Revision 0:b16a9b34fa4c, committed 2016-09-06

Comitter:

Clemo

Date:

Tue Sep 06 15:17:20 2016 +0000

Commit message:

First version, works for me

Changed in this revision

diff -r 000000000000 -r b16a9b34fa4c bme280.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/bme280.cpp	Tue Sep 06 15:17:20 2016 +0000
@@ -0,0 +1,389 @@
+/*
+  bme280.cpp - driver for Bosch Sensortec BME280 combined humidity and pressure sensor.
+
+  Copyright (c) 2015 Elektor
+
+  26/11/2015 - CPV, Initial release.
+  
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General
+  Public License along with this library; if not, write to the
+  Free Software Foundation, Inc., 59 Temple Place, Suite 330,
+  Boston, MA  02111-1307  USA
+
+*/
+
+#include "bme280.h"
+
+
+BME280::BME280(void)
+{
+  _i2c_address = 0;
+  _t_fine = 0;
+  _temperature = 0;
+  _pressure = 0;
+  _humidity = 0;
+  clearCalibrationData();
+}
+
+
+void BME280::clearCalibrationData(void)
+{
+  _dig_T1 = 0;
+  _dig_T2 = 0;
+  _dig_T3 = 0;
+  _dig_P1 = 0;
+  _dig_P2 = 0;
+  _dig_P3 = 0;
+  _dig_P4 = 0;
+  _dig_P5 = 0;
+  _dig_P6 = 0;
+  _dig_P7 = 0;
+  _dig_P8 = 0;
+  _dig_P9 = 0;
+  _dig_H1 = 0;
+  _dig_H2 = 0;
+  _dig_H3 = 0;
+  _dig_H4 = 0;
+  _dig_H5 = 0;
+  _dig_H6 = 0;
+}
+
+
+uint8_t BME280::begin(uint8_t i2cAddress)
+{
+  _i2c_address = i2cAddress;
+  if (readId()==BME280_ID)
+  {
+    clearCalibrationData();
+    readCalibrationData();
+    return 0;
+  }
+  return (uint8_t)-1;
+}
+
+
+void BME280::busWrite(uint8_t *p_data, uint8_t data_size, uint8_t repeated_start)
+{
+  if (_i2c_address==BME280_I2C_ADDRESS1 || _i2c_address==BME280_I2C_ADDRESS2)
+  {
+    // Assume I2C bus.
+    i2cWrite(_i2c_address,p_data,data_size,repeated_start);
+  }
+  else
+  {
+    // Assume SPI bus.
+    // First byte is supposed to be the address of the register to write to, set R/~W bit to 0.
+    p_data[0] &= 0x7f;
+    spiWrite(p_data,data_size);
+  }
+}
+
+
+void BME280::busRead(uint8_t *p_data, uint8_t data_size)
+{
+  if (_i2c_address==BME280_I2C_ADDRESS1 || _i2c_address==BME280_I2C_ADDRESS2)
+  {
+    // Assume I2C bus.
+    i2cRead(_i2c_address,p_data,data_size);
+  }
+  else
+  {
+    // Assume SPI bus.
+    // First byte is supposed to be the address of the register to write to, set R/~W bit to 1.
+    p_data[0] |= 0x80;
+    spiRead(p_data,data_size);
+  }
+}
+
+
+uint8_t BME280::readUint8(uint8_t reg)
+{
+  uint8_t data;
+  busWrite(&reg,1,1); // Use repeated start.
+  busRead(&data,1); // Read one byte.
+  return data;
+}
+
+
+uint16_t BME280::readUint16(uint8_t reg)
+{
+  uint8_t data[2];
+  uint16_t value;
+  busWrite(&reg,1,1); // Use repeated start.
+  busRead(data,2); // Read two bytes.
+  // Process as little endian, which is the case for calibration data.
