[solved] Adxl345 incorrect readings ;(

Hello I bought 3 accelerometers and it seems that none of which is working properly, in particular positions, as on the picture when the acceleration should be as below picture, readings numbers are different, and aren’t even close to correct value ( I didn’t put any values for the offset registers so lets say only difference in values between positions is the issue).

My question is are those accelerometers definetly corrupted or is it some other issue that could be solved somehow, I include data sheet for adxl345 accelerometer and order of position I made measurements and code which is mostly copied from sparkfun basic example.

Those are measurements with 10 bits resolution:

position1// 8 :-24,-11,-123 9 :-105,-117,31 10 :-2,-19,91
position2// 8 :-24,-13,63 9 :-103,-118,-21 10 :-5,-18,18
position3// 8 :-25,28,98 9 :-103,-88,7 10 :-5,16,61
position4// 8 :-26,-49,97 9 :-104,-148,5 10 :-2,-50,53
position5// 8 :15,-14,99 9 :-72,-118,7 10 :31,-17,54
position6// 8 :-64,-10,97 9 :-134,-117,3 10 :-37,-17,58

Those are measurements with 13 bits resolution:

position1// 8 :-182,-47,-43 9 :-56,-975,-166 10 :-27,-67,-95
position2// 8 :-198,-130,1067 9 :-72,-706,81 10 :-1,-392,-67
position3// 8 :-171,-23,791 9 :-66,-704,51 10 :0,-127,-9
position4// 8 :-172,-389,-13 9 :-80,-1188,53 10 :-7,-397,-84
position5// 8 :-511,-60,-26 9 :-52,-928,32 10 :-9,-138,-70
position6// 8 :-126,-74,787 9 :-62,-928,66 10 :-39,-159,-25

//Add the SPI library so we can communicate with the ADXL345 sensor
#include <SPI.h>
#include <LiquidCrystal.h>


LiquidCrystal lcd(2, 3, 4, 5, 6, 7);

//Assign the Chip Select signal to pin 10.


//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


char OFSX = 0x1E; //Z-Axis offset
char OFSY = 0x1F; //Z-Axis offset
char OFSZ = 0x20; //Z-Axis offset


//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.
float x,y,z;
int x1,y1,z1;
int j,k;
int CS=8;

int analogPin = 1;
int button=0;


void setup(){ 
  //Initiate an SPI communication instance.
  SPI.begin();
  //Configure the SPI connection for the ADXL345.
  SPI.setDataMode(SPI_MODE3);

  //Create a serial connection to display the data on the terminal.
  Serial.begin(9600);
  
  //Set up the Chip Select pin to be an output from the Arduino.
  pinMode(8, OUTPUT);       //cs
  pinMode(9, OUTPUT);
  pinMode(10, OUTPUT);      //cs
  //Before communication starts, the Chip Select pin needs to be set high.
  digitalWrite(8, HIGH);
  digitalWrite(9, HIGH);
  digitalWrite(10, HIGH);


  writeRegister(OFSX,0x00);//zerowanie offsetów
  writeRegister(OFSY,0x00);//zerowanie offsetów
  writeRegister(OFSZ,0x00);//zerowanie offsetów

  
  //Put the ADXL345 into +/- 2G range by writing the value 0x00 to the DATA_FORMAT register.
  writeRegister(DATA_FORMAT,0x01| 0x02| 0x08);
  //Put the ADXL345 into Measurement Mode by writing 0x08 to the POWER_CTL register.
  writeRegister(POWER_CTL, 0x08);  //Measurement mode  
  lcd.begin(16, 2);
  // Print a message to the LCD.
 
  lcd.display();
}

void loop(){
  
    if(button = analogRead(analogPin)>500){
  //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.
  for(j=0;j<3;j++){


  Serial.print(CS+j);
  Serial.print(" :");
  
