2010 Accelerometer I2C Object/Class

Hey so we discovered that the 2010 Accelerometer is not Analog it is Completely Digital.

And the Class the Java API provides is for the 2009 Analog Accelerometer.

It even says in the Documentation that they forgot to write a class for the new accelerometer and will try to add it soon.

But Soon isn’t soon enough. (Patience Fail)

Does anyone know how to go about extending the I2C class in order to create a valid Accelerometer Class?

This would be unbelievable helpful.

I am working on one now. I have a class for an I2C compass which is now working great. Accelerometer is next.

It should be trivial to port the C++ version that I posted. C/C++ I2C implementation on the cRio - NI Community


We converted the code to Java and are going to test it tomorrow.

One thing that we had to change was that instead of using enumerations we used arrays.

This was because the Version of Java the robot is running on does not support the use of enumerations, but i don’t see how that could affect the return values.

Again Thanks A Lot!!:slight_smile:

I am saddened our ported code did not work.

It may be that we just didnt translate some of the syntax correctly or something else IDK.
Returned 0.0

Heres the code

package edu.wpi.first.wpilibj.templates;
import edu.wpi.first.wpilibj.*;


  • @author ported to Java by Sam Meyer

  • ADXL345 Accelerometer on I2C.

  • This class alows access to a Analog Devices ADXL345 3-axis accelerometer on an I2C bus.

  • This class assumes the default (not alternate) sensor address of 0x3A (8-bit address).
    public class ADXL345 extends SensorBase
    private static final int kAddress = 0x3A;
    private static final int kPowerCtlRegister = 0x2D;
    private static final int kDataFormatRegister = 0x31;
    private static final int kDataRegister = 0x32;
    private static final double kGsPerLSB = 0.004;

      * PowerCtlFields
      * *********************************************/
     private static final int kPowerCtl_Link = 0x20;
     private static final int kPowerCtl_AutoSleep = 0x10;
     private static final int kPowerCtl_Measure = 0x08;
     private static final int kPowerCtl_Sleep = 0x04;
      * PowerCtlFields
      * *********************************************/
     private static final int kDataFormat_SelfTest = 0x80;
     private static final int kDataFormat_SPI = 0x40;
     private static final int kDataFormat_IntInvert = 0x20;
     private static final int kDataFormat_FullRes = 0x08;
     private static final int kDataFormat_Justify = 0x04;
      * DataFormat_Range
      * *********************************************/
     private static final int kRange_2G = 0x00;
     private static final int kRange_4G = 0x01;
     private static final int kRange_8G = 0x02;
     private static final int kRange_16G = 0x03;
      * Axes
      * *********************************************/
     private static final int kAxis_X = 0x00;
     private static final int kAxis_Y = 0x02;
     private static final int kAxis_Z = 0x04;
      * The Default Constructor
      * @param slot The slot of the digital module that the sensor is plugged into.
      * The default range is 2G (0x00)
     public ADXL345(int slot)
         this(slot, 0x00);    // kRange_2G (0x00) is default
      * Constructor.
      * @param slot The slot of the digital module that the sensor is plugged into.
      * @param range The range (+ or -) that the accelerometer will measure.
     public ADXL345(int slot, int range)
         m_i2c = null;
         DigitalModule module = DigitalModule.getInstance(slot);
         m_i2c = module.getI2C(kAddress);
         m_i2c.write(kPowerCtlRegister, kPowerCtl_Measure);
         m_i2c.write(kDataFormatRegister, kDataFormat_FullRes | (int)range);
     public static final int] Axes = {0x00, 0x02, 0x04};
     private I2C m_i2c;
      * @param Axis IMPORTANT Axes must be an integer: X = 0x00, Y = 0x02, Z = 0x04
      * @return the acceleration in Gs
     public double getAcceleration(int Axis)
         byte] rawAccel = new byte[2];
         m_i2c.read(kDataRegister + (int)Axis, 2, rawAccel);
         // Sensor is little endian... swap bytes
         byte temp = rawAccel[0];
         rawAccel[0] = rawAccel[1];
         rawAccel[1] = temp;
         int partialAccel = rawAccel[0] * 0x100 + rawAccel[1];
         return partialAccel * kGsPerLSB;


Please if you see any mistakes post them.

Also if we cant get this to work where do you buy the analog accelerometer from last year?

We also attempted a I2C accelerometer port and read 0.0 on x,y, and z.

I think the next step we may take is to flash our crio for C programming and see if we read anything but 0 in that environment.