+  value = data[1];
+  value = (value<<8) | data[0];
+  return value;
+}
+
+
+void BME280::readCalibrationData(void)
+{
+  _dig_T1 = readUint16(BME280_CAL_T1);
+  _dig_T2 = (int16_t) readUint16(BME280_CAL_T2);
+  _dig_T3 = (int16_t) readUint16(BME280_CAL_T3);
+  _dig_P1 = readUint16(BME280_CAL_P1);
+  _dig_P2 = (int16_t) readUint16(BME280_CAL_P2);
+  _dig_P3 = (int16_t) readUint16(BME280_CAL_P3);
+  _dig_P4 = (int16_t) readUint16(BME280_CAL_P4);
+  _dig_P5 = (int16_t) readUint16(BME280_CAL_P5);
+  _dig_P6 = (int16_t) readUint16(BME280_CAL_P6);
+  _dig_P7 = (int16_t) readUint16(BME280_CAL_P7);
+  _dig_P8 = (int16_t) readUint16(BME280_CAL_P8);
+  _dig_P9 = (int16_t) readUint16(BME280_CAL_P9);
+  _dig_H1 = readUint8(BME280_CAL_H1);
+  _dig_H2 = (int16_t) readUint16(BME280_CAL_H2);
+  _dig_H3 = readUint8(BME280_CAL_H3);
+  // H4 & H5 share a byte.
+  uint8_t temp1 = readUint8(BME280_CAL_H4);
+  uint8_t temp2 = readUint8(BME280_CAL_H45);
+  uint8_t temp3 = readUint8(BME280_CAL_H5);
+  _dig_H4 = (temp1<<4) | (temp2&0x0f);
+  _dig_H5 = (temp3<<4) | (temp2>>4);
+  _dig_H6 = (int8_t) readUint8(BME280_CAL_H6);
+}
+
+
+uint8_t BME280::readFrom(uint8_t reg, uint8_t data_size, uint8_t *p_data)
+{
+  // Set start address to read from.
+  busWrite(&reg,1,1); // Use repeated start.
+  // Now read the requested number of bytes.
+  busRead(p_data,data_size);
+  return data_size;
+}
+
+
+void BME280::read(void)
+{
+  // Get all the measurements in one burst (recommended).
+  uint8_t data[BME280_MEASUREMENT_SIZE];
+  readFrom(BME280_MEASUREMENT_REGISTER,BME280_MEASUREMENT_SIZE,data);
+  // We assume Normal mode, so it is not necessary to reissue a Forced mode command here.
+
+  // Process data.
+  int32_t p = assembleRawValue(&data[0],1);
+  int32_t t = assembleRawValue(&data[3],1);
+  int32_t h = assembleRawValue(&data[6],0);
+
+  _temperature = compensateTemperature(t); // First call this before calling the other compensate functions.
+  _pressure = compensatePressure(p); // Uses value calculated by compensateTemperature.
+  _humidity = compensateHumidity(h); // Uses value calculated by compensateTemperature.
+}
+
+
+int32_t BME280::assembleRawValue(uint8_t *p_data, uint8_t has_xlsb)
+{
+  // Needed to decode sensor data.
+  uint32_t value = p_data[0];
+  value <<= 8;
+  value |= p_data[1];
+  if (has_xlsb!=0)
+  {
+    value <<= 4;
+    value |= (p_data[2]>>4);
+  }
+  return (int32_t) value;
+}
+
+
+void BME280::writeControlRegisters(uint8_t osrs_t, uint8_t osrs_p, uint8_t osrs_h, uint8_t mode)
+{
+  uint8_t data[2];
+  data[0] = BME280_CTRL_HUM_REGISTER;
+  data[1] = (osrs_h&0x07);
+  busWrite(data,2,0);
+  // Writing CTRL_MEAS validates previous write to CTRL_HUM.
+  data[0] = BME280_CTRL_MEAS_REGISTER;
+  data[1] = ((osrs_t&0x07)<<5) | ((osrs_p&0x07)<<2) | (mode&0x03);
+  busWrite(data,2,0);
+}
+
+
+void BME280::writeConfigRegister(uint8_t t_sb, uint8_t filter, uint8_t spi)
+{
+  uint8_t data[2];
+  data[0] = BME280_CONFIG_REGISTER;
+  data[1] = ((t_sb&0x07)<<5) | ((filter&0x07)<<2) | (spi&0x01);
+  busWrite(data,2,0);
+}
+
+
+void BME280::reset(void)
+{
+  uint8_t data[2] = { BME280_RESET_REGISTER, BME280_RESET };
+  busWrite(data,2,0);
+}
+
+
+uint8_t BME280::readId(void)
+{
+  return readUint8(BME280_ID_REGISTER);
+}
+
+
+#if BME280_ALLOW_FLOAT!=0
+
+// From the driver by Bosch Sensortec
+
+//!
