Bmp180 - Measuring pressure

⚠️

This library uses the char value to return error codes and delay values in the form of numbers. Although using the char data type may seem unintuitive when returning numbers, it is essentially an 8-bit unsigned integer.

To get pressure values, first begin a reading using the startPressure() function. Then, after a short delay, retrieve the value of that reading using the getPressure() function.

void loop() {
  double temperature;
  double pressure;
  /* Defines how accurate the measurement will be: 0 for fast but less accurate,
     and 3 for the most accurate but slowest */
  char pressure_oversampling = 0;
  // Start temperature reading
  char return_value_temperature = bmp180.startTemperature();
  // Start pressure reading
  char return_value_pressure = bmp180.startPressure(pressure_oversampling);
  // If the return value is 0, then the measurement failed
  if (return_value_temperature == 0)
  {
    Serial.println("Failed to get temperature reading from BMP180!");
  }
  else
  {
    /* If it succeeded, wait for a delay equal to the return value
       of the startTemperature() function before retrieving the temperature */
    delay(return_value_temperature);
    // Store the read value into the temperature variable
    bmp180.getTemperature(temperature);
  }
  // If the return value is 0, then the measurement failed
  if (return_value_pressure == 0)
  {
    Serial.println("Failed to get pressure reading from BMP180!");
  }
  else
  {
    /* If it succeeded, wait for a delay equal to the return value
       of the startPressure() function before retrieving the pressure */
    delay(return_value_pressure);

    bmp180.getPressure(pressure, temperature);

    Serial.println("Pressure: " + String(pressure) + " mBar");
  }

  // Take a measurement every 2s
  delay(2000);
}

Serial monitor

bmp180.startPressure(char oversampling)

Begins a pressure reading

Returns value: Char value; returns a nonzero value if the temperature was successfully read (this value should be used as a delay in ms before retrieving the measurement), and 0 if there was a problem communicating with the sensor. The delay duration is determined by the oversampling value.

Function parameters:

Type	Name	Description
char	oversampling	The degree of oversampling the sensor will take, ranging from 0 to 3. A higher number increases oversampling and the delay before reading the measurement.

bmp180.getPressure(double &P, double &T)

Retrieves a previously started pressure reading in absolute mBar

Returns value: Char value; returns 1 if data retrieval was successful and 0 otherwise.

Function parameters:

Type	Name	Description
double	P	Variable in which the pressure measurement will be stored
double	T	Previously calculated temperature reading

⚠️

Note that the calculated pressure value is in absolute mBar. To compensate for altitude, call the sealevel() function:

    bmp180.getPressure(pressure, temperature);
    // Altitude of our office in Osijek :)
    double altitude = 94;
    // Get the relative pressure by using the last pressure measurement and altitude
    double relative_pressure = bmp180.sealevel(pressure, altitude);

    Serial.println("Relative pressure: " + String(relative_pressure) + " mBar");

Serial monitor

bmp180.sealevel(double P, double A)

Calculates relative pressure based on the absolute pressure and the current altitude

Returns value: Double value representing the relative pressure in mBar

Function parameters:

Type	Name	Description
double	P	Absolute pressure value in mBar
double	A	Current altitude in meters