  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].
  x1 = ((int)values[1]<<8)|(int)values[0];
  //The Y value is stored in values[2] and values[3].
  y1 = ((int)values[3]<<8)|(int)values[2];
  //The Z value is stored in values[4] and values[5].
  z1 = ((int)values[5]<<8)|(int)values[4];

  x=x1/1.0f;
  y=y1/1.0f;
  z=z1/1.0f;
  
  
  //Print the results to the terminal.
  Serial.print(x, 5);
  Serial.print(',');
  Serial.print(y, 5);
  Serial.print(',');
  Serial.println(z, 5);      
  delay(10); 
  
  lcd.clear();
  lcd.print("x=");
  lcd.print(x, 2);
  lcd.print(", ");
  lcd.print("y=");
  lcd.print(y, 2);
  lcd.print(',');
  
  lcd.setCursor(2, 1);
  lcd.print("z=");  
  lcd.print(z, 2);      
  lcd.print(" (g)");
  lcd.setCursor(0, 1);
    

  delay(500);
  lcd.clear();
  }

  j=0;
  CS=8;
  }


}


//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){
  
  
  for(k=0;k<3;k++){
  //Set Chip Select pin low to signal the beginning of an SPI packet.
  digitalWrite(CS+k, 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+k, HIGH);
  }
  j=0;
  delay(10);
  
}





//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+j, 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+j, HIGH);
  delay(10);

 }

ADXL345.pdf (482 KB)

What are the 8,9,10 ? and what are the three numbers behind the 8,9,10 ?

Did you try a library ?
For example the Adafruit library in SPI mode : GitHub - adafruit/Adafruit_ADXL345: Unified driver for the ADXL345 Accelerometer

Is the sensor in SPI mode ? How do you know ?

8,9,10 are cs pins for each accelerometer (for example 8 means data from accelerometer connected with pin 8 ).

I didn't try adafruit library, did you? Is there example code how to use it?

It suppose to be in 4 wire SPI mode, if SPI bit in DATA_FORMAT register is set to 0 according to data sheet:

Start with just one sensor.

Looking at the numbers, I think I can see the changing of the x,y,z values. But not all three sensors are in the same position, or the numbers are wrong.

Do you have a module with the ADXL345 ? Is the module compatible with 5V signals ?
Which Arduino board do you use ? I hope you don't use a 5V Arduino board with this 3.3V sensor.

The Adafruit library comes with an example. If the library is loaded into the Arduino IDE, the example(s) are added to the menu.
The ADXL345 unified library is in the Library Manager. You have to install the "Adafruit Unified Sensor" as well.

I use the Arduino pro micro with 3,3V.

The readings are from the same position more or less of each accelerometer.

I tried and added this adafruit library but the only example called "sensortest" works only with I2C and I can only use SPI for my project.

I tried and added this adafruit library but the only example called "sensortest" works only with I2C and I can only use SPI for my project.

But you could use this library, and I2C to test the sensor and verify proper operation.

It is very unlikely that 3 sensors would be bad, so something else is wrong.

What sort of nonsense is this comment?

  //Put the ADXL345 into +/- 2G range by writing the value 0x00 to the DATA_FORMAT register.
  writeRegister(DATA_FORMAT,0x01| 0x02| 0x08);

The spi is in the source code, perhaps that is not fully tested yet or the object needs to be created with the parameters for spi.

Okay yes sorry for the comment this is pretty raw program yet and I didn’t change the comments when I changed values in this case the range is up to 16g.

I got code from here:https://github.com/jenschr/Arduino-libraries/blob/master/ADXL345/examples/ADXL345_no_library/BareBones_ADXL345.pde

#include <Wire.h>

#define DEVICE (0x53) // Device address as specified in data sheet 

byte _buff[6];

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


int analogPin = 1;
int button=0;

void setup()
{
  Wire.begin();        // join i2c bus (address optional for master)
  Serial.begin(57000);  // start serial for output. Make sure you set your Serial Monitor to the same!
  Serial.print("init");
  
