IFD:Sensors

Sensors can be categorized by many aspects. Intuitively the most unique property of a sensor is what's it obviously detecting. For example everybody would know that a temperature sensor is measuring the physical temperature. And also what an air pressure sensor is made for. In these examples the physical method and our common understanding of the sensor is identical.

However there are also sensors which aren't that obvious. What is a touch screen measuring? Touchscreens are detecting touch, but they are measuring pressure or presence - or even resistance or capacitance. So the touch screen is more an applicance of an other type of sensor.

Many technical related people will regard the physical method of measurement as most clearly identifying. However this isn't true as well as there are many sensors which are already a fusion of many sensors. (for example an inertial motion unit has a compass, gyroscopes, temperature sensor and and accelerometer). Thus it can be very hard to find a specific sensor.

To design electronic devices using a sensor the electric interface of the sensor plays a main role in using- and sometimes also when selecting a sensor. Some are very simple to interface and need almost no effort, while others are very precise and need a special interface.

All three: application, physical method and electric interface are important - and there may be more properties to categorize sensors.

Interfaces

Sensors can be interfaced via:

• Resistance
• voltage
• current
• capacitance
• frequency (pulses per time)
• digital protocols (serial and parallel)
• pwm (lenth of on/off period - duty cycle)
• switch (connection is open and closed)
• open collector (almost identical to a switch)
• logic level (high / low)
• other...

Physical property measured

• Pressure or Tension
• Voltage
• Current
• Magnetism / magnetic fields
• Bend / flex / Radius / curvature
• Position
• Length / distance
• Presence
• Orientation
• Light
• Conductance (resistance)
• Sound / ultrasound / air pressure
• Sound in fluids or pressure in fluids
• Shear
• Angle

Applications

Uncountable - thus incomplete:

location (2d, 3d), eye position, movement, forces and deformation, presence, ambient measurements. switches and buttons. incremental input (rotary or linear sliders, etc.)

Common Examples

• tablet writing: location + pressure
• mouse: location + digital pressure + wheel
• touch screen
• inertial tracking
• GPS tracking
• Joystick
• Piano Keyboard

List of Sensors

Sensor	Physical	Electrical
Bend and flex stress or curvature	Bending	Resistive
Reed switch	Magnetism	Switch
Photo transistor	Light, broad spectrum	Transistor, current
Photo diode	Light, broad spectrum	Diode, reverse current
LDR (Light dependant resistor)	Light, broad spectrum	Resistive
PIR: passive infrared movement detector	Movement of differently warm objects	Open collector / Voltage / Switch
Pyroelectric Sensor	Changes in Temperature	Transistor, current
FSR Force sensing Resistor	Pressure	Resistive
NTC	Temperature	Resistance
PTC	Temperature	Resistance
Temperature Sensor, integrated	Temperature	Voltage
Hall Sensor	Magnetic fields	various.
Electret microphone	Pressure (sound) in air.	Voltage (integrated amplifier)
Piezo disk or transducer	deformation, sound in solids and fluids,	Voltage
Strain gauge	Pressure and tension	Resistance
Peltier element	Temperature difference bewtween 2 surfaces	Voltage + Current
Vibration Sensor (piezo)	Acceleration (by inertia)	Voltage
MEMS Acceleration Sensor	Acceleration	PWM
Rotary encoder	Rotation, infinite	Switch
Rotary encoder	Rotation, infinite, absolute	Open collector, digital
Potentiometer, rotary	Rotation, limited
Potentiometer, hotpot	Pressure	Resistive
Potentiometer, slider	Linear position	Resistive
Touch, Capacitive (Button)	Presence	various
Touch, Capacitive (Slider)	Position and Presence	various
Touch, Capacitive, 2D	Position 2D and Presence	various
Touch, Resistive, 2D	Position 2D and Pressure	various
CCD array	Light	digital or analog video
Stepper motor	rotation, infinite	Voltage, digital (pulses)
Sharp Distance Sensor (IR)	Distance	Voltage
Ultrasonic Distance Sensor (Parallax Ping)	Distance (to parallel surface)	digital

Links

http://www.rn-wissen.de/index.php/Sensorarten