1056 User Guide: Difference between revisions

Revision as of 20:41, 1 August 2012

Getting Started

Checking the Contents

You should have received:

A PhidgetSpatial 3/3/3
A Mini-B USB cable

Connecting the Pieces

Connect the PhidgetSpatial 3/3/3 to your PC using the Mini-B USB cable.

Testing Using Windows 2000 / XP / Vista / 7

Make sure you have the current version of the Phidget library installed on your PC. If you don't, follow these steps:

Go to the Quick Downloads section on the Windows page
Download and run the Phidget21 Installer (32-bit, or 64-bit, depending on your system)
You should see the icon on the right hand corner of the Task Bar.

Running Phidgets Sample Program

Double clicking on the icon loads the Phidget Control Panel; we will use this program to ensure that your new Phidget works properly.

The source code for the Spatial-full sample program can be found in the quick downloads section on the C# Language Page. If you'd like to see examples in other languages, you can visit our Languages page.

Updating Device Firmware

If an entry in this list is red, it means the firmware for that device is out of date. Double click on the entry to be given the option of updating the firmware. If you choose not to update the firmware, you can still run the example for that device after refusing.

Double Click on the icon to activate the Phidget Control Panel and make sure that the Phidget Spatial 3/3/3 is properly attached to your PC.
Double Click on Phidget Spatial 3/3/3 in the Phidget Control Panel to bring up Spatial-full and check that the box labelled Attached contains the word True. You can adjust the Data Rate by moving the slider. Move the 1056 board around and you should see the data change to reflect the change of position along the 3 axes.

Testing Using Mac OS X

Go to the Quick Downloads section on the Mac OS X page
Download and run the Phidget OS X Installer
Click on System Preferences >> Phidgets (under Other) to activate the Preference Pane
Make sure that the Phidget Spatial 3/3/3 is properly attached.
Double Click on Phidget Spatial 3/3/3 in the Phidget Preference Pane to bring up the Spatial-full Sample program. This program will function in a similar way as the Windows version.

Using Linux

For a step-by-step guide on getting Phidgets running on Linux, check the Linux page.

Using Windows Mobile / CE 5.0 / CE 6.0

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Technical Details

3-Axis Accelerometer

For more information on how to use the accelerometer, check the Accelerometer Primer.

3-Axis Gyroscope

For more information on the gyroscope, see the Gyroscope Primer.

3-Axis Magnetometer (Compass)

The magnetometer reports the sum of all magnetic fields acting on the 1056 device. The earth’s magnetic field is only one source that affects this measurement. In order to get accurate bearing data from the magnetometer - ie. to find magnetic north as a compass - any interfering magnetic effects need to be calibrated out.

Any magnetic field that is stationary with respect to the 1056 device, and less than ± 3 Gauss, can be calibrated out of the magnetic field measurement. This includes both hard and soft iron effects caused by nearby ferrous and magnetic materials. Interfering magnetic fields that vary in strength and orientation with respect to the 1056 device cannot be easily calibrated out.

Magnetic field data will become unavailable for ~28ms every 2 seconds as the compass perform internal calibrations. During this time, polling the magnetic field will return EPHIDGET_UNKNOWNVAL, or throw an UNKNOWNVAL exception. The magnetic field data in the SpatialData event will equal PUNK_DBL.

Magnetic Error Correction (Calibration)

In order to get numbers of useful accuracy from the 1056's compass you will need to provide calibration parameters. To make determining them easy, we distribute a program with our drivers that does this for you.

To calibrate your compass:

Navigate to the Phidgets installation folder on your computer. Open the 'examples' folder and find the Compass Calibrator program.

Start the program and find the link in the Settings/Status text box. Go to the website listed. (http://www.ngdc.noaa.gov/geomag-web/#igrfwmm)

Select your country and city. Click 'Get Location' and then 'Compute'. A table of values will show up in an overlaid window. The value you will need is the 'Total Field' value in nT.

Enter the magnetic field value into the calibration program.
Depending on what your application is this step as well as the next step might be a bit different. If you are intending on mounting the 1056 onto a large vehicle such as a car then you should mount the 1056 securely to the vehicle in its final intended position then check the 2-axis bubble, click the 'Start' button.
If you are using a smaller, more easily handled vehicle such as a small robot (something you could physically pick up) you will mount the 1056 and use the 3-axis calibration instead. Click 'Start'.

Rotate the compass around (including whatever equipment you have mounted it to) such that the red dots being generated on screen outline as much of a full sphere (in 3-axis) as possible. This will take several minutes. Being perfect is not necessary but try to be as thorough as time permits. Once done, click stop.
If you are in a large vehicle, you will be aiming to fill out a disc instead of a sphere. This can be done by simply driving around for a few minutes making sure to do complete $360^{o}$ turns in the process.

Take the parameters displayed in the text box and use them for your compass. For example in C#:

 
     setCompassCorrectionParameters(0.51075, 0.18820, -0.07456, -0.02209, 1.87163, 1.87640, 2.12565, -0.04000, -0.04084, -0.03552, 0.09073, -0.04258, 0.11056);

API

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Data Structures

SpatialData {

double acceleration[3];

double angularRate[3];

double magneticField[3];

Timestamp time;
};
Timestamp {
int seconds; -time since attach event

int microseconds; -time since last second

};

The SpatialData Structure is used by the OnSpatialData event. This contains acceleration data, angular rate data, magnetic field data, and a timestamp. The timestamp is an accurate measurement streamed from the hardware,and can be trusted over a local software timestamp. This timestamp is generally used for integrating angular rate into a heading over time.

Product History

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-====Finding North====
-The three axis magnetometer data can be used, along with pitch and roll angles calculated from the accelerometer, to find a magnetic bearing - ie. as a compass. In order for the compass to be accurate at all, calibration must have been done to factor out hard and soft iron offsets.
-The magnetic field is represented as a vector. If the 1056 is completely level with respect to gravity, then we can calculate magnetic bearing easily by looking at the x and y components of the vector, which simply represents an angle between 0 and 360 degrees on the unit circle.
-However, when the board is not level, the magnetic field vector components in each axis will be skewed, or is other words, what we need to know is the magnetic field with respect to the earth frame, and what we have is the magnetic field with respect to the 1056, which is rotated with respect to the earth. What needs to be done is to rotate the magnetic field vector back into the earth frame, we can then use the x-y components to again determine bearing. The easiest way to do this is to find the board pitch and roll angles using the accelerometer, and then build a rotation matrix using these angles to rotate the magnetic field vector into the earth frame (ie aligned with gravity). This is demonstrated in the C# and Cocoa examples.
 ====Further Reading====

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