+// @brief Reads actual temperature from uncompensated temperature
+// @note returns the value in Degree centigrade
+// @note Output value of "51.23" equals 51.23 DegC.
+//
+//  @param adc_T : value of uncompensated temperature
+//
+//  @return  Return the actual temperature in floating point
+//
+temperature_t BME280::compensateTemperature(int32_t adc_T)
+{
+  double v_x1_u32;
+  double v_x2_u32;
+  double temperature;
+  
+  v_x1_u32  = (((double)adc_T) / 16384.0 - ((double)_dig_T1) / 1024.0) * ((double)_dig_T2);
+  v_x2_u32  = ((((double)adc_T) / 131072.0 - ((double)_dig_T1) / 8192.0) * (((double)adc_T) / 131072.0 - ((double)_dig_T1) / 8192.0)) * ((double)_dig_T3);
+  _t_fine = (int32_t)(v_x1_u32 + v_x2_u32);
+  temperature  = (v_x1_u32 + v_x2_u32) / 5120.0;
+  return temperature;
+}
+
+
+//!
+// @brief Reads actual pressure from uncompensated pressure
+// @note Returns pressure in Pa as double.
+// @note Output value of "96386.2"
+// equals 96386.2 Pa = 963.862 hPa.
+//
+//  @param adc_P : value of uncompensated pressure
+//
+//  @return  Return the actual pressure in floating point
+//
+pressure_t BME280::compensatePressure(int32_t adc_P)
+{
+  double v_x1_u32;
+  double v_x2_u32;
+  double pressure;
+  
+  v_x1_u32 = ((double)_t_fine / 2.0) - 64000.0;
+  v_x2_u32 = v_x1_u32 * v_x1_u32 * ((double)_dig_P6) / 32768.0;
+  v_x2_u32 = v_x2_u32 + v_x1_u32 * ((double)_dig_P5) * 2.0;
+  v_x2_u32 = (v_x2_u32 / 4.0) + (((double)_dig_P4) * 65536.0);
+  v_x1_u32 = (((double)_dig_P3) * v_x1_u32 * v_x1_u32 / 524288.0 + ((double)_dig_P2) * v_x1_u32) / 524288.0;
+  v_x1_u32 = (1.0 + v_x1_u32 / 32768.0) * ((double)_dig_P1);
+  pressure = 1048576.0 - (double)adc_P;
+  // Avoid exception caused by division by zero.
+  if (v_x1_u32 != 0) pressure = (pressure - (v_x2_u32 / 4096.0)) * 6250.0 / v_x1_u32;
+  else return 0;
+  v_x1_u32 = ((double)_dig_P9) * pressure * pressure / 2147483648.0;
+  v_x2_u32 = pressure * ((double)_dig_P8) / 32768.0;
+  pressure = pressure + (v_x1_u32 + v_x2_u32 + ((double)_dig_P7)) / 16.0;
+  
+  return pressure;
+}
+
+
+//!
+// @brief Reads actual humidity from uncompensated humidity
+// @note returns the value in relative humidity (%rH)
+// @note Output value of "42.12" equals 42.12 %rH
+//
+//  @param adc_H : value of uncompensated humidity
+//
+//  @return Return the actual humidity in floating point
+//
+humidity_t BME280::compensateHumidity(int32_t adc_H)
+{
+  double var_h;
+  
+  var_h = (((double)_t_fine) - 76800.0);
+  if (var_h != 0)
+  {
+    var_h = (adc_H - (((double)_dig_H4) * 64.0 + ((double)_dig_H5) / 16384.0 * var_h)) * 
+      (((double)_dig_H2) / 65536.0 * (1.0 + ((double) _dig_H6) / 67108864.0 * 
+      var_h * (1.0 + ((double)_dig_H3) / 67108864.0 * var_h)));
+  }
+  else return 0;
+  var_h = var_h * (1.0 - ((double)_dig_H1)*var_h / 524288.0);
+  if (var_h > 100.0) var_h = 100.0;
+  else if (var_h < 0.0) var_h = 0.0;
+  return var_h;
+}
+
+#else /* BME280_ALLOW_FLOAT */
+
+// From the datasheet.
+// Returns temperature in DegC, resolution is 0.01 DegC. Output value of 5123 equals 51.23 DegC.
+// _t_fine carries fine temperature as "global" value.
+temperature_t BME280::compensateTemperature(int32_t adc_T)
+{
+  int32_t var1, var2, T;
+  var1 = ((((adc_T>>3) - ((int32_t)_dig_T1<<1))) * ((int32_t)_dig_T2)) >> 11;
+  var2 = (((((adc_T>>4) - ((int32_t)_dig_T1)) * ((adc_T>>4) - ((int32_t)_dig_T1))) >> 12) * ((int32_t)_dig_T3)) >> 14;
+  _t_fine = var1 + var2;
+  T = (_t_fine * 5 + 128) >> 8;
+  return T;
+}
+
+
+// From the datasheet.
+// Returns pressure in Pa as unsigned 32 bit integer. Output value of 96386 equals 96386 Pa = 963.86 hPa
+pressure_t BME280::compensatePressure(int32_t adc_P)
+{
+  int32_t var1, var2;
+  uint32_t p;
+  var1 = (((int32_t)_t_fine)>>1) - (int32_t)64000;
+  var2 = (((var1>>2) * (var1>>2)) >> 11 ) * ((int32_t)_dig_P6);
+  var2 = var2 + ((var1*((int32_t)_dig_P5))<<1);
+  var2 = (var2>>2)+(((int32_t)_dig_P4)<<16);
+  var1 = (((_dig_P3 * (((var1>>2) * (var1>>2)) >> 13 )) >> 3) + ((((int32_t)_dig_P2) * var1)>>1))>>18;
+  var1 =((((32768+var1))*((int32_t)_dig_P1))>>15);
+  if (var1 == 0)
+  {
+    return 0; // avoid exception caused by division by zero
+  }
+  p = (((uint32_t)(((int32_t)1048576)-adc_P)-(var2>>12)))*3125;
+  if (p < 0x80000000)
+  {
+    p = (p << 1) / ((uint32_t)var1);
+  }
+  else
+  {
+    p = (p / (uint32_t)var1) * 2;
+  }
+  var1 = (((int32_t)_dig_P9) * ((int32_t)(((p>>3) * (p>>3))>>13)))>>12;
+  var2 = (((int32_t)(p>>2)) * ((int32_t)_dig_P8))>>13;
+  p = (uint32_t)((int32_t)p + ((var1 + var2 + _dig_P7) >> 4));
+  return p;
+}
+
+
+// From the datasheet.
+// Returns humidity in %RH as unsigned 32 bit integer in Q22.10 format (22 integer and 10 fractional bits).
+// Output value of 47445 represents 47445/1024 = 46.333 %RH
+humidity_t BME280::compensateHumidity(int32_t adc_H)
+{
+  int32_t v_x1_u32r;
+  v_x1_u32r = (_t_fine - ((int32_t)76800));
+  v_x1_u32r = (((((adc_H << 14) - (((int32_t)_dig_H4) << 20) - (((int32_t)_dig_H5) * v_x1_u32r)) +
+      ((int32_t)16384)) >> 15) * (((((((v_x1_u32r * ((int32_t)_dig_H6)) >> 10) * (((v_x1_u32r *
+      ((int32_t)_dig_H3)) >> 11) + ((int32_t)32768))) >> 10) + ((int32_t)2097152)) *
+      ((int32_t)_dig_H2) + 8192) >> 14));
+  v_x1_u32r = (v_x1_u32r - (((((v_x1_u32r >> 15) * (v_x1_u32r >> 15)) >> 7) * ((int32_t)_dig_H1)) >> 4));
+  v_x1_u32r = (v_x1_u32r < 0 ? 0 : v_x1_u32r);
+  v_x1_u32r = (v_x1_u32r > 419430400 ? 419430400 : v_x1_u32r);
+  return (uint32_t)(v_x1_u32r>>12);
+}
+
+#endif /* BME280_ALLOW_FLOAT */

diff -r 000000000000 -r b16a9b34fa4c bme280.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/bme280.h	Tue Sep 06 15:17:20 2016 +0000
@@ -0,0 +1,216 @@
+/*
+  bme280.h - driver for Bosch Sensortec BME280 combined humidity and pressure sensor.
+
+  Copyright (c) 2015 Elektor
+
+  26/11/2015 - CPV, Initial release.
