Ashley Mills / MMA8452

Library for driving the MMA8452 accelerometer over I2C

Dependents:   MMA8452_Test MMA8452_Demo Dualing_Tanks IMU-Controlled_MP3_Player ... more

Here is a simple example:

#include "mbed.h"
#include "MMA8452.h"

int main() {
   Serial pc(USBTX,USBRX);
   pc.baud(115200);
   double x = 0, y = 0, z = 0;

   MMA8452 acc(p28, p27, 40000);
   acc.setBitDepth(MMA8452::BIT_DEPTH_12);
   acc.setDynamicRange(MMA8452::DYNAMIC_RANGE_4G);
   acc.setDataRate(MMA8452::RATE_100);
   
   while(1) {
      if(!acc.isXYZReady()) {
         wait(0.01);
         continue;
      }
      acc.readXYZGravity(&x,&y,&z);
      pc.printf("Gravities: %lf %lf %lf\r\n",x,y,z);
   }
}

An easy way to test that this actually works is to run the loop above and hold the MMA8452 parallel to the ground along the respective axis (and upsidedown in each axis). You will see 1G on the respective axis and 0G on the others.

Diff: MMA8452.cpp

Revision:
20:d55e9d7eb17e
Parent:
19:4d6cd7140a71
Child:
21:a92a632a0cc7
diff -r 4d6cd7140a71 -r d55e9d7eb17e MMA8452.cpp
--- a/MMA8452.cpp	Thu Mar 06 18:07:43 2014 +0000
+++ b/MMA8452.cpp	Fri Mar 07 11:55:30 2014 +0000
@@ -244,34 +244,51 @@
    return 0;
 }
 
-int readXCount(int *x) {
+int MMA8452::readXCount(int *x) {
    char buf[2];
    if(readXRaw((char*)&buf)) {
        return 1;
    }
    if(_bitDepth==BIT_DEPTH_12) {
      *x = twelveBitToSigned(&buf[0]);
-     *y = twelveBitToSigned(&buf[2]);
-     *z = twelveBitToSigned(&buf[4]);
    } else {
      *x = eightBitToSigned(&buf[0]);
-     *y = eightBitToSigned(&buf[1]);
-     *z = eightBitToSigned(&buf[2]);
+   }
+   return 0;
+}
+
+int MMA8452::readYCount(int *y) {
+   char buf[2];
+   if(readYRaw((char*)&buf)) {
+       return 1;
+   }
+   if(_bitDepth==BIT_DEPTH_12) {
+     *y = twelveBitToSigned(&buf[0]);
+   } else {
+     *y = eightBitToSigned(&buf[0]);
    }
-   
+   return 0;
+}
+
+int MMA8452::readZCount(int *z) {
+   char buf[2];
+   if(readZRaw((char*)&buf)) {
+       return 1;
+   }
+   if(_bitDepth==BIT_DEPTH_12) {
+     *z = twelveBitToSigned(&buf[0]);
+   } else {
+     *z = eightBitToSigned(&buf[0]);
+   }
+   return 0;
 }
 
 double MMA8452::convertCountToGravity(int count, int countsPerG) {
    return (double)count/(double)countsPerG;
 }
 
-int MMA8452::readXYZGravity(double *x, double *y, double *z) {
-   int xCount = 0, yCount = 0, zCount = 0;
-   if(readXYZCounts(&xCount,&yCount,&zCount)) {
-      return 1;
-   }
-   
-   // assume starting with DYNAMIC_RANGE_2G and BIT_DEPTH_12
+int MMA8452::getCountsPerG() {
+ // assume starting with DYNAMIC_RANGE_2G and BIT_DEPTH_12
    int countsPerG = 1024;
    if(_bitDepth==BIT_DEPTH_8) {
       countsPerG = 64;
@@ -284,6 +301,15 @@
          countsPerG /= 4;
       break;
    }
+   return countsPerG;
+}
+
+int MMA8452::readXYZGravity(double *x, double *y, double *z) {
+   int xCount = 0, yCount = 0, zCount = 0;
+   if(readXYZCounts(&xCount,&yCount,&zCount)) {
+      return 1;
+   }
+   int countsPerG = getCountsPerG();
    
    *x = convertCountToGravity(xCount,countsPerG);
    *y = convertCountToGravity(yCount,countsPerG);
@@ -291,6 +317,39 @@
    return 0;
 }
 
+int MMA8452::readXGravity(double *x) {
+   int xCount = 0;
+   if(readXCount(&xCount)) {
+      return 1;
+   }
+   int countsPerG = getCountsPerG();
+   
+   *x = convertCountToGravity(xCount,countsPerG);
+   return 0;
+}
+
+int MMA8452::readYGravity(double *y) {
+   int yCount = 0;
+   if(readYCount(&yCount)) {
+      return 1;
+   }
+   int countsPerG = getCountsPerG();
+   
+   *y = convertCountToGravity(yCount,countsPerG);
+   return 0;
+}
+
+int MMA8452::readZGravity(double *z) {
+   int zCount = 0;
+   if(readZCount(&zCount)) {
+      return 1;
+   }
+   int countsPerG = getCountsPerG();
+   
+   *z = convertCountToGravity(zCount,countsPerG);
+   return 0;
+}
+
 // apply an AND mask to a register. read register value, apply mask, write it back
 int MMA8452::logicalANDRegister(char addr, char mask) {
    char value = 0;