Michael Lange / MPL3115A2

Library to wrapper most of the functions on the MPL3115A2 pressure and temperature sensor.

Dependents:   WeatherBalloon4180 WeatherBalloon4180 mbed_rifletool Smart_Watch_4180_Final_Design ... more

MPL3115A2 Precision Altimeter

This class wraps the functions of the MPL3115A2 sensor into a usable class that exposes most functions to your project. Functions that are not exposed can easily be added using the existing functions in this library. Specifically, I did not add any functions to handle FIFO logging or the use of either of the pin interrupts. This should not be too difficult to add if you need those features.

The motivation here was to get a set of support classes together that supported the chip and could be expanded on. With this library you can extract all relevant data from the sensor.

Be sure to download the DATASHEET and the App Note AN4519.

This library was created using the mbed NXP LPC11U24. Pins p27 and p28 were used for the I2C functions. Be sure to install 1K pull-up resistors on both lines. Also, if you're not using the SparkFun breakout board, be sure to use the right caps on the power pin. If you don't, the jitter can cause problems.

This library was inspired by the similar library available for the Arduino written by Nathan Seidle at SparkFun. I copied some of the number crunching routines and tried to follow his style of coding for the library. That way users of Arduinos could step into this library a little easier.

Below is some sample code that outputs the sensor data to a serial debug terminal window. If you have a logic analyzer, like the Saleae Logic, then you might not need the debug terminal window. If you still need the serial driver for your mbed, you can get it here.

Sample Code

#include "mbed.h"
#include "MPL3115A2.h"

I2C i2c(p28, p27);       // sda, scl

// Comment out all of the references to 'pc' on this page if you don't have the 
// serial debug driver for your mbed board installed on your computer. If you do,
// I personally like to use Putty as the terminal window to capture debug messages.
Serial pc(USBTX, USBRX); // tx, rx

// Again, remove the '&pc' parameter is you're not debugging.
MPL3115A2 sensor(&i2c, &pc);

DigitalOut myled(LED1);     // Sanity check to make sure the program is working.
DigitalOut powerPin(p21);   // <-- I powered the sensor from a pin. You don't have to.

int main() {
    
    powerPin = 1;
    wait_ms(300);

    pc.printf("** MPL3115A2 SENSOR **\r\n");

    sensor.init();

    pc.printf("Who Am I: 0x%X\r\n", sensor.whoAmI());

    Altitude a;
    Temperature t;
    Pressure p;
    
    // Offsets for Dacula, GA
    sensor.setOffsetAltitude(83);
    sensor.setOffsetTemperature(20);
    sensor.setOffsetPressure(-32);
    
    while(1) 
    {
        sensor.readAltitude(&a);
        sensor.readTemperature(&t);
        
        sensor.setModeStandby();
        sensor.setModeBarometer();
        sensor.setModeActive();
        sensor.readPressure(&p);
        
        pc.printf("Altitude: %sft, Temp: %sºF, Pressure: %sPa\r\n", a.print(), t.print(), p.print());
        pc.printf("OFF_H: 0x%X, OFF_T: 0x%X, OFF_P: 0x%X\r\n", sensor.offsetAltitude(), sensor.offsetTemperature(), sensor.offsetPressure());
    
        myled = 1;
        wait(5);
        myled = 0;
        wait(5);

        sensor.setModeStandby();
        sensor.setModeAltimeter();
        sensor.setModeActive();
    }
}

Diff: MPL3115A2.h

Revision:
3:7c7c1ea6fc33
Parent:
2:2ebc9c0d4a54
--- a/MPL3115A2.h	Wed Apr 02 12:22:45 2014 +0000
+++ b/MPL3115A2.h	Wed Apr 02 12:59:44 2014 +0000
@@ -105,19 +105,32 @@
 {
 public:
     //! Constructs an MPL3115A2 object and associates an I2C and optional Serial debug object.
+    //! @param *i2c The I2C object to use for the sensor.
+    //! @param *pc An optional serial debug connection object.
     MPL3115A2(I2C *i2c, Serial *pc = NULL);
 
-    //! Call from main to initialize the sensor, defaulting to Altitude mode.
+    //! Initializes the sensor, defaulting to Altitude mode. This should be called before using
+    //! the sensor for the first time.
     void init();
 
-    //! Returns the fixed device ID number (usually equal to 0xC4).
+    //! Queries the value from the WHO_AM_I register (usually equal to 0xC4).
+    //! @return The fixed device ID from the sensor.
     char  whoAmI() { return i2cRead(WHO_AM_I); } 
     
-    //! Returns the passed in altitude object with altitude data.
+    //! Reads Altitude data from the sensor and returns it in the Altitude object passed in. If
+    //! no data could be read, the Altitude object is left as is.
+    //! @param a A pointer to an Altitude object that will receive the sensor data.
+    //! @returns The Altitude pointer that was passed in.
     Altitude* readAltitude(Altitude* a);            
-    //! Returns the passed in pressure object with barometric pressure data.
+    //! Reads Pressure data from the sensor and returns it in the Pressure object passed in. If
+    //! no data could be read, the Pressure object is left as is.
+    //! @param a A pointer to a Pressure object that will receive the sensor data.
+    //! @returns The Pressure pointer that was passed in.
     Pressure* readPressure(Pressure* p);            
-    //! Returns the passed in temperature object with temperature data.
+    //! Reads Temperature data from the sensor and returns it in the Temperature object passed in. If
+    //! no data could be read, the Temperature object is left as is.
+    //! @param a A pointer to an Temperature object that will receive the sensor data.
+    //! @returns The Temperature pointer that was passed in.
     Temperature* readTemperature(Temperature* t);
     
     // Use these methods to set the sensor's offsets to increase its accuracy. You can generally
@@ -126,6 +139,7 @@
     // pressure from the web for your area is generally not close enough to help with calibration.
     // You may need to play with the setting to achieve good accuracy. I found the offset steps
     // were not 100% accurate to the datasheet and had to adjust accordingly. 
+    
     //! Returns the altitude offset stored in the sensor.
     char offsetAltitude() { return i2cRead(OFF_H); }
     //! Sets the altitude offset stored in the sensor. The allowed offset range is from -128 to 127 meters.