Micro:bit and bme280 environmental sensor example

The BME280 is an integrated environmental sensor developed specifically for mobile applications where size and low power consumption are key design constraints. The unit combines individual high linearity, high accuracy sensors for pressure, humidity and temperature in an 8-pin metal-lid 2.5 x 2.5 x 0.93 mm³ LGA package, designed for low current consumption (3.6 μA @1Hz), long term stability and high EMC robustness.

The humidity sensor features an extremely fast response time which supports performance requirements for emerging applications such as context awareness, and high accuracy over a wide temperature range. The pressure sensor is an absolute barometric pressure sensor with features exceptionally high accuracy and resolution at very low noise. The integrated temperature sensor has been optimized for very low noise and high resolution. It is primarily used for temperature compensation of the pressure and humidity sensors, and can also be used for estimating ambient temperature.

The BME280 supports a full suite of operating modes which provides the flexibility to optimize the device for power consumption, resolution and filter performance.”

Applications

– Context awareness, e.g. skin detection, room change detection

– Fitness monitoring / well-being

– Warning regarding dryness or high temperatures

– Measurement of volume and air flow

– Home automation control

– Control heating, ventilation, air conditioning (HVAC)

– Internet of things

– GPS enhancement (e.g. time-to-first-fix improvement, dead reckoning, slope detection)

– Indoor navigation (change of floor detection, elevator detection)

– Outdoor navigation, leisure and sports applications

– Weather forecast

– Vertical velocity indication (rise/sink speed)

Connection

Code:

No libraries required

[codesyntax lang=”cpp”]

// Distributed with a free-will license.
// Use it any way you want, profit or free, provided it fits in the licenses of its associated works.
// BME280
// This code is designed to work with the BME280_I2CS I2C Mini Module available from ControlEverything.com.
// https://www.controleverything.com/content/Humidity?sku=BME280_I2CS#tabs-0-product_tabset-2

#include<Wire.h>

// BME280 I2C address is 0x76(108)
#define Addr 0x76

void setup()
{
// Initialise I2C communication as MASTER
Wire.begin();
// Initialise Serial communication, set baud rate = 9600
Serial.begin(9600);
}

void loop()
{
unsigned int b1[24];
unsigned int data[8];
unsigned int dig_H1 = 0;
for(int i = 0; i < 24; i++)
{
// Start I2C Transmission
Wire.beginTransmission(Addr);
// Select data register
Wire.write((136+i));
// Stop I2C Transmission
Wire.endTransmission();

// Request 1 byte of data
Wire.requestFrom(Addr, 1);

// Read 24 bytes of data
if(Wire.available() == 1)
{
b1[i] = Wire.read();
}
}

// Convert the data
// temp coefficients
unsigned int dig_T1 = (b1[0] & 0xff) + ((b1[1] & 0xff) * 256);
int dig_T2 = b1[2] + (b1[3] * 256);
int dig_T3 = b1[4] + (b1[5] * 256);

// pressure coefficients
unsigned int dig_P1 = (b1[6] & 0xff) + ((b1[7] & 0xff ) * 256);
int dig_P2 = b1[8] + (b1[9] * 256);
int dig_P3 = b1[10] + (b1[11] * 256);
int dig_P4 = b1[12] + (b1[13] * 256);
int dig_P5 = b1[14] + (b1[15] * 256);
int dig_P6 = b1[16] + (b1[17] * 256);
int dig_P7 = b1[18] + (b1[19] * 256);
int dig_P8 = b1[20] + (b1[21] * 256);
int dig_P9 = b1[22] + (b1[23] * 256);

// Start I2C Transmission
Wire.beginTransmission(Addr);
// Select data register
Wire.write(161);
// Stop I2C Transmission
Wire.endTransmission();

// Request 1 byte of data
Wire.requestFrom(Addr, 1);

// Read 1 byte of data
if(Wire.available() == 1)
{
dig_H1 = Wire.read();
}

for(int i = 0; i < 7; i++)
{
// Start I2C Transmission
Wire.beginTransmission(Addr);
// Select data register
Wire.write((225+i));
// Stop I2C Transmission
Wire.endTransmission();

// Request 1 byte of data
Wire.requestFrom(Addr, 1);

// Read 7 bytes of data
if(Wire.available() == 1)
{
b1[i] = Wire.read();
}
}

// Convert the data
// humidity coefficients
int dig_H2 = b1[0] + (b1[1] * 256);
unsigned int dig_H3 = b1[2] & 0xFF ;
int dig_H4 = (b1[3] * 16) + (b1[4] & 0xF);
int dig_H5 = (b1[4] / 16) + (b1[5] * 16);
int dig_H6 = b1[6];

