Hello everyone!
I am trying to build a vibration datalogger for recording vibrations on a machine. It will be consist of 4 Arduino Uno with ADXL345 sensors and a Raspberry Pi for database.
The Raspberry Pi will read the data coming from Arduinos and it will insert them to a MySQL table. At the moment I am planning to use USB ports for communication (max distance from Raspberry Pi to Arduino will be less than 3 meters).
The required resolution is 4G and data rate is approximately 1000Hz (thus I selected 800Hz).
At the moment I am saving the readings to a file on Raspberry Pi, and my main problem is that I am getting 70-80 readings per second. I am not an coding expert and I have started with ADXL345 basic code which can be found everywhere and done little modifications.
Could anyone can help me to find the problem with data rate?
//Add the SPI library so we can communicate with the ADXL345 sensor
#include <SPI.h>
//Assign the Chip Select signal to pin 10.
int CS=10;
char POWER_CTL = 0x2D;
char DATA_FORMAT = 0x31;
char BW_RATE = 0x2C;
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
//This buffer will hold values read from the ADXL345 registers.
char values[10];
//These variables will be used to hold the x,y and z axis accelerometer values.
int x,y,z;
void 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(CS, OUTPUT);
//Before communication starts, the Chip Select pin needs to be set high.
digitalWrite(CS, HIGH);
writeRegister(DATA_FORMAT, 0x01);
writeRegister(POWER_CTL, 0x08);
writeRegister(BW_RATE, 0x0E);
//Create a serial connection to display the data on the terminal.
Serial.begin(9600);
}
void loop(){
//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.
x = ((int)values[1]<<8)|(int)values[0];
y = ((int)values[3]<<8)|(int)values[2];
z = ((int)values[5]<<8)|(int)values[4];
Serial.print(x);
Serial.print(",");
Serial.print(y);
Serial.print(",");
Serial.println(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 writeRegister(char registerAddress, char value){
//Set Chip Select pin low to signal the beginning of an SPI packet.
digitalWrite(CS, 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(CS, 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 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(CS, 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(CS, HIGH);
}
Regards