Sensors and platforms

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Sensors and platforms

• CUCL

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Overview

• CUCL experience
• Inertial and pressure sensors
• Wireless platforms
• Initiate discussion
• What further types of sensors are worthy of
  evaluation
• System requirements for wireless sensor platform

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Inertial Measurement Unit (IMU)

• 3D gyroscopes, 3D accelerometers, digital compass
  (magnetometer)
• Measurements
• Linear acceleration (3D)
• Rate of turn (3D)
• Direction of sensor relative to the magnetic
  north
• Output (derived results)
• 3D orientation (e.g. Euler angles) more
  accurate
• 3D translation not accurate
• Key parameters
• Stride length (SL) and Stride frequency (SF)
• Acceleration curve over 100m
• Rotation and translation of body parts
• Approximate costs
• Full IMU Xsens MTX 1000
• Separate components around US 10 each but
  mounting them is an issue

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Inertial sensor
XSens MTX
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Inertial sensor

• Running and stepping on tape markers (1m apart)

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Force sensors

• Force Sensing Resistors (FSR)
• Decrease in resistance with an increase in the
  force applied to the active surface.
• Cost 50 for a development kit with 16 sensors

Active area
Tail
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Sentient Sports Shoes
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Wireless platform and sensors

• Wireless sensor node (Tmote)
• 250kbps 2.4GHz IEEE 802.15.4 (Zigbee)
• 8MHz MSP430 microcontroller
• Integrated 12-bit ADC
• Software development in TinyOS

• 3 force sensors 0.5" diameter (middle and front
  part of foot)
• 1 force sensor 1.5" square (heel)
• 1 inertial unit with 3D accelerometers, 3D
  gyroscopes, magnetometers

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Preliminary Experiments

• Jogging 50 meters
• Expected pattern of applied forces
• Heel Left side impact absorption
• Right side Toe generates impulse for the next
  stride
• Not yet interested in the magnitude of forces
• Real-time data gathering

Toe
Right
Left
Heel
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Preliminary Results
Heel, left, right, toe
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Bend Sensors / Optical-based

• ShapeTape - thin flexible ribbon which measures
  the attitude of the tape at various positions
  along its length.
• Evaluation of the ShapeTape Tracker for Wearable,
  Mobile Interaction
• Yohan Baillot, Joshua J. Eliason, Greg S.
  Schmidt, J. Edward Swan II, Dennis Brown, Simon
  Julier, Mark A. Livingston, Lawrence Rosenblum,
  Virtual Reality Laboratory, Naval Research
  Laboratory, Washington D.C.
• Conclusion ShapeTape is not appropriate for
  interactions which require a high degree of
  accuracy. However, ShapeTape is capable of
  reproducing the qualitative motion the user is
  performing and thus could be used to support 3D
  interaction.
• Cost range of 1000 - 2000

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Bend sensor / Resistance-based

• Resistance proportional to the degree of flexing
  and bending
• Coated substrate, such as plastic, that changes
  in electrical conductivity as it is bent
• Cost 40

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Distance Sensor/Proximity

• Sharp GP2D12
• Measure distance between itself and an object
  that is within a distance range of 10cm (4") to
  80cm (30")
• Cost 15

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Pulse Oximeter (SpO2)

• Indicates the percentage of hemoglobin molecules
  in the arterial blood which are saturated with
  oxygen.
• Approach measures the amount of red and infrared
  light received by the detector and calculates the
  amount absorbed
• Two options
• Dolphin clipper sensor (Imperial College)
• Smaller the BCI Medical Micro-Power Pulse
  Oximeter, measuring 39 mm 20 mm with a current
  draw of just 6.6 mA at 3 V.
• They also measure heart rate

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Other physiological sensors

• ECG
• EMG
• Breathing rate

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Issues

• Size and wearability of sensor nodes
• System integration
• Drift over time - inertial sensing
• Body sensor network
• Realtime
• High sampling rate
• High volume of data
• Aggregation and compression on board
• Network of 5 inertial Xsens Mtx units
• Magnetometer gyroscope accelerometer
  timestamp
• 9 fields x 32B 32B 320 Bytes (Calibrated
  inertial and magnetic data)
• Header 40 Bytes
• ?Sampling Rate 100 samples/second
• Total throughput (320 40) x 100 x 5 nodes
  1.44 Mbps
• Throughput issue for wireless (ZigBee, Bluetooth,
  etc)