+  
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General
+  Public License along with this library; if not, write to the
+  Free Software Foundation, Inc., 59 Temple Place, Suite 330,
+  Boston, MA  02111-1307  USA
+
+*/
+
+#ifndef __BME280_H__
+#define __BME280_H__
+
+#include <stdint.h>
+
+
+#define BME280_ALLOW_FLOAT  (1)
+
+#if BME280_ALLOW_FLOAT!=0
+  typedef double temperature_t;
+  typedef double pressure_t;
+  typedef double humidity_t;
+#else
+  typedef int32_t temperature_t;
+  typedef uint32_t pressure_t;
+  typedef uint32_t humidity_t;
+#endif /* BME280_ALLOW_FLOAT */
+
+
+// Two possible addresses, depending on level on SDO pin.
+#define BME280_I2C_ADDRESS1  (0x76)
+#define BME280_I2C_ADDRESS2  (0x77)
+
+// Calibration registers.
+#define BME280_CAL_T1  (0x88)
+#define BME280_CAL_T2  (0x8a)
+#define BME280_CAL_T3  (0x8c)
+#define BME280_CAL_P1  (0x8e)
+#define BME280_CAL_P2  (0x90)
+#define BME280_CAL_P3  (0x92)
+#define BME280_CAL_P4  (0x94)
+#define BME280_CAL_P5  (0x96)
+#define BME280_CAL_P6  (0x98)
+#define BME280_CAL_P7  (0x9a)
+#define BME280_CAL_P8  (0x9c)
+#define BME280_CAL_P9  (0x9e)
+#define BME280_CAL_H1  (0xa1) /* 8 bits */
+#define BME280_CAL_H2  (0xe1)
+#define BME280_CAL_H3  (0xe3) /* 8 bits */
+#define BME280_CAL_H4  (0xe4) /* 12 bits, combined with H45 */
+#define BME280_CAL_H45  (0xe5) /* 12 bits, combined with H5 */
+#define BME280_CAL_H5  (0xe6) /* 8 bits */
+#define BME280_CAL_H6  (0xe7) /* 8 bits */
+
+// Control registers.
+#define BME280_ID_REGISTER  (0xd0) /* 8 bits */
+#define BME280_RESET_REGISTER  (0xe0) /* 8 bits */
+#define BME280_CTRL_HUM_REGISTER  (0xf2) /* 8 bits */
+#define BME280_STATUS_REGISTER  (0xf3) /* 8 bits */
+#define BME280_CTRL_MEAS_REGISTER  (0xf4) /* 8 bits */
+#define BME280_CONFIG_REGISTER  (0xf5) /* 8 bits */
+
+// Measurement registers.
+#define BME280_PRESSURE  (0xf7) /* 20 bits */
+#define BME280_PRESSURE_MSB  (0xf7) /* 8 bits */
+#define BME280_PRESSURE_LSB  (0xf8) /* 8 bits */
+#define BME280_PRESSURE_XLSB  (0xf9) /* 8 bits */
+#define BME280_TEMPERATURE  (0xfa) /* 20 bits */
+#define BME280_TEMPERATURE_MSB  (0xfa) /* 8 bits */
+#define BME280_TEMPERATURE_LSB  (0xfb) /* 8 bits */
+#define BME280_TEMPERATURE_XLSB  (0xfc) /* 8 bits */
+#define BME280_HUMIDITY  (0xfd) /* 16 bits */
+#define BME280_HUMIDITY_MSB  (0xfd) /* 8 bits */
+#define BME280_HUMIDITY_LSB  (0xfe) /* 8 bits */
+
+// It is recommended to read all the measurements in one go.
+#define BME280_MEASUREMENT_REGISTER  (BME280_PRESSURE)
+#define BME280_MEASUREMENT_SIZE  (8)
+
+// Values for osrs_p & osrs_t fields of CTRL_MEAS register.
+#define BME280_SKIP  (0)
+#define BME280_OVERSAMPLING_1X  (1)
+#define BME280_OVERSAMPLING_2X  (2)
+#define BME280_OVERSAMPLING_4X  (3)
+#define BME280_OVERSAMPLING_8X  (4)
+#define BME280_OVERSAMPLING_16X  (5)
+
+// Values for mode field of CTRL_MEAS register.
+#define BME280_MODE_SLEEP  (0)
+#define BME280_MODE_FORCED  (1)
+#define BME280_MODE_NORMAL  (3)
+
+// Value for RESET register.
+#define BME280_RESET  (0xb6)
+
+// Value of ID register.