  //Put the ADXL345 into +/- 4G range by writing the value 0x01 to the DATA_FORMAT register.
  writeTo(DATA_FORMAT, 0x01| 0x02| 0x08);
  //Put the ADXL345 into Measurement Mode by writing 0x08 to the POWER_CTL register.
  writeTo(POWER_CTL, 0x08);
}

void loop()
{
  if(button = analogRead(analogPin)>500){
  for(int i=0;i<2;i++){
  readAccel(); // read the x/y/z tilt
  delay(500); // only read every 0,5 seconds
  }
  }
}

void readAccel() {
  uint8_t howManyBytesToRead = 6;
  readFrom( DATAX0, howManyBytesToRead, _buff); //read the acceleration data from the ADXL345

  // each axis reading comes in 10 bit resolution, ie 2 bytes.  Least Significat Byte first!!
  // thus we are converting both bytes in to one int
  int x = (((int)_buff[1]) << 8) | _buff[0];   
  int y = (((int)_buff[3]) << 8) | _buff[2];
  int z = (((int)_buff[5]) << 8) | _buff[4];
  Serial.print("x: ");
  Serial.print( x );
  Serial.print(" y: ");
  Serial.print( y );
  Serial.print(" z: ");
  Serial.println( z );
}

void writeTo(byte address, byte val) {
  Wire.beginTransmission(DEVICE); // start transmission to device 
  Wire.write(address);             // send register address
  Wire.write(val);                 // send value to write
  Wire.endTransmission();         // end transmission
}

// Reads num bytes starting from address register on device in to _buff array
void readFrom(byte address, int num, byte _buff[]) {
  Wire.beginTransmission(DEVICE); // start transmission to device 
  Wire.write(address);             // sends address to read from
  Wire.endTransmission();         // end transmission

  Wire.beginTransmission(DEVICE); // start transmission to device
  Wire.requestFrom(DEVICE, num);    // request 6 bytes from device

  int i = 0;
  while(Wire.available())         // device may send less than requested (abnormal)
  { 
    _buff[i] = Wire.read();    // receive a byte
    i++;
  }
  Wire.endTransmission();         // end transmission
}

Okay I’ve tested it with I2C with the following code, and results are for accelerometer connected with cs8 in previous measurements:

pos 1
x: -190 y: -89 z: 507
pos 2
x: -193 y: -72 z: 1065

pos3
x: -186 y: 230 z: 772

pos4
x: -197 y: -391 z: 776

pos5
x: 134 y: -66 z: 781

pos6
x: -510 y: -89 z: 787

so despite the no offset, the difference in each axis between two extreme positions are around 600 so it seems it works kind of properly since data sheet says 4mg/LSB so difference is around 2 g:

the question then is why it does not work like thatwith SPI yet…

It doesn't make sense to work with 16g range until you fully understand the operation at the lowest g range. That way you know that +/- 1 g will make a large and known difference in the readings.

yes I understand that, but I used it before with +-2g which is the smallest range and one of the sensors didn't give any value in some axis as I remember it was x and y in one sensor and z in the other one I read somewhere that good idea is to change the range and try again.

So I did that for that and at least values are changing right now but unfortunately not how it suppose to...

If you bought the accelerometers from a cheap Chinese eBay seller, the chances are rather high that they are reject or counterfeit parts.

On the other hand, if your program is wrong, none of them will function correctly, either.

The use of the Wire library is wrong. Both in your sketch and in that link.

The Wire.requestFrom() should not be encapsulated by Wire.beginTransmission() and Wire.endTransmission. The Wire.available() could be checked for every byte, but also just once, or the return value of Wire.requestFrom() can be used.

I prefer something like this:

// Reads num bytes starting from address register on device in to _buff array
void readFrom(byte address, int num, byte _buff[]) {
  Wire.beginTransmission(DEVICE); // start transmission to device
  Wire.write(address);             // sends address to read from
  Wire.endTransmission();         // end transmission

  int n = Wire.requestFrom(DEVICE, num);    // request 6 bytes from device
  if( n==num) {
    Wire.readBytes( _buff, n);
  }
}

That does not solve your problem, since the I2C is working.
Can you get the same values with SPI as with I2C ?

