Serial communication not working when class is instantiated in Arduino Environment - c++

Question

I'm trying to write code for my Arduino Mega to communicate with ADXL345 accelerometer using c++ style library.
This is my Accelerometer.h file:
#include <Wire.h>
#define ADXL345 (0x53) // I2C Address of ADXL345 accelerometer
struct Acceleration
{
float x;
float y;
float z;
};
class Accelerometer
{
public:
Accelerometer(void); // Constructor
Acceleration readData(void); // Read sensor data
private:
char buffer[6]; // Buffer to store data (x, y, z: LSB and MSB of each)
char DATA_FORMAT; // Address of DATA_FORMAT Register
char POWER_CTL; // Address of POWER_CTL Register
char DATAX0; // Address of X-Axis LSB Data
char DATAX1; // Address of X-Axis MSB Data
char DATAY0; // Address of Y-Axis LSB Data
char DATAY1; // Address of Y-Axis MSB Data
char DATAZ0; // Address of Z-Axis LSB Data
char DATAZ1; // Address of Z-Axis MSB Data
void writeToAccelerometer(char address, char value);
void readFromAccelerometer(char address, int numOfBytes);
};
And this is my Accelerometer.cpp file:
#include "Accelerometer.h"
#include <Wire.h>
Accelerometer::Accelerometer()
{
Wire.begin(); // Initialize I2C bus
writeToAccelerometer(DATA_FORMAT, 0x01); // +/- 4g range
writeToAccelerometer(POWER_CTL, 0x08); // Measurement Mode
DATA_FORMAT = 0x31; // Address of DATA_FORMAT Register
POWER_CTL = 0x2D; // Address of POWER_CTL Register
DATAX0 = 0x32; // Address of X-Axis LSB Data
DATAX1 = 0x33; // Address of X-Axis MSB Data
DATAY0 = 0x34; // Address of Y-Axis LSB Data
DATAY1 = 0x35; // Address of Y-Axis MSB Data
DATAZ0 = 0x36; // Address of Z-Axis LSB Data
DATAZ1 = 0x37; // Address of Z-Axis MSB Data
}
void Accelerometer::writeToAccelerometer(char address, char value)
{
Wire.beginTransmission(ADXL345); // start transmission to ADXL345
Wire.write(address); // send register address
Wire.write(value); // send value to write
Wire.endTransmission(); // end transmission
}
void Accelerometer::readFromAccelerometer(char address, int numOfBytes)
{
Wire.beginTransmission(ADXL345); // start transmission to ADXL345
Wire.write(address); // send register address
Wire.endTransmission(); // end transmission
Wire.beginTransmission(ADXL345); // start transmission to ADXL345
Wire.requestFrom(ADXL345, numOfBytes); // request some bytes from device
int i = 0;
while(Wire.available()) // while there is data
{
buffer[i] = Wire.read(); // receive a byte and save it in the buffer
i++;
}
Wire.endTransmission(); // end transmission
}
Acceleration Accelerometer::readData()
{
Acceleration R;
readFromAccelerometer(DATAX0, 6); // Read data from sensor
// Merge of data and conversion to int format
int x_acceleration = (((int)buffer[1]) << 8) | buffer[0];
int y_acceleration = (((int)buffer[3]) << 8) | buffer[2];
int z_acceleration = (((int)buffer[5]) << 8) | buffer[4];
R.x = x_acceleration*0.0078;
R.y = x_acceleration*0.0078;
R.z = x_acceleration*0.0078;
return R;
}
I'm using this library im my Arduino sketch with this code:
#include <Wire.h>
#include "Accelerometer.h"
Accelerometer accel;
Acceleration Racc;
void setup()
{
Serial.begin(9600); // Start serial for outbut at 9600 bps
}
void loop()
{
Racc = accel.readData();
// Print data
Serial.print("ACCELERATION - X: ");
Serial.print( Racc.x );
Serial.print(" G / Y: ");
Serial.print( Racc.y );
Serial.print(" G / Z: ");
Serial.print( Racc.z );
Serial.print(" G\n");
delay(100);
}
This code is compilated without erros. However, because of the instantiation of Accelerometer class, Serial communication is not working (I can't see any text in Serial Monitor). When I remove the class instance of the code (letting just Serial communication in code), I can see what is print in Serial Monitor.
Does anybody have any idea about what is going on? I would appreciate any help.

Answer 1

As the ADXL345 can operate either SPI or I2C it needs to be configured, as such. In your case of trying to use it as I2C, the CS of the ADXL345 need to be tied to 3.3V
I2C mode is enabled if the CS pinis tied high to VDD I/O. The CS pin
should always be tied high to VDD I/O or be driven by an external
controller because there is nodefault mode if the CS pin is left
unconnected. Therefore, not taking these precautions may result in an
inability to ommunicatewith the part.
Where in your above code I do not see any pins configured as output to drive the CS.
It has been my experience that when the I2C (wire.h) library is not properly connected to a device it can be blocking. Which is similar to your described symptom here.
You may want to reference your code against others, such as https://github.com/jenschr/Arduino-libraries/tree/master/ADXL345. which appears to fully support the many features of the ADXL345 over I2C