.0 + var1 / 32768.0) * (float)dig_P1;
if (var1 == 0.0) return 0.0;
float p = 1048576.0 - (float)adc_P;
p = (p - var2 / 4096.0) * 6250.0 / var1;
var1 = (float)dig_P9 * p * p / 2147483648.0;
var2 = p * (float)dig_P8 / 32768.0;
p = p + (var1 + var2 + (float)dig_P7) / 16.0;
return p;
}
void EverySecond() {
if (!bmp_addr) {
if (!bmp_scan()) {
bmp_ok = 0;
return;
}
if (!bmp_read_calib()) {
bmp_ok = 0;
bmp_addr = 0;
return;
}
if (!bmp_configure()) {
bmp_ok = 0;
bmp_addr = 0;
return;
}
}
// Read 6 bytes from 0xF7: press[3], temp[3] (no humidity on BMP280)
if (!i2cRead(bmp_addr, 0xF7, bmp_buf, 6, bmp_bus)) {
bmp_ok = 0;
bmp_addr = 0;
return;
}
int adc_P = (bmp_buf[0] << 12) | (bmp_buf[1] << 4) | (bmp_buf[2] >> 4);
int adc_T = (bmp_buf[3] << 12) | (bmp_buf[4] << 4) | (bmp_buf[5] >> 4);
// Temperature (sets t_fine used by pressure)
int T100 = bmp_comp_temp(adc_T);
bmp_temp = (float)T100 / 100.0;
// Pressure in hPa
bmp_pres = bmp_comp_pres(adc_P) / 100.0;
bmp_ok = 1;
// Update chart history every minute
hist_tick++;
if (hist_tick >= 60) {
hist_tick = 0;
hist_temp[hist_pos % CHART_LEN] = bmp_temp;
hist_pres[hist_pos % CHART_LEN] = bmp_pres;
hist_pos++;
}
}
// Tasmota main page — charts
void WebPage() {
int n = hist_pos;
if (n > CHART_LEN) n = CHART_LEN;
if (n > 0) {
WebChart('l', "Temperature", "\u00b0C", 0xe74c3c, hist_pos, CHART_LEN, hist_temp, 1, 0, 0, 0);
WebChart('l', "Pressure", "hPa", 0x27ae60, hist_pos, CHART_LEN, hist_pres, 1, 0, 0, 0);
}
}
// Tasmota web UI — sensor rows
void bmp_web_label(int idx) {
char vt[32];
LGetString(idx, bmp_lbl);
strcpy(vt, "{s}BMP280 ");
strcat(vt, bmp_lbl);
strcat(vt, "{m}");
webSend(vt);
}
void WebCall() {
char buf[32];
if (bmp_ok) {
bmp_web_label(0);
sprintf(buf, "%.1f °C{e}", bmp_temp);
webSend(buf);
bmp_web_label(2);
sprintf(buf, "%.1f hPa{e}", bmp_pres);
webSend(buf);
} else {
webSend("{s}BMP280{m}not found{e}");
}
}
// JSON teleperiod — appears in MQTT sensor payload
void JsonCall() {
if (!bmp_ok) return;
char buf[96];
sprintf(buf, ",\"BMP280\":{\"Temperature\":%.1f", bmp_temp);
responseAppend(buf);
sprintf(buf, ",\"Pressure\":%.1f}", bmp_pres);
responseAppend(buf);
}
void OnExit() {
if (bmp_addr) {
I2cResetActive(bmp_addr, bmp_bus);
bmp_addr = 0;
}
}
int main() {
char buf[64];
bmp_ok = 0;
bmp_addr = 0;
hist_pos = 0;
hist_tick = 0;
if (bmp_scan()) {
sprintf(buf, "BMP280 found at 0x%x on bus %d", bmp_addr, bmp_bus);
addLog(buf);
if (bmp_read_calib() && bmp_configure()) {
addLog("BMP280 calibration loaded, sensor active");
} else {
addLog("BMP280 calibration/config failed");
bmp_addr = 0;
}
} else {
addLog("BMP280 not found on any bus");
}
return 0;
}