Your sketch must #include this library, and the Wire library. (Wire is a standard library included with Arduino.):

#include <SFE_BMP180.h> #include <Wire.h>

You will need to create an SFE_BMP180 object, here called “pressure”: SFE_BMP180 pressure; double baseline; baseline pressure

void setup() {

Serial.begin(9600);
Serial.println("REBOOT");

// Initialize the sensor (it is important to get calibration values stored on the device).

if (pressure.begin())
  Serial.println("BMP180 init success");
else
{
  // Oops, something went wrong, this is usually a connection problem,
  // see the comments at the top of this sketch for the proper connections.

  Serial.println("BMP180 init fail (disconnected?)\n\n");
  while(1); // Pause forever.
}

// Get the baseline pressure:

baseline = getPressure();

Serial.print("baseline pressure: ");
Serial.print(baseline);
Serial.println(" mb");  

}

void loop() {

double a,P;

// Get a new pressure reading:

P = getPressure();
Serial.println(P);
// Show the relative altitude difference between
// the new reading and the baseline reading:

a = pressure.altitude(P,baseline);

Serial.print("relative altitude: ");
if (a >= 0.0) Serial.print(" "); // add a space for positive numbers
Serial.print(a,1);
Serial.print(" meters, ");
if (a >= 0.0) Serial.print(" "); // add a space for positive numbers
Serial.print(a*3.28084,0);
Serial.println(" feet");

delay(500);

}

double getPressure() {

char status;
double T,P,p0,a;

// You must first get a temperature measurement to perform a pressure reading.

// Start a temperature measurement:
// If request is successful, the number of ms to wait is returned.
// If request is unsuccessful, 0 is returned.

status = pressure.startTemperature();
if (status != 0)
{
  // Wait for the measurement to complete:

  delay(status);

  // Retrieve the completed temperature measurement:
  // Note that the measurement is stored in the variable T.
  // Use '&T' to provide the address of T to the function.
  // Function returns 1 if successful, 0 if failure.

  status = pressure.getTemperature(T);
  if (status != 0)
  {
    // Start a pressure measurement:
    // The parameter is the oversampling setting, from 0 to 3 (highest res, longest wait).
    // If request is successful, the number of ms to wait is returned.
    // If request is unsuccessful, 0 is returned.

    status = pressure.startPressure(3);
    if (status != 0)
    {
      // Wait for the measurement to complete:
      delay(status);

      // Retrieve the completed pressure measurement:
      // Note that the measurement is stored in the variable P.
      // Use '&P' to provide the address of P.
      // Note also that the function requires the previous temperature measurement (T).
      // (If temperature is stable, you can do one temperature measurement for a number of pressure measurements.)
      // Function returns 1 if successful, 0 if failure.

      status = pressure.getPressure(P,T);
      if (status != 0)
      {
        return(P);
      }
      else Serial.println("error retrieving pressure measurement\n");
    }
    else Serial.println("error starting pressure measurement\n");
  }
  else Serial.println("error retrieving temperature measurement\n");
}
else Serial.println("error starting temperature measurement\n");

}

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