Does anyone know if they plan to release a new update for Java with support for an I2C Accelerometer anytime soon.

In the documentation it said that they would release it in later update.

Also in case this never works is it legal to use the analog accelerometer from last year and just use the Accelerometer class in Java that was built for the analog Accelerometer?

I’m not sure if it has been ported to Java or not… I’ll check on that.

Yes, it is legal to use the Accelerometers from last year.

does anyone know where to buy the Analog Accelerometer Breakout ?

You can’t get the exact board from last year since it was made custom for FIRST… Here is a reasonable replacement: http://www.sparkfun.com/commerce/product_info.php?products_id=849

Alternately, you could manufacture your own from the designs posted of last year’s boards.


Here is java class for the ADXL345 when connected as I2C device at default address.

/* Copyright (c) FIRST 2008. All Rights Reserved.                             */
/* Open Source Software - may be modified and shared by FRC teams. The code   */
/* must be accompanied by the FIRST BSD license file in the root directory of */
/* the project.                                                               */

package edu.wpi.first.wpilibj;

 * digital accelerometer from the 2010 KOP
 * this implementation just gets the 3 axis values and allows setting the range
 * Possible enhancements:
 *      Add access to other features of the chip
 *      Add measurement of error during intialization and set channel offsets
public class ADXL345DigitalAccelerometer extends SensorBase {
    private I2C i2c;
    // default address
    private static final byte kAddress = 0x3A;
    // register map from datasheet
    private static final byte OFSX = 0x1E;
    private static final byte OFSY = 0x1F;
    private static final byte OFSZ = 0x20;
    private static final byte BW_RATE = 0x2C;
    private static final byte  POWER_CTL = 0x2D;
    private static final byte DATA_FORMAT = 0x31;
    private static final byte DATAX0 = 0x32;
    private static final byte DATAY0 = 0x34;
    private static final byte DATAZ0 = 0x36;
    private static final byte FIFO_CTL = 0x38;
    private static final byte FIFO_STATUS = 0x39;

    // would use enums here if we had them
    // BW_RATE 0x2C
    private static final byte BW_RATE_R3200B1600 = 0x0F;
    private static final byte BW_RATE_R1600B0800 = 0x0E;
    private static final byte BW_RATE_R0800B0400 = 0x0D;
    private static final byte BW_RATE_R0400B0200 = 0x0C;
    private static final byte BW_RATE_R0200B0100 = 0x0B;
    private static final byte BW_RATE_R0100B0050 = 0x0A;
    private static final byte BW_RATE_R0050B0025 = 0x09;
    private static final byte BW_RATE_R0025B0012 = 0x08;
    private static final byte BW_RATE_R0012B0006 = 0x07;
    private static final byte BW_RATE_R0006B0003 = 0x06;

    private static final byte BW_RATE_LOW_POWER = 0x10;
    // POWER_CTL 0x2D
    private static final byte POWER_CTL_LINK = 0x20;
    private static final byte POWER_CTL_AUTO_SLEEP = 0x10;
    private static final byte POWER_CTL_MEASURE = 0x08;
    private static final byte POWER_CTL_SLEEP = 0x04;
    private static final byte POWER_CTL_WAKEUP8 = 0x00;
    private static final byte POWER_CTL_WAKEUP4 = 0x01;
    private static final byte POWER_CTL_WAKEUP2 = 0x02;
    private static final byte POWER_CTL_WAKEUP1 = 0x03;

    public static final byte DATA_FORMAT_02G = 0x00;
    public static final byte DATA_FORMAT_04G = 0x01;
    public static final byte DATA_FORMAT_08G = 0x02;
    public static final byte DATA_FORMAT_16G = 0x03;

    // store the current
    private byte range = DATA_FORMAT_02G;

    public class ADXL345Exception extends RuntimeException {

         * Create a new exception with the given message
         * @param message the message to pass with the exception
        public ADXL345Exception(String message) {


    // constuctior with slot number parameter
    public ADXL345DigitalAccelerometer(int slot) {
        i2c = new I2C( DigitalModule.getInstance(slot), kAddress );

    // initialize the sensor
    public void intitialize()
        // set BW_RATE
        i2c.write(BW_RATE, BW_RATE_R0100B0050);
        // set POWER_CTL
        i2c.write(POWER_CTL, POWER_CTL_MEASURE);