// Start I2C Transmission
Wire.beginTransmission(Addr);
// Select control humidity register
Wire.write(0xF2);
// Humidity over sampling rate = 1
Wire.write(0x01);
// Stop I2C Transmission
Wire.endTransmission();

// Start I2C Transmission
Wire.beginTransmission(Addr);
// Select control measurement register
Wire.write(0xF4);
// Normal mode, temp and pressure over sampling rate = 1
Wire.write(0x27);
// Stop I2C Transmission
Wire.endTransmission();

// Start I2C Transmission
Wire.beginTransmission(Addr);
// Select config register
Wire.write(0xF5);
// Stand_by time = 1000ms
Wire.write(0xA0);
// Stop I2C Transmission
Wire.endTransmission();

for(int i = 0; i < 8; i++)
{
// Start I2C Transmission
Wire.beginTransmission(Addr);
// Select data register
Wire.write((247+i));
// Stop I2C Transmission
Wire.endTransmission();

// Request 1 byte of data
Wire.requestFrom(Addr, 1);

// Read 8 bytes of data
if(Wire.available() == 1)
{
data[i] = Wire.read();
}
}

// Convert pressure and temperature data to 19-bits
long adc_p = (((long)(data[0] & 0xFF) * 65536) + ((long)(data[1] & 0xFF) * 256) + (long)(data[2] & 0xF0)) / 16;
long adc_t = (((long)(data[3] & 0xFF) * 65536) + ((long)(data[4] & 0xFF) * 256) + (long)(data[5] & 0xF0)) / 16;
// Convert the humidity data
long adc_h = ((long)(data[6] & 0xFF) * 256 + (long)(data[7] & 0xFF));

// Temperature offset calculations
double var1 = (((double)adc_t) / 16384.0 - ((double)dig_T1) / 1024.0) * ((double)dig_T2);
double var2 = ((((double)adc_t) / 131072.0 - ((double)dig_T1) / 8192.0) *
(((double)adc_t)/131072.0 - ((double)dig_T1)/8192.0)) * ((double)dig_T3);
double t_fine = (long)(var1 + var2);
double cTemp = (var1 + var2) / 5120.0;
double fTemp = cTemp * 1.8 + 32;

// Pressure offset calculations
var1 = ((double)t_fine / 2.0) - 64000.0;
var2 = var1 * var1 * ((double)dig_P6) / 32768.0;
var2 = var2 + var1 * ((double)dig_P5) * 2.0;
var2 = (var2 / 4.0) + (((double)dig_P4) * 65536.0);
var1 = (((double) dig_P3) * var1 * var1 / 524288.0 + ((double) dig_P2) * var1) / 524288.0;
var1 = (1.0 + var1 / 32768.0) * ((double)dig_P1);
double p = 1048576.0 - (double)adc_p;
p = (p - (var2 / 4096.0)) * 6250.0 / var1;
var1 = ((double) dig_P9) * p * p / 2147483648.0;
var2 = p * ((double) dig_P8) / 32768.0;
double pressure = (p + (var1 + var2 + ((double)dig_P7)) / 16.0) / 100;

// Humidity offset calculations
double var_H = (((double)t_fine) - 76800.0);
var_H = (adc_h - (dig_H4 * 64.0 + dig_H5 / 16384.0 * var_H)) * (dig_H2 / 65536.0 * (1.0 + dig_H6 / 67108864.0 * var_H * (1.0 + dig_H3 / 67108864.0 * var_H)));
double humidity = var_H * (1.0 - dig_H1 * var_H / 524288.0);
if(humidity > 100.0)
{
humidity = 100.0;
}
else if(humidity < 0.0)
{
humidity = 0.0;
}

// Output data to serial monitor
Serial.print("Temperature in Celsius : ");
Serial.print(cTemp);
Serial.println(" C");
Serial.print("Temperature in Fahrenheit : ");
Serial.print(fTemp);
Serial.println(" F");
Serial.print("Pressure : ");
Serial.print(pressure);
Serial.println(" hPa");
Serial.print("Relative Humidity : ");
Serial.print(humidity);
Serial.println(" RH");
delay(1000);
}

[/codesyntax]

Output

In the serial monitor

Temperature in Celsius : 34.20 C
Temperature in Fahrenheit : 93.56 F
Pressure : 903.94 hPa
Relative Humidity : 0.00 RH
Temperature in Celsius : 34.51 C
Temperature in Fahrenheit : 94.11 F
Pressure : 893.48 hPa
Relative Humidity : 0.00 RH
Temperature in Celsius : 33.74 C
Temperature in Fahrenheit : 92.73 F
Pressure : 919.16 hPa
Relative Humidity : 0.00 RH

Links

BME280 Digital Sensor Temperature Humidity Barometric Pressure Sensor Module I2C SPI 1.8-5V