FXOS8700CQ.cpp

00001 /* FXOS8700CQ Library
00002 
00003 Sample code from ELEC2645 - demonstrates how to create a library
00004 for the K64F on-board accelerometer and magnetometer
00005 
00006 (c) Craig A. Evans, University of Leeds, Jan 2017
00007 
00008 */ 
00009 
00010 #include "FXOS8700CQ.h"
00011 #include <cmath>
00012 // constructor is called when the object is created - use it to set pins and frequency
00013 FXOS8700CQ::FXOS8700CQ(PinName sda, PinName scl)
00014 {
00015     i2c = new I2C(sda,scl);        // create new I2C instance and initialise
00016 }
00017 
00018 // destructor is called when the object goes out of scope
00019 FXOS8700CQ::~FXOS8700CQ()
00020 {
00021     delete i2c;        // free memory
00022 }
00023 
00024 // based on 13.4 in datasheet - 200 Hz hybrid mode (both acc and mag)
00025 void FXOS8700CQ::init()
00026 {
00027     // i2c fast-mode - 10.1.1 data sheet
00028     i2c->frequency(400000);       // I2C Fast Mode - 400kHz
00029 
00030     // the device has an ID number so we check the value to ensure the correct
00031     // drive is on the i2c bus
00032     char data = read_byte_from_reg(FXOS8700CQ_WHO_AM_I);
00033     if (data != FXOS8700CQ_WHO_AM_I_VAL) { // if correct ID not found, hang and flash error message
00034         error("Incorrect ID!");
00035     }
00036 
00037     // write 0000 0000 = 0x00 to accelerometer control register 1 to place
00038     // FXOS8700CQ into standby
00039     // [7-1] = 0000 000
00040     // [0]: active=0
00041     data = 0x00;
00042     send_byte_to_reg(data,FXOS8700CQ_CTRL_REG1);
00043 
00044     // write 0001 1111 = 0x1F to magnetometer control register 1
00045     // [7]: m_acal=0: auto calibration disabled
00046     // [6]: m_rst=0: no one-shot magnetic reset
00047     // [5]: m_ost=0: no one-shot magnetic measurement
00048     // [4-2]: m_os=111=7: 8x oversampling (for 200Hz) to reduce magnetometer noise
00049     // [1-0]: m_hms=11=3: select hybrid mode with accel and magnetometer active
00050     data = 0x1F;
00051     send_byte_to_reg(data,FXOS8700CQ_M_CTRL_REG1);
00052 
00053     // write 0010 0000 = 0x20 to magnetometer control register 2
00054     // [7]: reserved
00055     // [6]: reserved
00056     // [5]: hyb_autoinc_mode=1 to map the magnetometer registers to follow
00057     // the accelerometer registers
00058     // [4]: m_maxmin_dis=0 to retain default min/max latching even though not used
00059     // [3]: m_maxmin_dis_ths=0
00060     // [2]: m_maxmin_rst=0
00061     // [1-0]: m_rst_cnt=00 to enable magnetic reset each cycle
00062     data = 0x20;
00063     send_byte_to_reg(data,FXOS8700CQ_M_CTRL_REG2);
00064 
00065     // write 0000 0001= 0x01 to XYZ_DATA_CFG register
00066     // [7]: reserved
00067     // [6]: reserved
00068     // [5]: reserved
00069     // [4]: hpf_out=0
00070     // [3]: reserved
00071     // [2]: reserved
00072     // [1-0]: fs=01 for accelerometer range of +/-4g range with 0.488mg/LSB
00073     data = 0x01;
00074     send_byte_to_reg(data,FXOS8700CQ_XYZ_DATA_CFG);
00075 
00076     // write 0000 1101 = 0x0D to accelerometer control register 1
00077     // [7-6]: aslp_rate=00
00078     // [5-3]: dr=001 for 200Hz data rate (when in hybrid mode)
00079     // [2]: lnoise=1 for low noise mode
00080     // [1]: f_read=0 for normal 16 bit reads
00081     // [0]: active=1 to take the part out of standby and enable sampling
00082     data = 0x0D;
00083     send_byte_to_reg(data,FXOS8700CQ_CTRL_REG1);
00084 
00085 }
00086 
00087 Data FXOS8700CQ::get_values()
00088 {
00089     // 13 bytes - status plus 6 channels (2 bytes each)
00090     // x,y,z for accelerometer and magnetometer
00091     char data[FXOS8700CQ_READ_LEN];
00092     read_bytes_from_reg(FXOS8700CQ_STATUS,FXOS8700CQ_READ_LEN,data);
00093 
00094     // copy the 14 bit accelerometer byte data into 16 bit words
00095     int acc_x = (int16_t)(((data[1] << 8) | data[2]))>> 2;
00096     int acc_y = (int16_t)(((data[3] << 8) | data[4]))>> 2;
00097     int acc_z = (int16_t)(((data[5] << 8) | data[6]))>> 2;
00098 
00099     // copy the magnetometer byte data into 16 bit words
00100     int mag_x = (int16_t) (data[7] << 8) | data[8];
00101     int mag_y = (int16_t) (data[9] << 8) | data[10];
00102     int mag_z = (int16_t) (data[11] << 8) | data[12];
00103 
00104     Data values;  // struct to hold values
00105 
00106     // 0.488 mg/LSB in 4 g mode (8.1 data sheet)
00107     values.ax = 0.488e-3*acc_x;
00108     values.ay = 0.488e-3*acc_y;
00109     values.az = 0.488e-3*acc_z;
00110 
00111     // the magnetometer sensitivity is fixed at 0.1 μT/LSB
00112     values.mx = 0.1e-6*mag_x;
00113     values.my = 0.1e-6*mag_y;
00114     values.mz = 0.1e-6*mag_z;
00115 
00116     return values;
00117 }
00118 
00119 float FXOS8700CQ::get_pitch_angle(){
00120     Data values = get_values();
00121     float numerator = -1 * values.ax ;
00122     float squared_den = (values.ay * values.ay) + (values.az * values.az);
00123     float denomenator = sqrt(squared_den);
00124     float pitch_angle_radians = atan2(numerator , denomenator);
00125     float pitch_angle_degrees = pitch_angle_radians * (180 / 3.14159);
00126     return pitch_angle_degrees;
00127     }
00128 float FXOS8700CQ::get_roll_angle(){
00129     Data values = get_values();
00130     float roll_angle_radians = atan2(values.ay , values.az);
00131     float roll_angle_degrees = roll_angle_radians * (180 / 3.14159);
00132     return roll_angle_degrees;
00133     }
00134 
00135 void FXOS8700CQ::send_byte_to_reg(char byte,char reg)
00136 {
00137     char data[2];
00138     data[0] = reg;
00139     data[1] = byte;
00140     // send the register address, followed by the data
00141     int nack = i2c->write(FXOS8700CQ_ADDR,data,2);
00142     if (nack)
00143         error("No acknowledgement received!");  // if we don't receive acknowledgement, send error message
00144 
00145 }
00146 
00147 // reads a byte from a specific register
00148 char FXOS8700CQ::read_byte_from_reg(char reg)
00149 {
00150     int nack = i2c->write(FXOS8700CQ_ADDR,&reg,1,true);  // send the register address to the slave
00151     // true as need to send repeated start condition (5.10.1 datasheet)
00152     // http://www.i2c-bus.org/repeated-start-condition/
00153     if (nack)
00154         error("No acknowledgement received!");  // if we don't receive acknowledgement, send error message
00155 
00156     char rx;
00157     nack = i2c->read(FXOS8700CQ_ADDR,&rx,1);  // read a byte from the register and store in buffer
00158     if (nack)
00159         error("No acknowledgement received!");  // if we don't receive acknowledgement, send error message
00160 
00161     return rx;
00162 }
00163 
00164 // reads a series of bytes, starting from a specific register
00165 void FXOS8700CQ::read_bytes_from_reg(char reg,int number_of_bytes,char bytes[])
00166 {
00167     int nack = i2c->write(FXOS8700CQ_ADDR,&reg,1,true);  // send the slave write address and the configuration register address
00168     // true as need to send repeated start condition (5.10.1 datasheet)
00169     // http://www.i2c-bus.org/repeated-start-condition/
00170 
00171     if (nack)
00172         error("No acknowledgement received!");  // if we don't receive acknowledgement, send error message
00173 
00174     nack = i2c->read(FXOS8700CQ_ADDR,bytes,number_of_bytes);  // read bytes
00175     if (nack)
00176         error("No acknowledgement received!");  // if we don't receive acknowledgement, send error message
00177 
00178 }