ADXL345.cpp

00001 #include "ADXL345.h"
00002 
00003 ADXL345::ADXL345(PinName sda, PinName scl) : I2C_Sensor(sda, scl, ADXL345_I2C_ADDRESS)
00004 {
00005     #warning these three offsets are calibration values to make shure the measurement is 0 when no acceleration is present
00006     offset[0] = -9.1; // offset calculated by hand... (min + ((max - min) / 2)
00007     offset[1] = -7.1; // TODO: make this automatic with saving to filesystem
00008     offset[2] = 6;
00009     
00010     // Set Offset  - programmed into the OFSX, OFSY, and OFXZ registers, respectively, as 0xFD, 0x03 and 0xFE.
00011     writeRegister(ADXL345_OFSX_REG, 0xFA); // to get these offsets just lie your sensor down on the table always the axis pointing down to earth has 200+ and the others should have more or less 0
00012     writeRegister(ADXL345_OFSY_REG, 0xFE);
00013     writeRegister(ADXL345_OFSZ_REG, 0x0A);
00014  
00015     writeRegister(ADXL345_BW_RATE_REG, 0x0F); // 3200Hz BW-Rate
00016     writeRegister(ADXL345_DATA_FORMAT_REG, 0x0B); // set data format to full resolution and +-16g
00017     writeRegister(ADXL345_POWER_CTL_REG, 0x08); // set mode
00018 }
00019 
00020 void ADXL345::read(){
00021     readraw();
00022     for (int i = 0; i < 3; i++)
00023         data[i] = raw[i] - offset[i]; // TODO: didnt care about units 
00024 }
00025 
00026 void ADXL345::readraw(){
00027     char buffer[6];    
00028     readMultiRegister(ADXL345_DATAX0_REG, buffer, 6);
00029     
00030     raw[0] = (short) ((int)buffer[1] << 8 | (int)buffer[0]);
00031     raw[1] = (short) ((int)buffer[3] << 8 | (int)buffer[2]);
00032     raw[2] = (short) ((int)buffer[5] << 8 | (int)buffer[4]);
00033 }
00034 
00035 void ADXL345::calibrate(int times, float separation_time)
00036 {
00037     // calibrate sensor with an average of count samples (result of calibration stored in offset[])
00038     float calib[3] = {0,0,0};                           // temporary array for the sum of calibration measurement
00039     
00040     for (int j = 0; j < times; j++) {                   // read 'times' times the data in a very short time
00041         readraw();
00042         for (int i = 0; i < 3; i++)
00043             calib[i] += raw[i];
00044         wait(separation_time);
00045     }
00046     
00047     for (int i = 0; i < 3; i++)
00048         offset[i] = calib[i]/times;                     // take the average of the calibration measurements
00049 }