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Accelerometer.cpp
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Accelerometer.cpp
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#include "Arduino.h"
#include "Accelerometer.h"
//This is a list of some of the registers available on the ADXL345.
//To learn more about these and the rest of the registers on the ADXL345, read the datasheet!
char POWER_CTL = 0x2D; //Power Control Register
char DATA_FORMAT = 0x31;
char DATAX0 = 0x32; //X-Axis Data 0
char DATAX1 = 0x33; //X-Axis Data 1
char DATAY0 = 0x34; //Y-Axis Data 0
char DATAY1 = 0x35; //Y-Axis Data 1
char DATAZ0 = 0x36; //Z-Axis Data 0
char DATAZ1 = 0x37; //Z-Axis Data 1
Accelerometer::Accelerometer(int chipSelect) {
mChipSelect = chipSelect;
setup();
}
Accelerometer::Accelerometer(int chipSelect, float threshold){
mChipSelect = chipSelect;
mThreshold = threshold;
setup();
}
Accelerometer::Accelerometer(int chipSelect, float threshold, int eventThreshold){
mChipSelect = chipSelect;
mThreshold = threshold;
mEventThreshold = eventThreshold;
setup();
}
void Accelerometer::setThreshold(int threshold) {
mThreshold = threshold;
Serial.print("threshold: ");
Serial.println(mThreshold);
}
void Accelerometer::setEventThreshold(int eventThreshold) {
mEventThreshold = eventThreshold;
Serial.print("event threshold: ");
Serial.println(mEventThreshold);
}
void Accelerometer::setup() {
//Initiate an SPI communication instance.
SPI.begin();
//Configure the SPI connection for the ADXL345.
SPI.setDataMode(SPI_MODE3);
//Set up the Chip Select pin to be an output from the Arduino.
pinMode(mChipSelect, OUTPUT);
//Before communication starts, the Chip Select pin needs to be set high.
digitalWrite(mChipSelect, HIGH);
//Put the ADXL345 into +/- 4G range by writing the value 0x01 to the DATA_FORMAT register.
writeRegister(DATA_FORMAT, 0x01);
//For +/- 4G (8G range) with 10 bits, scale is calculated as 8/2^10
scale = 0.0078125;
//Put the ADXL345 into Measurement Mode by writing 0x08 to the POWER_CTL register.
writeRegister(POWER_CTL, 0x08); //Measurement mode
Serial.println("Accelerometer initialised. Configuration");
Serial.print("chipSelect: ");
Serial.println(mChipSelect);
Serial.print("threshold: ");
Serial.println(mThreshold);
Serial.print("event threshold: ");
Serial.println(mEventThreshold);
}
String Accelerometer::processor() {
String output;
for (int axis=0; axis<3; axis++) {
average_delta_a[axis] = 0;
}
for (int i=0; i<iterations; i++) {
readAccelerometer();
for (int axis=0; axis<3; axis++) {
//delta_a[axis][i]=current_acceleration[axis] - previous_acceleration[axis];
//average_delta_a[axis] += delta_a[axis][i];
average_delta_a[axis] += current_acceleration[axis] - previous_acceleration[axis];
}
delay(delta);
}
for (int axis=0; axis<3; axis++) {
average_delta_a[axis] = average_delta_a[axis] / iterations;
if (abs(average_delta_a[axis]) > mThreshold
&& (millis() - previous_event_time[axis]) > mEventThreshold) {
if (previous_event[axis] > 0 && average_delta_a[axis] < 0) { // turning point
output = axes[axis][0];
} else if (previous_event[axis] < 0 && average_delta_a[axis] > 0) { // turning point
output = axes[axis][1];
}
previous_event_time[axis] = millis(); // update last event
previous_event[axis] = average_delta_a[axis]; // store this last acceleration value
}
}
// store previous acceleration
for (int i=0; i<NELEMS(current_acceleration); i++) {
previous_acceleration[i] = current_acceleration[i];
}
return output;
}
void Accelerometer::readAccelerometer() {
//Reading 6 bytes of data starting at register DATAX0 will retrieve the x,y and z acceleration values from the ADXL345.
//The results of the read operation will get stored to the values[] buffer.
readRegister(DATAX0, 6, values);
//The ADXL345 gives 10-bit acceleration values, but they are stored as bytes (8-bits). To get the full value, two bytes must be combined for each axis.
//The X value is stored in values[0] and values[1].
x = ((int)values[1]<<8)|(int)values[0];
current_acceleration[0] = scale*x;
//The Y value is stored in values[2] and values[3].
y = ((int)values[3]<<8)|(int)values[2];
current_acceleration[1] = scale*y;
//The Z value is stored in values[4] and values[5].
z = ((int)values[5]<<8)|(int)values[4];
current_acceleration[2] = scale*z;
}
//This function will write a value to a register on the ADXL345.
//Parameters:
// char registerAddress - The register to write a value to
// char value - The value to be written to the specified register.
void Accelerometer::writeRegister(char registerAddress, char value){
//Set Chip Select pin low to signal the beginning of an SPI packet.
digitalWrite(mChipSelect, LOW);
//Transfer the register address over SPI.
SPI.transfer(registerAddress);
//Transfer the desired register value over SPI.
SPI.transfer(value);
//Set the Chip Select pin high to signal the end of an SPI packet.
digitalWrite(mChipSelect, HIGH);
}
//This function will read a certain number of registers starting from a specified address and store their values in a buffer.
//Parameters:
// char registerAddress - The register addresse to start the read sequence from.
// int numBytes - The number of registers that should be read.
// char * values - A pointer to a buffer where the results of the operation should be stored.
void Accelerometer::readRegister(char registerAddress, int numBytes, char * values){
//Since we're performing a read operation, the most significant bit of the register address should be set.
char address = 0x80 | registerAddress;
//If we're doing a multi-byte read, bit 6 needs to be set as well.
if(numBytes > 1)address = address | 0x40;
//Set the Chip select pin low to start an SPI packet.
digitalWrite(mChipSelect, LOW);
//Transfer the starting register address that needs to be read.
SPI.transfer(address);
//Continue to read registers until we've read the number specified, storing the results to the input buffer.
for(int i=0; i<numBytes; i++){
values[i] = SPI.transfer(0x00);
}
//Set the Chips Select pin high to end the SPI packet.
digitalWrite(mChipSelect, HIGH);
}