Sungmin Kim
SEOUL NATIONAL UNIVERSITY
Smart Garment Design
6. Sensors and Actuators
Sensors Basics
Definition of Sensor
Electronic component that measures some aspect of the physical world
– Light– Movement (Position/Velocity/Acceleration)– Temperature– Touch
Converts the aspect into varying electrical characteristics
– Voltage – Resistance
Importance
Make the physical world perceivable by computers
– microcontrollers
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Sensors Selection Guide
Connector
Type
– Male header ↔ Female header– Breadboard spacing ↔ Something else– Standardized plug ↔ Proprietary connector specific to the manufacturer
Importance
– Determine what other materials you will need to build your circuit
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Legs, terminal, JST connector, pins, hook, male headers
Sensors Selection Guide
Sensitivity
Range of values your sensor senses
– Small force-sensing resistors (FSRs) : 2g– Large force-sensing resistors : 100g ~ 10kg
Accuracy
FSRs are very sensitive but not always accurate
– Provide good answers to questions like, “Is this being pressed or not ?”– Do not provide the level of accuracy needed for building a food scale or body scale
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Sensors Selection Guide
Form Factor
Shape, size, and weight greatly affect how a component can be worn on the body
Look at dimensions and technical drawings to determine if a sensor will fit in your design
Output
Information provided by a sensor
– Varying voltage– Varying resistance
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Flex sensors in different sizes
Desk Lamp
Sensors Working with Sensor Data
Threshold
Used to set a boundary between one condition and another
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Dark
Light
1023
200
0
Dark
Light
1023
200
0
500
For an example of light sensor (0~1023)
Sensors Working with Sensor Data
Mapping
A way to translate a value from one range of numbers to another
Used to create a direct relationship between an input and an output
– Control the brightness of an LED using light sensor output
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Sensors Working with Sensor Data
Calibration
The range of what a sensor senses will differ based on its environment and context
Determination of the highest and lowest values is important
Smoothing
Some sensors produce data that’s rougher around the edges
Smoothing can help turn an erratic data stream into cleaner and easier one to work with
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Sensors Working with Sensor Data
Data Handling
Wireless communication
– Bluetooth
– Zigbee
– Wi-Fi
– NFC (Near Field Communication)
Integrated storage
– Micro SD card
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Sensors What to Sense
Heart Rate
Optical heart rate sensors measures the mechanical flow of blood in a finger or earlobe
– LED shines light into the capillary tissues and a light sensor reads what is reflected back
Chest strap heart monitors are more expensive but more accurate solution
– Measure the actual electrical frequency of the heart through conductive textile electrodes
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Sensors What to Sense
Glavanic Skin Response (GSR)
Measures the conductivity of the skin
– Changes in this conductivity can indicate a response to physical or psychological stimulus
– Used for classic lie detectors
Electromyography (EMG)
Measures the muscle activity by detecting its electrical potential
– Used for artificial exoskeleton
Electroencephalography (EEG)
Measures the electrical activity in the scalp
– Headsets are used in thought controlled computing applications
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Sensors What to Sense
Flex
Flex sensors sense a flex or a bend
Very good for areas of the body that bend in a broad, round arc
– Elbows, knees, fingers, and wrists
Factors to be considered are:
– Length– Directionality
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Sensors What to Sense
Force
Force-sensing resister (FSRs) are used to sense touch
Different types are suited for different applications
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Sensors What to Sense
Stretch
A conductive rubber cord whose resistance decreases the more it gets stretched
Movement, Orientation, and Location
Accelerometers for changes in speed of movement
– Inside-out tracking
Tilt switch for orientation
GPS module for location
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Sensors
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What to Sense Motion
Visual tracking sensor
– Outside-in tracking
Sensors What to Sense
Light & Color
Photocell’s resistance varies based on the level of light it senses
Color is hugely important in the worlds of design and fashion
Sound
Sounds can provide significant clues about what is going on around you
A simple microphone can act as a great sensor for audio-reactive projects
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Sensors What to Sense
Proximity
Used for detecting nearby objects, walls, or even other people Types
– Infrared (IR) type» Sensor sends out a beam of infrared light that bounces off the object and measures it» Less expensive but easily tricked by heat or sunlight» Shorter, more focused distance ranges
– Ultrasonic type» Sensor sends out ultrasonic sound that bounces off the object and measures it» The proximity is determined by the length of time it takes for the sound to return» More expensive but harder to trick
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Sensors What to Sense
Proximity
Types– LIDAR (Light Detection and Ranging)
» Illuminates the target with pulsed laser light and measures the reflected pulses with a sensor» Differences in laser return times and wavelengths can make digital 3-D representations of the target» Applied to terrestrial, airborne, and mobile applications
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Sensors
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What to Sense Shape
Laser displacement sensor
Sensors What to Sense
Temperature
Temperature sensors can be used to sense both environmental conditions and body warmth
A thermistor (variable resistor) is the easy place to start
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Sensors Textile Based Sensors
Tilt Potentiometer
Petals are connected through a series of fixed resistances
Depending on which petal the metal bead rests on, the analog reading will be unique
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+ -A
Sensors Textile Based Sensors
Woven Pressure Sensors
The honeycomb weave creates 3D structure when taken off from the loom
– Separates the yarn when not pressed– Gives a nice bouncy feedback when pressed
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Sensors Textile Based Sensors
Woven Pressure Sensor Matrix
Interweaving layers of conductive/non-conductive fabric and velostat
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Sensors Textile Based Sensors
Zipper Switch
A zipper is a great clothing material that can be converted into sensors
Zipper switch is a known technique used in many projects
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Sensors Textile Based Sensors
Neoprene Bend Sensor
This sensor actually reacts to pressure, not specifically to bend
Bend angle can be measured indirectly by pressure exerted while bending
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Actuators Light
Basic LEDs
Through-hole LED
– Easy to handle and prototype
Surface mount LED
– Tend to integrate more delicately with garment
LED String/Strip/Ring...
