Revision 0:7dd118f48b1b, committed 2012-12-06

Comitter:

dagronlund

Date:

Thu Dec 06 17:50:14 2012 +0000

Commit message:

First revision of mBed library for the Triple Axis Accelerometer Breakout - MMA8452Q from Sparkfun.

Changed in this revision

diff -r 000000000000 -r 7dd118f48b1b AccelSensor.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/AccelSensor.cpp	Thu Dec 06 17:50:14 2012 +0000
@@ -0,0 +1,74 @@
+#include "mbed.h"
+#include "AccelSensor.h"
+
+AccelSensor::AccelSensor(PinName sda, PinName scl) : _i2c(sda, scl) {
+    //No need to initialise anything else.
+}
+
+void AccelSensor::init() {
+    char c = readRegister(WHO_AM_I); // Read WHO_AM_I register
+    standby(); // Must be in standby to change registers
+    char scale = GSCALE; // Set up the full scale range to 2, 4, or 8g.
+    if (scale > 8) scale = 8; //Easy error check
+    scale >>= 2; // Neat trick, see page 22. 00 = 2G, 01 = 4G, 10 = 8G
+    writeRegister(XYZ_DATA_CFG, scale);
+    active(); // Set to active to start reading
+}
+
+void AccelSensor::standby() {
+    char c = readRegister(CTRL_REG1);
+    writeRegister(CTRL_REG1, c & ~(0x01)); //Clear the active bit to go into standby
+}
+
+void AccelSensor::active() {
+    char c = readRegister(CTRL_REG1);
+    writeRegister(CTRL_REG1, c | 0x01); //Set the active bit to begin detection
+}
+
+void AccelSensor::readData(int *destination) {
+    char rawData[6]; // x/y/z accel register data stored here
+    readRegisters(OUT_X_MSB, 6, rawData); // Read the six raw data registers into data array
+    // Loop to calculate 12-bit ADC and g value for each axis
+    for(int i = 0; i < 3 ; i++) {
+        int value = (rawData[i*2] << 8) | rawData[(i*2)+1]; //Combine the two 8 bit registers into one 12-bit number
+        value >>= 4; //The registers are left align, here we right align the 12-bit integer
+        // If the number is negative, we have to make it so manually (no 12-bit data type)
+        if (rawData[i*2] > 0x7F) {
+            value |= 0xFFFFF << 12;
+        }
+        destination[i] = value;
+    }
+}
+
+void AccelSensor::readRegisters(char reg, int range, char* dest) {
+    int ack = 0;
+    _i2c.start();
+    ack = _i2c.write((ADDRESS << 1));
+    ack = _i2c.write(reg);
+    _i2c.start();
+    ack = _i2c.write((ADDRESS << 1) | 0x01);
+    for (int i = 0; i < range - 1; i++) dest[i] = _i2c.read(1);
+    dest[range - 1] = _i2c.read(0);
+    _i2c.stop();
+}
+
+char AccelSensor::readRegister(char reg) {
+    int ack = 0;
+    _i2c.start();
+    ack = _i2c.write((ADDRESS << 1));
+    ack = _i2c.write(reg);
+    _i2c.start();
+    ack = _i2c.write((ADDRESS << 1) | 0x01);
+    char result = _i2c.read(0);
+    _i2c.stop();
+    return result;
+}
+
+void AccelSensor::writeRegister(char reg, char data) {
+    int ack = 0;
+    _i2c.start();
+    ack = _i2c.write((ADDRESS << 1));
+    ack = _i2c.write(reg);
+    ack = _i2c.write(data);
+    _i2c.stop();
+}
\ No newline at end of file

diff -r 000000000000 -r 7dd118f48b1b AccelSensor.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/AccelSensor.h	Thu Dec 06 17:50:14 2012 +0000
@@ -0,0 +1,33 @@
+#ifndef MBED_NOKIALCD_H
+#define MBED_NOKIALCD_H
+
+#include "mbed.h"
+
+//http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Sensors/Accelerometers/MMA8452Q.pdf
+//http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Sensors/Accelerometers/MMA8452Q-Breakout-v11-fixed.pdf
+//http://cache.freescale.com/files/sensors/doc/app_note/AN4069.pdf
+
+// The SparkFun breakout board defaults to 1, set to 0 if SA0 jumper on the bottom of the board is set
+#define ADDRESS 0x1D // 0x1D if SA0 is high, 0x1C if low
+//Define a few of the registers that we will be accessing on the MMA8452
+#define OUT_X_MSB 0x01 //1
+#define XYZ_DATA_CFG 0x0E //14
+#define WHO_AM_I 0x0D //13
+#define CTRL_REG1 0x2A //42
+#define GSCALE 2 // Sets full-scale range to +/-2, 4, or 8g. Used to calc real g values.
+
+class AccelSensor {
+public:
+    AccelSensor(PinName sda, PinName scl);
+    void active();
+    void standby();
+    void init();
+    void readData(int *destination);
+private:
+    void readRegisters(char reg, int range, char* dest);
+    char readRegister(char reg);
+    void writeRegister(char reg, char data);
+    I2C _i2c;
+};
+
+#endif
\ No newline at end of file