+#define BME280_ID  (0x60)
+
+// Values for t_sb field of CONFIG register
+#define BME280_STANDBY_500_US  (0)
+#define BME280_STANDBY_10_MS  (6)
+#define BME280_STANDBY_20_MS  (7)
+#define BME280_STANDBY_63_MS  (1)
+#define BME280_STANDBY_125_MS  (2)
+#define BME280_STANDBY_250_MS  (3)
+#define BME280_STANDBY_500_MS  (4)
+#define BME280_STANDBY_1000_MS  (5)
+
+// Values for filter field of CONFIG register
+#define BME280_FILTER_OFF  (0)
+#define BME280_FILTER_COEFF_2  (1)
+#define BME280_FILTER_COEFF_4  (2)
+#define BME280_FILTER_COEFF_8  (3)
+#define BME280_FILTER_COEFF_16  (4)
+
+
+// I2C write function must support repeated start to avoid interruption of transactions.
+// User-provided function to write data_size bytes from buffer p_data to I2C device at bus address i2c_address.
+// Provide empty function if not used.
+extern void i2cWrite(uint8_t i2c_address, uint8_t *p_data, uint8_t data_size, uint8_t repeated_start);
+// User-provided function to read data_size bytes from I2C device at bus address i2c_address to buffer p_data.
+// Provide empty function if not used.
+extern void i2cRead(uint8_t i2c_address, uint8_t *p_data, uint8_t data_size);
+
+// SPI functions must activate (make low) BME280 CSB pin before doing a transfer
+// and deactivate it (make high) when done.
+// User-provided function to write data_size bytes from buffer p_data to SPI device.
+// Provide empty function if not used.
+extern void spiWrite(uint8_t *p_data, uint8_t data_size);
+// User-provided function to read data_size bytes from SPI device to buffer p_data.
+// Provide empty function if not used.
+extern void spiRead(uint8_t *p_data, uint8_t data_size);
+
+
+class BME280
+{
+public:
+  BME280(void);
+  uint8_t begin(uint8_t i2cAddress=0); // I2C address not set means SPI.
+
+  void readCalibrationData(void);
+  uint8_t readId(void);
+  uint8_t readFrom(uint8_t reg, uint8_t data_size, uint8_t *p_data);
+
+  void read(void);
+
+  // If using floating points, values are scaled, if not then
+  // temperature is 100*T, pressure is Pa en humidity is 1024*%RH
+  temperature_t temperature(void) { return _temperature; } // [degrees Celsius] or 100*[degrees Celsius]
+  pressure_t pressure(void) { return _pressure; } // [Pa]
+  humidity_t humidity(void) { return _humidity; } // [%RH] or 1024*[%RH]
+
+  void writeControlRegisters(uint8_t osrs_t, uint8_t osrs_p, uint8_t osrs_h, uint8_t mode);
+  void writeConfigRegister(uint8_t t_sb, uint8_t filter, uint8_t spi);
+
+  void reset(void);
+
+private:
+  uint8_t _i2c_address;
+
+  void busWrite(uint8_t *p_data, uint8_t data_size, uint8_t repeated_start);
+  void busRead(uint8_t *p_data, uint8_t data_size);
+
+  // Calibration data.
+  uint16_t _dig_T1;
+  int16_t _dig_T2;
+  int16_t _dig_T3;
+  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;
+  uint8_t _dig_H1;
+  int16_t _dig_H2;
+  uint8_t _dig_H3;
+  int16_t _dig_H4;
+  int16_t _dig_H5;
+  int8_t _dig_H6;
+  void clearCalibrationData(void);
+
+  uint8_t readUint8(uint8_t reg);
+  uint16_t readUint16(uint8_t reg);
+
+  int32_t assembleRawValue(uint8_t *p_data, uint8_t has_xlsb);
+
+  int32_t _t_fine;
+
+  temperature_t compensateTemperature(int32_t adc_T);
+  pressure_t compensatePressure(int32_t adc_P);
+  humidity_t compensateHumidity(int32_t adc_H);
+
+  temperature_t _temperature;
+  pressure_t _pressure;
+  humidity_t _humidity;
+};
+
+
+#endif /* __BME280_H__*/
\ No newline at end of file

diff -r 000000000000 -r b16a9b34fa4c main.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Tue Sep 06 15:17:20 2016 +0000
@@ -0,0 +1,102 @@
+
+#include "mbed.h"
+
+#include <stdint.h>
+#include "bme280.h"
+
+#if defined TARGET_LPC81X
+    // SDA, SCL for Elektor CoCo-ri-Co!
