FFT analysis for ADXL345

Hello All,

I want to use ADXL345 to measure spindle vibration. so far I interfaced Arduino & ADXL345 with I2C communication. I loaded available adafruit code to the arduino and tested the sensor. It seems to be working fine.

This is the code:

#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_ADXL345_U.h>

/* Assign a unique ID to this sensor at the same time */
Adafruit_ADXL345_Unified accel = Adafruit_ADXL345_Unified(12345);

void displaySensorDetails(void)
{
sensor_t sensor;
accel.getSensor(&sensor);
Serial.println("------------------------------------");
Serial.print ("Sensor: "); Serial.println(sensor.name);
Serial.print (“Driver Ver: “); Serial.println(sensor.version);
Serial.print (“Unique ID: “); Serial.println(sensor.sensor_id);
Serial.print (“Max Value: “); Serial.print(sensor.max_value); Serial.println(” m/s^2”);
Serial.print (“Min Value: “); Serial.print(sensor.min_value); Serial.println(” m/s^2”);
Serial.print (“Resolution: “); Serial.print(sensor.resolution); Serial.println(” m/s^2”);
Serial.println(”------------------------------------”);
Serial.println(””);
delay(500);
}

void displayDataRate(void)
{
Serial.print ("Data Rate: ");

switch(accel.getDataRate())
{
case ADXL345_DATARATE_3200_HZ:
Serial.print ("3200 ");
break;
case ADXL345_DATARATE_1600_HZ:
Serial.print ("1600 ");
break;
case ADXL345_DATARATE_800_HZ:
Serial.print ("800 ");
break;
case ADXL345_DATARATE_400_HZ:
Serial.print ("400 ");
break;
case ADXL345_DATARATE_200_HZ:
Serial.print ("200 ");
break;
case ADXL345_DATARATE_100_HZ:
Serial.print ("100 ");
break;
case ADXL345_DATARATE_50_HZ:
Serial.print ("50 ");
break;
case ADXL345_DATARATE_25_HZ:
Serial.print ("25 ");
break;
case ADXL345_DATARATE_12_5_HZ:
Serial.print ("12.5 ");
break;
case ADXL345_DATARATE_6_25HZ:
Serial.print ("6.25 ");
break;
case ADXL345_DATARATE_3_13_HZ:
Serial.print ("3.13 ");
break;
case ADXL345_DATARATE_1_56_HZ:
Serial.print ("1.56 ");
break;
case ADXL345_DATARATE_0_78_HZ:
Serial.print ("0.78 ");
break;
case ADXL345_DATARATE_0_39_HZ:
Serial.print ("0.39 ");
break;
case ADXL345_DATARATE_0_20_HZ:
Serial.print ("0.20 ");
break;
case ADXL345_DATARATE_0_10_HZ:
Serial.print (“0.10 “);
break;
default:
Serial.print (”??? “);
break;
}
Serial.println(” Hz”);
}

void displayRange(void)
{
Serial.print ("Range: +/- ");

switch(accel.getRange())
{
case ADXL345_RANGE_16_G:
Serial.print ("16 ");
break;
case ADXL345_RANGE_8_G:
Serial.print ("8 ");
break;
case ADXL345_RANGE_4_G:
Serial.print ("4 ");
break;
case ADXL345_RANGE_2_G:
Serial.print (“2 “);
break;
default:
Serial.print (”?? “);
break;
}
Serial.println(” g”);
}

void setup(void)
{
#ifndef ESP8266
while (!Serial); // for Leonardo/Micro/Zero
#endif
Serial.begin(9600);
Serial.println(“Accelerometer Test”); Serial.println("");

/* Initialise the sensor /
if(!accel.begin())
{
/
There was a problem detecting the ADXL345 … check your connections */
Serial.println(“Ooops, no ADXL345 detected … Check your wiring!”);
while(1);
}

/* Set the range to whatever is appropriate for your project */
accel.setRange(ADXL345_RANGE_16_G);
// accel.setRange(ADXL345_RANGE_8_G);
// accel.setRange(ADXL345_RANGE_4_G);
// accel.setRange(ADXL345_RANGE_2_G);

