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.

#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();
    }
}

--- a/Pressure.h	Wed Apr 02 12:22:45 2014 +0000
+++ b/Pressure.h	Wed Apr 02 12:59:44 2014 +0000
@@ -14,11 +14,17 @@
 
 #include "mbed.h"
 
+//! Pressure provides a wrapper around barometric data coming from the sensor. The class handles
+//! working with compressed data from the sensor and provides convenient functions for retreiving
+//! the data in various units (with room to add more if needed).
 class Pressure
 {
 public:
 
+    //! The size of the compressed data buffer from the sensor. Used in an I2C read.
     static const int size = 3;
+
+    //! The units we support converting the sensor data to.
     enum unitsType { PASCALS, PSI, INHG, MMHG };
 
     Pressure();
@@ -26,15 +32,19 @@
     Pressure(const char* compressed);
     Pressure(const char msb, const char csb, const char lsb);
 
+    //! Allows using the object directly in an I2C read operation.
     operator char*(void) { return _compressed; }
+    //! Same as calling pressure with PASCALS as the parameter.
     operator float(void) { return _pressure; }
 
     float pressure(unitsType units = PASCALS);
+    //! Call to decompress the sensor data after an I2C read.
     void setPressure();
     void setPressure(const char* compressed);
     void setPressure(const char msb, const char csb, const char lsb);
     void setPressure(float a, unitsType units = PASCALS);
 
+    //! Returns the pressure as a string in the units specified, defaulting to PASCAL if none specified.
     const char* print(unitsType units = PASCALS);
     
 private: