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 | analog / digital voltage. |
| 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 / Analog voltage, i2c, ... |
| 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) |
| Infrared (IR) Distance Sensor (Sharp) | Distance | Voltage |
| Ultrasonic Distance Sensor (Parallax Ping) | Distance (to parallel surface) | digital |