/* Display some basic information on this sensor */
displaySensorDetails();

/* Display additional settings (outside the scope of sensor_t) */
displayDataRate();
displayRange();
Serial.println("");
}

void loop(void)
{
/* Get a new sensor event */
sensors_event_t event;
accel.getEvent(&event);

/* Display the results (acceleration is measured in m/s^2) */
Serial.print("X: “); Serial.print(event.acceleration.x); Serial.print(” ");
Serial.print("Y: “); Serial.print(event.acceleration.y); Serial.print(” ");
Serial.print("Z: “); Serial.print(event.acceleration.z); Serial.print(” ");Serial.println("m/s^2 ");
delay(500);
}

As I move or vibrate the sensor, the output changes. Is there anyway to apply FFT to sensor output. I searched related to this but no luck. Pls help me out for applying FFT.

Thanks in advance. :slight_smile: :slight_smile: :slight_smile:

Please edit your post to add code tags, as described in "How to use this forum".

Hello Reva23,

#include <SPI.h>
#include <ESP8266WiFi.h>

//ADXL345
#define BW_RATE 0x2C //Data rate and power mode control
#define POWER_CTL 0x2D //Power Control Register
#define DATA_FORMAT 0x31 //Data format control
#define DATAX0 0x32 //X-Axis Data 0


//Nodemcu pin D5 GPIO 14 -----> pin SCL ADXL345
//Nodemcu pin D6 GPIO 12 -----> pin SDO ADXL345
//Nodemcu pin D7 GPIO 13 -----> pin SDA ADXL345
//Nodemcu pin D8 GPIO 15 -----> pin CS ADXL345
//Nodemcu pin 3.3 -----> pin VCC ADXL345
//Nodemcu pin GND -----> pin GND ADXL345

#define SS 15 //(IO15 -> IO5)

char values[10];
int16_t x, y, z;
float xg, yg, zg;

void setup() {
SPI.begin();
SPI.setDataMode(SPI_MODE2);
SPI.setBitOrder(MSBFIRST);
SPI.setFrequency(1000000);
//SPI.setClockDivider(SPI_CLOCK_DIV16);


Serial.begin(250000);

// SS Hight
pinMode(SS, OUTPUT);
digitalWrite(SS, HIGH);

// ADXL345
writeRegister(DATA_FORMAT, 0x03); // ±16g 10bit
writeRegister(POWER_CTL, 0x08); //
writeRegister(BW_RATE, 0x0F); //
}

void loop() {
// DATAX0
readRegister(DATAX0, 6, values);

// 2Byte
x = ((int16_t)values[1] << 8) | (int16_t)values[0];
y = ((int16_t)values[3] << 8) | (int16_t)values[2];
z = ((int16_t)values[5] << 8) | (int16_t)values[4];

// 0.03125 = (16*2)/(2^10)
xg = x * 0.03125;
yg = y * 0.03125;
zg = (z * 0.03125) - 1;



//
Serial.print(xg);
Serial.print("\t");
Serial.print(yg);
Serial.print("\t");
Serial.println(zg);
}

void writeRegister(char registerAddress, char value) {
// SPI
digitalWrite(SS, LOW);
//
SPI.transfer(registerAddress);
//
SPI.transfer(value);
// SPI
digitalWrite(SS, HIGH);
}

void readRegister(char registerAddress, int16_t numBytes, char * values) {
//
char address = 0x80 | registerAddress;
//
if (numBytes > 1)address = address | 0x40;
// SPI
digitalWrite(SS, LOW);
//
SPI.transfer(address);
//
for (int16_t i = 0; i < numBytes; i++) {
values[i] = SPI.transfer(0x00);
}
// SPI CS HIGH
digitalWrite(SS, HIGH);
}

Upload this code, you will get 3 columns of serial data in serial monitor.
Apply FFT to the required channel before pushing to serial…