– Control a large number of LEDs easily
RGB (Red, Green, Blue) LED
– Lights in multiple colors
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Actuators Light
Adressable LEDs
Ex) Flora NeoPixel
– Used in combination with the Flora main board– Connections including power, ground, and signal– Connected multiple LEDs can be addressed individually
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Ampli Tie
Actuators Light
Fiber Optics
Flexible, transparent fibers that can transmit light
– LEDs are often used as light source
Used for many applications
– Sophisticated high speed communication – Magical light-up wands
Types
– End-glow– Side-glow
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Luminex fiber optic fabric
Actuators Light
Electroluminescent Materials
Emit light when current is applied
– Consist of a conductor (such as copper) coated with phosphor– Comes in the form of a wire, tape, or panel
Attractive because they provide a large, consistent
surface area of light different from LEDs
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Syuzi Pakhchyan's 'Tron: Quorra Costume"
Actuators Sound
Factors to be Considered for Garment Application
Type of sound
– Simple beep, tone, or audio file
Triggering method
Place of sound-emitting device
Loudness of sound
– Intended only for the wearer or nearby people
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Actuators Sound
Simple Sound
Buzzers
– Simple way to provide audio feedback– Create an audible sound as the result of a electrical signal
Types
– Electromagnetic buzzers» Creates noise when continuous voltage is applied
– Piezoelectric buzzers» Require an oscillating signal and function much like speakers
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Actuators Sound
Tone
Speakers
– Produce a broader range of sounds– Generate specific notes using a microcontroller
Audio Files
Ex) LilyPad MP3 board
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'Bio Circuit' by Dana Ramler and Holly Schmidt
Actuators Sound
Fabric Speaker
Same principle with conventional speaker
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Actuators Motion
Vibrating Motors
Vibrational feedback can be powerful, subtle, and even seductive
Vibration can simulate a stroke, a tap, or a tickle
Ideal for some situations:
– Inconvenient or impossible for the wearer to see or hear feedback
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Actuators Motion
Servo Motors
Capable of accomplishing small, discrete movements
Extremely precise in their position
Can be told to turn to any location within its potential range of movement
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Medium servo
Micro servo
Actuators Motion
Linear Servo Motors
Convert rotation into linear motion
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Actuators Motion
Gearhead Motor
A DC motor spins freely and quickly when voltage is applied
A DC motor augmented with a set of gears that reduce the RPM (revolution per minute)
A gearhead motor tends to be much stronger than a typical servo motor
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'Short++' by Adi Marom
Actuators Motion
Smocking Fabric
Use SMA (Shape Memory Alloy) to actuate fabric into a smocking pattern
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Actuators Motion
Electromagnetic Velcro
A coil becomes a magnet and gets attracted to a magnet when electricity is applied
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Actuators Motion
Flip-Dot Fabric
A coil and a permanent magnet are used for flip-dot effect
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Actuators Temperature
Cooling
Small fans are used
Heating
Thin electric heating pads are used
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Actuators Temperature
Thermoelectric Cooling & Heating - Peltier Effect
Principle
– Create a heat flux between the junction of two different types of materials
– Transfers heat from one side of the device to the other using electrical energy
Advantages
– Lack of moving parts or circulating liquid
– Very long life
– Invulnerability to leaks
– Small size and flexible shape
– Can be used as a thermoelectric generator
Disadvantages
– High cost
– Poor power efficiency
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