AccelSensor.cpp

00001 #include "mbed.h"
00002 #include "AccelSensor.h"
00003 
00004 AccelSensor::AccelSensor(PinName sda, PinName scl) : _i2c(sda, scl) {
00005     //No need to initialise anything else.
00006 }
00007 
00008 void AccelSensor::init() {
00009     char c = readRegister(WHO_AM_I); // Read WHO_AM_I register
00010     standby(); // Must be in standby to change registers
00011     char scale = GSCALE; // Set up the full scale range to 2, 4, or 8g.
00012     if (scale > 8) scale = 8; //Easy error check
00013     scale >>= 2; // Neat trick, see page 22. 00 = 2G, 01 = 4G, 10 = 8G
00014     writeRegister(XYZ_DATA_CFG, scale);
00015     active(); // Set to active to start reading
00016 }
00017 
00018 void AccelSensor::standby() {
00019     char c = readRegister(CTRL_REG1);
00020     writeRegister(CTRL_REG1, c & ~(0x01)); //Clear the active bit to go into standby
00021 }
00022 
00023 void AccelSensor::active() {
00024     char c = readRegister(CTRL_REG1);
00025     writeRegister(CTRL_REG1, c | 0x01); //Set the active bit to begin detection
00026 }
00027 
00028 void AccelSensor::readData(int *destination) {
00029     char rawData[6]; // x/y/z accel register data stored here
00030     readRegisters(OUT_X_MSB, 6, rawData); // Read the six raw data registers into data array
00031     // Loop to calculate 12-bit ADC and g value for each axis
00032     for(int i = 0; i < 3 ; i++) {
00033         int value = (rawData[i*2] << 8) | rawData[(i*2)+1]; //Combine the two 8 bit registers into one 12-bit number
00034         value >>= 4; //The registers are left align, here we right align the 12-bit integer
00035         // If the number is negative, we have to make it so manually (no 12-bit data type)
00036         if (rawData[i*2] > 0x7F) {
00037             value |= 0xFFFFF << 12;
00038         }
00039         destination[i] = value;
00040     }
00041 }
00042 
00043 void AccelSensor::readRegisters(char reg, int range, char* dest) {
00044     int ack = 0;
00045     _i2c.start();
00046     ack = _i2c.write((ADDRESS << 1));
00047     ack = _i2c.write(reg);
00048     _i2c.start();
00049     ack = _i2c.write((ADDRESS << 1) | 0x01);
00050     for (int i = 0; i < range - 1; i++) dest[i] = _i2c.read(1);
00051     dest[range - 1] = _i2c.read(0);
00052     _i2c.stop();
00053 }
00054 
00055 char AccelSensor::readRegister(char reg) {
00056     int ack = 0;
00057     _i2c.start();
00058     ack = _i2c.write((ADDRESS << 1));
00059     ack = _i2c.write(reg);
00060     _i2c.start();
00061     ack = _i2c.write((ADDRESS << 1) | 0x01);
00062     char result = _i2c.read(0);
00063     _i2c.stop();
00064     return result;
00065 }
00066 
00067 void AccelSensor::writeRegister(char reg, char data) {
00068     int ack = 0;
00069     _i2c.start();
00070     ack = _i2c.write((ADDRESS << 1));
00071     ack = _i2c.write(reg);
00072     ack = _i2c.write(data);
00073     _i2c.stop();
00074 }