    // set the range (default is =/- 2g
    public void setRange( byte rangeParam )
        if ( !( rangeParam == DATA_FORMAT_02G ||
                rangeParam == DATA_FORMAT_04G ||
                rangeParam == DATA_FORMAT_08G ||
                rangeParam == DATA_FORMAT_16G ) )
            throw new ADXL345Exception("Invalid range!");

        range = rangeParam;

        i2c.write(DATA_FORMAT, range);

    // get acceleration routines
    public double getXAxis()
        return getAxis( DATAX0 );

    public double getYAxis()
        return getAxis( DATAY0 );

    public double getZAxis()
        return getAxis( DATAZ0 );

    protected double getAxis( byte registerParam )
        // setup array for our data
        byte] data = new byte[2];
        // read consecutive registers
        this.i2c.read( registerParam, (byte) data.length, data);

        // convert to 2s complement integer
        // [0] has low byte [1] has the high byte
        // jave does not have unsigned so we have to do it this way
        int intResult = ( data[0] & 0xFF ) | ( data[1] << 8 );

        // convert to double based on 10 bit result
        double returnValue = (double)intResult / 512.0 ;

        // now scale based upon our range
        switch( range )
            case DATA_FORMAT_02G:
                returnValue *= 2.0;
            case DATA_FORMAT_04G:
                returnValue *= 4.0;
            case DATA_FORMAT_08G:
                returnValue *= 8.0;
            case DATA_FORMAT_16G:
                returnValue *= 16.0;
        return returnValue;

Note, the sparkfun board is 3.3V not 5.0V so you need to order their bidirectional level converter and 3.3V regulator to make it work.

From the sparkfun website:

Surely they aren’t just giving irrelevant information.

Sorry for the confusion. The ADXL345 (same as this year KOP) from sparkfun is 3.3V.


thanks alot for help.

I will try the above I2C class, looks better than ours.
but then again ours was coded on a hope and a prayer seeing that we did not understand any of that low level stuff.

thanks again.

Also thanks for the analog accel link.

I’m not 100% sure, but by the looks of it (after reading the datasheet), it looks as if you’re only taking the least significant byte when reading an axis. Wouldn’t that give you a bad number? Again, I’m not sure.

Also, did this code work? I didn’t see anything wrong with it.

Code worked fine in my testing.

If you look at the getAxis method you will see that I am doing a 2-byte read when I get the data (2 consecutive registers in one read). This insures that the data does not get corrupted. If two individual 1-byte reads were performed there is a chance that in between the first and second read the data could change. This would result in first read getting the low byte of the prior value and second read getting the high byte of the subsequent value. Putting the two together again could create some really funny numbers. See page 18 of the ADXL345 data sheet “Register 0x32 to Register 0x37” section for more information about this.

Here is an example of the problem: prior value is 0x0100 subsequent value is 0x00ff, a 1 bit change. Two single byte reads would read low byte 0x00 and high byte 0x00 giving 0x0000. No where near close to what the sensor is actually reading.

Makes sense. Thanks for the code! Much easier than writing my own.


we tested this code yesterday.

but it did not work for us and since the code seems to work for u guys.
We are probably doing something wrong.

For our wiring we plugged in (obviously 5v to 5v and 0v to ground and so on) but what i have a question on is which I2C channel those plug in to. There are 2 that are not labeled, so i guess the question here is what channel I2C is the kaddress is referring to?

Also I am using the class in the code by

-instantiating with an argument of 4 (which is where the digital module is plugged in to on the crio)

-calling the initialize() method

-and then calling the getXAxis() method in my polling while loop which runs every .02 seconds.

The only thing i could see that might cause a problem is that the accel does not show a significant enough amount of change in the .02s in which we check it.

If this is what is happening please let me know and if its not please try and help.

Thanks in advance.

Here is my test program:

public class RobotTest extends SimpleRobot {
    ADXL345DigitalAccelerometer accelerometer = new ADXL345DigitalAccelerometer(4);
    public RobotTest()

     * This function is called once each time the robot enters autonomous mode.
    public void autonomous() {

     * This function is called once each time the robot enters operator control.
    public void operatorControl() {

        while( this.isOperatorControl() && this.isEnabled() )
            System.out.println("Accel X, Y, Z: " + accelerometer.getXAxis() + " " + accelerometer.getYAxis() + " " + accelerometer.getZAxis() );

Wiring should be from the I2C header on the digital side car. The I2C header is the row of 4 pins directly behind the special Lego RJ12 connector. Wire 5V to 5V, 0V to (-), SDA to SDA, SCL to SCL. Do not use the second row of pins labeled 1,2,3,&4.