+    #define PIN_SDA  (P0_10)
+    #define PIN_SCL  (P0_11)
+#elif defined TARGET_NRF51_MICROBIT
+    // SDA, SCL for BBC micro:bit
+    #define PIN_SDA  I2C_SDA0 /* (P20) */
+    #define PIN_SCL  I2C_SCL0 /* (P19) */
+#endif
+
+I2C i2c(PIN_SDA,PIN_SCL);
+BME280 bme280;
+
+DigitalOut led1(LED1); // Blue on LPC800-MAX, Pad0 on micro:bit
+DigitalOut led2(LED2); // Green on LPC800-MAX, Pad1 on micro:bit
+DigitalOut led3(LED3); // Red on LPC800-MAX, Pad2 on micro:bit
+
+#if defined TARGET_LPC81X
+    #define LED_ON  (0)
+    #define LED_OFF  (1)
+#elif defined TARGET_NRF51_MICROBIT
+    #define LED_ON  (1)
+    #define LED_OFF  (0)
+#endif
+
+// Note for LPC800-MAX users: check SJ1 and SJ4. 
+// For the USB serial port to work pins 1&2 must be shorted, not pins 2&3.
+
+
+void i2cWrite(uint8_t i2c_address, uint8_t *p_data, uint8_t data_size, uint8_t repeated_start)
+{
+    // mbed uses 8-bit addresses, always confusing.
+    i2c.write(i2c_address<<1,(const char *)p_data,data_size,repeated_start);
+}
+
+
+void i2cRead(uint8_t i2c_address, uint8_t *p_data, uint8_t data_size)
+{
+    // mbed uses 8-bit addresses, always confusing.
+    i2c.read(i2c_address<<1,(char *)p_data,data_size);
+}
+
+
+// Not using BME280 SPI interface, provide stubs.
+void spiWrite(uint8_t *p_data, uint8_t data_size) {}
+void spiRead(uint8_t *p_data, uint8_t data_size) {}
+
+
+int main(void)
+{
+    led1 = LED_OFF;
+    led2 = LED_OFF;
+    led3 = LED_OFF;
+    
+    printf("Elektor project 150652\n");
+    printf("BME280 weather sensor\n");
+#if defined TARGET_LPC81X
+    printf("for LPC800-MAX\n");
+#elif defined TARGET_NRF51_MICROBIT
+    printf("for BBC micro:bit\n");
+#endif
+
+#if BME280_ALLOW_FLOAT!=0
+    printf("Using floating point maths\n");
+#else
+    printf("Using integer maths\n");
+#endif
+
+    if (bme280.begin(BME280_I2C_ADDRESS2)!=0)
+    {
+        printf("\n*** BME280 not found.\n");
+    }
+    printf("\n");
+    
+    // Configure for test purposes.
+    bme280.writeConfigRegister(BME280_STANDBY_500_US,BME280_FILTER_OFF,0);
+    bme280.writeControlRegisters(BME280_OVERSAMPLING_1X,BME280_OVERSAMPLING_1X,BME280_OVERSAMPLING_1X,BME280_MODE_NORMAL);
+
+    while (1)
+    {
+        led1 = LED_ON;
+ 
+        bme280.read();
+#if BME280_ALLOW_FLOAT!=0
+        printf("T=%0.1f degrees C, P=%0.1f mbar, RH=%0.1f%%\n",bme280.temperature(),bme280.pressure()/100,bme280.humidity());
+#else
+        printf("T=%d degrees C, P=%d mbar, RH=%d%%\n",bme280.temperature()/100,bme280.pressure()/100,bme280.humidity()>>10);
+#endif
+
+        // Worst case speed is about 1 Hz.
+        // Keep flash short, it is terribly bright.
+        wait_ms(5);
+        led1 = LED_OFF;
+        wait_ms(995);
+    }
+}

diff -r 000000000000 -r b16a9b34fa4c mbed.bld
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed.bld	Tue Sep 06 15:17:20 2016 +0000
@@ -0,0 +1,1 @@
+http://mbed.org/users/mbed_official/code/mbed/builds/165afa46840b
\ No newline at end of file