Faster Readings With BMP180 I2C Sensor

I have a BMP180 barometric pressure sensor on an I2C breakout board connected to an Arduino. My goal is to use it for a model rocket altimeter. For that I need fast readings, ideally about 50 per second, or 20 mS between readings. With the example code below the fastest I’m able to get is about 20 readings per second, about 50 mS. Is there any way that the readings can be taken at a faster rate or is this the max for this sensor?

/* SFE_BMP180 altitude example sketch

This sketch shows how to use the Bosch BMP180 pressure sensor
as an altimiter.
https://www.sparkfun.com/products/11824

Like most pressure sensors, the BMP180 measures absolute pressure.
Since absolute pressure varies with altitude, you can use the pressure
to determine your altitude.

Because pressure also varies with weather, you must first take a pressure
reading at a known baseline altitude. Then you can measure variations
from that pressure

Hardware connections:

- (GND) to GND
+ (VDD) to 3.3V

(WARNING: do not connect + to 5V or the sensor will be damaged!)

You will also need to connect the I2C pins (SCL and SDA) to your
Arduino. The pins are different on different Arduinos:

Any Arduino pins labeled:  SDA  SCL
Uno, Redboard, Pro:        A4   A5
Mega2560, Due:             20   21
Leonardo:                   2    3

Leave the IO (VDDIO) pin unconnected. This pin is for connecting
the BMP180 to systems with lower logic levels such as 1.8V

Have fun! -Your friends at SparkFun.

The SFE_BMP180 library uses floating-point equations developed by the
Weather Station Data Logger project: http://wmrx00.sourceforge.net/

Our example code uses the "beerware" license. You can do anything
you like with this code. No really, anything. If you find it useful,
buy me a beer someday.

V10 Mike Grusin, SparkFun Electronics 10/24/2013
V1.1.2 Updates for Arduino 1.6.4 5/2015
*/

// 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();

  // 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.print(" feet  ");
  Serial.println(millis());
  delay(0);
}


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");
}

You can speed up the 100kHz I2C clock . (to at least to 400 kHz)
have a look
also read BMPs datasheet : @3.4MHz conversion time 7.5ms for pressure (+ 4.5ms for temp)

Thanks for the suggestion. I went into the wire library and changed the clock speed to 400kHz, and it did have a slight effect, but it only took a couple milliseconds off the time. If it has a 7.5+4.5 mS conversion time, it should have a max of about 83 readings per second, but the best I am able to get is about 32. I did change the code somewhat, so I’ll repost it below. If you have any more suggestions I’d love to hear them.

// This is the example for the customized SFE_BMP180B library
// The result of the new library is only a few mS faster readings
// This sketch attempts to maximize the speed of readings
//The with everything - 3350 mS per 100 readings or 33.5 mS per reading
//The with only FT recorded - 3272 mS per 100 or 32.7 mS per reading
// using array and measuring then printing - 3233 mS per 100 or 32.3 mS per reading
/* SFE_BMP180 altitude example sketch

This sketch shows how to use the Bosch BMP180 pressure sensor
as an altimiter.
https://www.sparkfun.com/products/11824

Like most pressure sensors, the BMP180 measures absolute pressure.
Since absolute pressure varies with altitude, you can use the pressure
to determine your altitude.

Because pressure also varies with weather, you must first take a pressure
reading at a known baseline altitude. Then you can measure variations
from that pressure

Hardware connections:

- (GND) to GND
+ (VDD) to 3.3V

(WARNING: do not connect + to 5V or the sensor will be damaged!)

You will also need to connect the I2C pins (SCL and SDA) to your
Arduino. The pins are different on different Arduinos:

Any Arduino pins labeled:  SDA  SCL
Uno, Redboard, Pro:        A4   A5
Mega2560, Due:             20   21
Leonardo:                   2    3

Leave the IO (VDDIO) pin unconnected. This pin is for connecting
the BMP180 to systems with lower logic levels such as 1.8V

Have fun! -Your friends at SparkFun.

The SFE_BMP180 library uses floating-point equations developed by the
Weather Station Data Logger project: http://wmrx00.sourceforge.net/

Our example code uses the "beerware" license. You can do anything
you like with this code. No really, anything. If you find it useful,
buy me a beer someday.

V10 Mike Grusin, SparkFun Electronics 10/24/2013
V1.1.2 Updates for Arduino 1.6.4 5/2015
*/

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

#include <SFE_BMP180B.h>
#include <Wire.h>

// You will need to create an SFE_BMP180 object, here called "pressure":

SFE_BMP180B pressure;

double baseline; // baseline pressure
long initial;
int val[600];

void setup()
{
  Serial.begin(115200);
  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()
{
    initial = millis();

  for(int i = 0; i  < 600; i++) {
  double a,P;
  
  // Get a new pressure reading:

  P = getPressure();

  // Show the relative altitude difference between
  // the new reading and the baseline reading:

  a = pressure.altitude(P,baseline);
  val[i] = a*3.28084;
  
 // val[i] = 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.print(" feet   ");
 // Serial.print(i);
//  Serial.print("  ");
 // Serial.println(millis() - initial);
 }
 long time = millis() - initial;
for(byte i = 0; i < 30; i++) {
  for(byte j = 0; j < 20; j++) {
  Serial.print(val[(i*20) + j]);
  Serial.print(" ");
 }
 Serial.println();
}
Serial.println(time);
 delay(10000);
}


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");
}

Alter sensors internal parameters. Speed vs precision..
..also try 1 MHz