2010 Accelerometer I2C Object/Class

[jhersh]

Originally Posted by NerdGuy

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.

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

Originally Posted by NerdGuy

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?

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

[NerdGuy]

does anyone know where to buy the Analog Accelerometer Breakout ?

[jhersh]

Originally Posted by NerdGuy

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/pro...roducts_id=849

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

-Joe

[charrisTTI]

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;

    // DATA_FORMAT
    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) {
            super(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;
                break;
            case DATA_FORMAT_04G:
                returnValue *= 4.0;
                break;
            case DATA_FORMAT_08G:
                returnValue *= 8.0;
                break;
            case DATA_FORMAT_16G:
                returnValue *= 16.0;
                break;
        }
        return returnValue;
    }
}

[Geek 2.0]

Originally Posted by charrisTTI

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;

    // DATA_FORMAT
    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) {
            super(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;
                break;
            case DATA_FORMAT_04G:
                returnValue *= 4.0;
                break;
            case DATA_FORMAT_08G:
                returnValue *= 8.0;
                break;
            case DATA_FORMAT_16G:
                returnValue *= 16.0;
                break;
        }
        return returnValue;
    }
}

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.

[charrisTTI]

Originally Posted by Geek 2.0

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.

[Geek 2.0]

Originally Posted by charrisTTI

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.

[NerdGuy]

/sigh

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.

[charrisTTI]

Here is my test program:

public class RobotTest extends SimpleRobot {
    ADXL345DigitalAccelerometer accelerometer = new ADXL345DigitalAccelerometer(4);
    
    public RobotTest()
    {
        accelerometer.intitialize();
        accelerometer.setRange(ADXL345DigitalAccelerometer.DATA_FORMAT_16G);
    }

    /**
     * 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() {
        this.getWatchdog().setEnabled(false);

        while( this.isOperatorControl() && this.isEnabled() )
        {
            System.out.println("Accel X, Y, Z: " + accelerometer.getXAxis() + " " + accelerometer.getYAxis() + " " + accelerometer.getZAxis() );
            Timer.delay(0.001);
        }
    }
}

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.

[Geek 2.0]

Originally Posted by charrisTTI

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.

This is what he means (took me a bit to figure it out without the DSC in front of me, so I thought I'd make a visual aid).

[NerdGuy]

possibly the most helpful post Ever.

I will try this in about an hour and post the results we were on the ones labeled not these.

Also i am curious what the pins labeled not these are for?
It says "Out" does that just mean those are all Digital Outputs?


Thanks again

[jhersh]

Originally Posted by NerdGuy

Also i am curious what the pins labeled not these are for?
It says "Out" does that just mean those are all Digital Outputs?

They are slow digital outputs (kinda like the Spike output channels). We never bothered to add support for them in WPILib, but there is support for them in the FPGA and the FPGA chip object layers. Teams technically could use them, but we don't know why they would.

-Joe

[charrisTTI]

Originally Posted by jhersh

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/pro...roducts_id=849

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

-Joe

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.

[jhersh]

Originally Posted by charrisTTI

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:

Originally Posted by SparkFun

The ADXL320 can be powered from 2.4V-5.25V.

Surely they aren't just giving irrelevant information.

[charrisTTI]

Originally Posted by jhersh

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.