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Clever Pointer Device

Samer AamarPost PC Course – 2002

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It would be great to be able to…

move next/previous without the need to be near your PC/Laptop

mark important words / draw basic shapes (circles, arrows, etc.) with his pointer device

press on buttons on the screen, activate shortcuts, surf in WEB…

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Well, sounds like a

Mouse!

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How does it work?

The pointing device will plot a virtual ray! The intersection with the projection screen

will be calculated (3D space) The computer will translate the intersection

3D point into a 2D point on the screen. Mouse Move events will be fired to the

system

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xx

y/yy = h/hh x/xx=w/ww

w

h

x

y

ww

hhyy

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Some mathematics

The points p1, p2 are in 3D space The ray vector p2-p1 It would be easy to calculate the intersection point with the

screenBUT, before all

the coordinates of the projection screen should be defined

p1 p2

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Components

Basic components:

2 Tri-Axis Accelerometers

Three buttons

Transmitter/Receiver (wireless)

3D Accelerometers

buttons

Transmitter

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Buttons

The device has three buttons: ‘Activate’ button:

When down the MOUSE_MOVE event is fired

‘LButton’ / ‘RButton’ button: samples the Left/Right Button on the regular

mouse

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Press On Activate

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Press On Activate

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Hold Activate and Move Pointer!

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Release Activate button!

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Release Activate button!

Press on LButton/RButton

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Accelerometers

We need: 3-Axis Accelerometer

MEMS (Micro Electro Mechanical Systems) Acc. :SmallLight

Ability to measure hand motion (next slide)

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Measuring Hand Motion

Parameter Target Value

Frequency Range 0.1 to 25 Hz

Acceleration Amplitude +/- 5 g

Acceleration Resolution 1 mg

g ~ 9.8 m/sec2

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Accelerometers (II)

Good enough (according to the sheets)

Analog Device iMEMS accelerometers ADXL105 ADXL150

Microsystems Technology Laboratory (MTL) 3-Axis accelerometers:

TG Series Accelerometers: CXL10TG3 (crossbow tech.) ACCELEROMETERS by Vernier

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Analog Devices Performance

Resolution of ADI accelerometer sensors over

time

Cost of performance in ADI accelerometer sensors

over time

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Relevant Thesis

Graham B.; Using an Accelerometer Sensor to Measure Human Hand Motion; Massachusetts Institute of Technology; 2000.

He achieved the following: Frequency: 0.1 – 25 Hz Amplitude: ±10g Mass: 4.88 grams Size: (17mm)^3

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Transmitter/Receiver

Frequency: 25 Hz

Data (bits): 2 x 3 x 32 (X, Y, Z) 3 (buttons)

Total (per second)25 x 194 = 4850 = 4.8 Kb per sec

PossibilitiesBluetooth – too much!Radio transmitter/receiver – simple: 10 Kb per sec is OK!

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Summary

Required Existing

3-Axis Accelerometers

Three single-axis accelerometers (Analog Devices)

Receiver/Transmitter Radio

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Open Issues!

CPU Consuming? Sudden movements – like sharply putting the

device on the table (20g) What happens if the connection between

transmitter and receiver was interrupted temporarily for some reason (example by moving to another room)

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Related Sites

http://www.analog.com http://shop.store.yahoo.com/crossbow/index.html http://www-mtl.mit.edu/MEngTP/Graham_Thesis.pdf

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END