You may have learned the generalized IoT structure. The building blocks for Things(Devices) are made of all kinds of Sensors and Actuators. The sensors are used to collecting data from device’s immediate environment that transfer into meaning intelligence for the automation system to give directions to actuators to achieve smart operation. An actuator, on the other hand, can be seen as a tool which functions inversely to the sensor. There are varied types of sensors that can be incorporated into IoT systems. we are going to look at major types of sensors used in IoT applications.
IoT device or Things are embedded with sensors, software and other technologies for the purpose of connecting and exchanging data with other devices and systems over the internet.
A sensor is a device or module, machine or subsystem whose purpose is to detect events or changes in environment and send the information to other electronics device. As the bottom layer of the IoT system, sensor should be easily connect to network layer directly or indirectly via other devices. A reliable sensor can be a standalone module or devices embedded into objects(such as lighting fixtures).
Visible Light Sensor, it can be used to detect ambient light intensity. It could be as simple as photo-resistor that resistance change with the intensity of light.
Temperature and Heat Sensor, it used very widely where keeping track of thermal conditions is needed. It could be a Thermistor whose resistance change correlated to ambient temperature. Negative Temperature Coefficient (NTC) thermistors exhibit a decrease in electrical resistance when subjected to an increase in body temperature and Positive Temperature Coefficient (PTC) thermistors exhibit an increase in electrical resistance when subjected to an increase in body temperature.
Moisture Sensor, modern hygrometers includes Capacitive or Resistive. Capacitive hygrometers is through measuring the effect of humidity on the dielectric constant of a polymer or metal oxide material, and it is subject to drift and aging effects. The resistive hygrometers is measuring the change in electrical resistance of a material(salts or conductive polymers) due to humidity. since the material property also depend on temperature, the sensor typically combines with a temperature sensor.
Motion Sensor, it can be divided into a few different types based on its technology: Passive Infrared (PIR) Sensor, Ultrasonic Sensor, Microwave Sensor.
The most simple PIR sensor include a thin Pyroelectric film material that responds to Infrared radiation by emitting electricity. It typically works with a Fresnel lens that help converge the Infrared radiation emitted by target object to the sensor surface area.
Ultrasonic sensor can be active or passive. Passive ultrasonic motion sensor listens to certain frequency of sounds such as glass breaking or metal on metal. Active ultrasonic sensor usually comprise a pair of devices, the transmitter generates sound waves at higher frequency 30KHZ to 10MHZ,the receiver capture the reflected sound waves and analyze it to detect people presence in the space.
Gyroscope Sensors, also called Angular Rate Sensor or Angular Velocity Sensors, it can be utilized to sense angular velocity and measure motion of the object. For more robust and accurate motion sensing, in consumer electronics Gyroscope sensors are combined with Accelerometer sensors.
Image Sensor, where photons are captured as charged electrons and silicon and converted to a voltage value through the use of capacitors and amplifiers, then later transferred into digital code which can be processed by a computer. Two major types of image sensors based on different way to process stimuli.
CCD( Charge Coupled Device), pixels are represented by P-doped Metal Oxide Semiconductor(MOS) capacitors. CCD senor can capture images with lower noise than CMOS. It also works better in low light.
CMOS(Complementary Metal Oxide Semiconductor), its primary advantage over CCD sensor is less expensive to produce and consume less power than CCDs. it typically combine the image sensor function and image processing into same IC. It has rolling shutter issues with more digital noise.
Chemical/smoke/gas Sensor, that can detect chemical compounds (solids , liquids, gases) are very important to industrial security and environmental protection systems. There are two main steps involved in the functioning of a chemical sensor, recognition and transduction. Screen printed electrochemical sensor technology can be used to detect CO gas.
For smoke detector , there are few different technology from Ionization to Photoelectric (optical). An ionization smoke detector uses a radioisotope, typically americium-241, to ionize air; a difference due to smoke is detected and an alarm is generated.
A photoelectric, or optical smoke detector, contains a source of infrared, visible, or ultraviolet light — typically an incandescent light bulb or light-emitting diode (LED) — a lens, and a photoelectric receiver — typically a photodiode. The light emitted by the light source passes through the air being tested, and reaches the photosensor. The received light intensity will be reduced due to scattering from particulates of smoke, air-borne dust, or other substances; the circuitry detects the light intensity and generates the alarm if it is below a specified threshold, potentially due to smoke.
This is an just a brief overview of some of the most common IoT sensors that already play a key role in our life. Most of these sensors are small size and very efficient in collecting the relevant data to feed up to the connected smart devices that final enable the over the cloud application that we are using at mobile devices. They are truly the foundation for the success of the IoT system.