bme280

The BME280 is a great new chip which was originally designed for the next generation of smartphones. It is made up of a very accurate pressure sensor and an associated temperature sensor which helps calibrate the pressure readings.

And just for fun they threw in a pretty solid humidity sensor in there as well! So with an I2C connection you have access to enough weather data to make some pretty good predictions for your local area.

Or you can just use the pressure sensor with it’s abililty to discern the difference in 7.5cm in altitude.

The chip contains smarts to smooth out measurements

Connection:

vin—————-3v3
GND————–GND
SCL—————-21
SDA—————-20

arduino due and bme280

Code

No libraries required but a lot of code, there are libraries but I didn’t test these. This could quite easily be turned into a library

[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 and you should see readings like the following

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

Expect to pay around $3.30 for one of these from this link

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