:slight_smile:

thanks for the help I figured it out finally ( meaning I found solution in some comment under the sparkfun tutorial) it wasn’t any problem with SPI just with declaring the values buffer as char which caused the second byte of value to have wrong number because of sign bit so the solution was just to change values array to byte also in read register function.

I post the corrected code for my problem in case somebody else have that problem adding that it’s still very raw version:

//Add the SPI library so we can communicate with the ADXL345 sensor
#include <SPI.h>
#include <LiquidCrystal.h>


LiquidCrystal lcd(2, 3, 4, 5, 6, 7);

//Assign the Chip Select signal to pin 10.


//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


char OFSX = 0x1E; //Z-Axis offset
char OFSY = 0x1F; //Z-Axis offset
char OFSZ = 0x20; //Z-Axis offset


//This buffer will hold values read from the ADXL345 registers.
byte values[10];
//These variables will be used to hold the x,y and z axis accelerometer values.
float x,y,z;
int x1,y1,z1;
int j,k;
int CS=8;

int analogPin = 1;
int button=0;


void setup(){ 
  //Initiate an SPI communication instance.
  SPI.begin();
  //Configure the SPI connection for the ADXL345.
  SPI.setDataMode(SPI_MODE3);

  //Create a serial connection to display the data on the terminal.
  Serial.begin(9600);
  
  //Set up the Chip Select pin to be an output from the Arduino.
  pinMode(8, OUTPUT);       //cs
  pinMode(9, OUTPUT);
  pinMode(10, OUTPUT);      //cs
  //Before communication starts, the Chip Select pin needs to be set high.
  digitalWrite(8, HIGH);
  digitalWrite(9, HIGH);
  digitalWrite(10, HIGH);


  writeRegister(OFSX,0x00);//zerowanie offsetów
  writeRegister(OFSY,0x00);//zerowanie offsetów
  writeRegister(OFSZ,0x00);//zerowanie offsetów

  
  //Put the ADXL345 into +/- 2G range by writing the value 0x00 to the DATA_FORMAT register.
  writeRegister(DATA_FORMAT,0x01| 0x02| 0x08);
  //Put the ADXL345 into Measurement Mode by writing 0x08 to the POWER_CTL register.
  writeRegister(POWER_CTL, 0x08);  //Measurement mode  
  lcd.begin(16, 2);
  // Print a message to the LCD.
 
  lcd.display();
}

void loop(){
  
    if(button = analogRead(analogPin)>500){
  //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.
  for(j=0;j<3;j++){


  Serial.print(CS+j);
  Serial.print(" :");
  
  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].
  x1 = ((int)values[1]<<8)| values[0];
  //The Y value is stored in values[2] and values[3].
  y1 = ((int)values[3]<<8)| values[2];
  //The Z value is stored in values[4] and values[5].
  z1 = ((int)values[5]<<8)| values[4];

  x=x1/1.0f;
  y=y1/1.0f;
  z=z1/1.0f;
  
  
  //Print the results to the terminal.
  Serial.print(x, 5);
  Serial.print(',');
  Serial.print(y, 5);
  Serial.print(',');
  Serial.println(z, 5);      
  delay(10); 
  
  lcd.clear();
  lcd.print("x=");
  lcd.print(x, 2);
  lcd.print(", ");
  lcd.print("y=");
  lcd.print(y, 2);
  lcd.print(',');
  
  lcd.setCursor(2, 1);
  lcd.print("z=");  
  lcd.print(z, 2);      
  lcd.print(" (g)");
  lcd.setCursor(0, 1);
    

  delay(500);
  lcd.clear();
  }

  j=0;
  CS=8;
  }


}


//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){
  
  
  for(k=0;k<3;k++){
  //Set Chip Select pin low to signal the beginning of an SPI packet.
  digitalWrite(CS+k, 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+k, HIGH);
  }
  j=0;
  delay(10);
  
}





//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(byte registerAddress, byte numBytes, byte 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+j, 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+j, HIGH);
  delay(10);

 }