SmartArt - AD405 - Drew Browning

Sensing Movement

Body position and movement – natural everyday interaction

Installations can take advantage of this by detecting position, orientation and movement.

Assessing the need

• Position – XYZ location
• Right hand rule – positive axis direction and rotation
• Orientation – XYZ rotation
• X/Y plane – front or top view
• Movement. – change in either position or orientation
• Velocity - how fast
• Absolute vs. relative – absolute coordinates or relative to last position
• Identity – distinguish between multiple objects moving
• Degrees Of Freedom (DOF) – XYZ position/orientation
• Range of sensitivity
• Minimum/maximum/angle
• Number of interactors
• Consider constraining the space rather than more, bigger, better tech

How Ranging Sensors Work

• Emitter/detector – energy sent out to target, amount returned is measured
• Transduction – the difference between amount sent and returned is transduced
• Energy – light, sound, magnetism
• Homebrew vs. commercial sensors – cost/time

Detecting Presence or Motion – whether in/out or position change in space

· Digital input – User presence not attention

• Foot switches – cover with rug/carpet
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• Photoelectric switches – light beam make or break switch
• 
• Motion detectors – detects changes in infrared light within a space
• Passive InfraRed (PIR) sensors
• Magnetic switches
• 
• sense position of objects semi-wirelessly
• magnetism makes or breaks the switch
• Hall effect sensors – read magnetic fields, digital or analog types
1. 
• Electronic Windows – installation doc
• Burglar alarm tech – use off the shelf or hack commercial products

Determining Position – distance/direction in space

• Optical - IR Sensors – short range (1.5” – 56”), cheap
• photoresistor

• IR emitter

• IR receiver

• PIR

• Ultrasonic sensors – medium range (6” – 35’)
• MaxSonar-EZ1
• Parallax Ping sensor

• Hall Effect sensors – very short range (less than 1.5”)
• 
• GPS – very long range (global – few meters)
• GPS Shield (http://www.ladyada.net/make/gpsshield/index.html)
• RFID
• Parallax RFID
• RFID shield-kit (http://tinker.it/now/2008/09/08/tinker-it-rfid-kit/)

• Bluetootth
• bluetooth-shield (http://blog.makezine.com/archive/2008/10/arduino_bluetooth_shield.html?CMP=OTC-0D6B48984890)
• Parallax Bluetooth Module

• WiFi
• WiFi Shield (http://www.littlebirdelectronics.com/products/little-bird-brain-arduino-wifi-shield)
• 6DOF Tracking – magnetic, optical, ultrasonic, precise, medium range (10’ max)
• CWALL tracker
• 
• 

Determining Rotation – orientation in space

• Potentiometers –
• 
• mechanical rotation
• typical pot less than 360 degrees of rotation
• multi-turn and endless pots available
• Accelerometers –
• Tri-Axis
• Dual-Axis
• change in speed or movement
• 2 or 3 axes
• cannot read vertical access rotation
• tilt relative to gravity
• 90 degrees of sensitivity
• Pan – installation doc

• Compass – orientation relative to earth’s magnetic field, slow
• 
• Slip Rings – power and communication to rotating objects (motor commutation, VCR)
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• Encoders – mechanical/optical sensor tech
• Encoder wheel with slots for IR emitter/detector
• Computer count pulses
• Mechanical mouse – x/y encoders
• Rhino robot example
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Speed of Rotation

• Tachometer – RPM, bicycle tachs
• Gyroscopes - angular acceleration or change in rotation (gyro-mouse)

Video Tracking

• Video camera like array of thousands of photocells
• Lens to focus and scale the light
• Iris to control amount of light
• Separates light by color
• Computer vision
• Ability to track color – GEM: pix_blob
• Difficulties - changing light, noise, object recognition
• Humans can deal wit these issues effortlessly
• Constrain the environment to make the task easier
• Lighting
• bright, evenly lit space best for low noise
• infrared (IR) - best for motion tracking
• fluorescents - no IR
• incandescents and sun - give off IR
• Camera types
• webcams - USB and Firewire
• network cams - ethernet and composite
• DV cams
• manual controls good - iris, zoom
• Fast processor necessary - most microcontrollers too slow

Identity

• GEM: pix_multi-blob
• Barcode readers
• RFID – Radio Frequency Identification
• Magnetic card swipe