IoT Sensors - Optical Sensors

Measurement of electrical resistance by converting a change in incident light into a change in electrical resistance; where the material becomes more conductive due to absorption of electromagnetic radiation (e.g., visible, ultraviolet, infrared, or gamma radiation). When a photoconductive material is connected as part of a circuit, it acts as a resistor whose resistance depends on the light intensity. In this case, the material is called a photoresistor (also known as a photosensitive resistor or photoconductor)

The cell is a large bare diode, built using a pn structure between appropriately doped semiconductors. Photons striking the cell pass through the thin p-doped layer and are absorbed by electrons in the n-doped layer. This leads to the creation of conduction electrons and holes

A photodiode is a light junction device. It is an ordinary diode whose PN junction is exposed to light through a transparent case or transparent lens. These diodes have the same voltage-current characteristics as any other junction diode. However, they have higher conductivity than conventional diodes.

Photodiodes are sensitive to both visible and infrared light. The biggest disadvantage of photodiodes is that their reverse leakage current remains in the microamp range - even in light. Therefore, they require operational amplifier circuits for light detection.

Photodiodes have response times measured in nanoseconds. They are used in sophisticated applications including cameras, imaging and scanning equipment, CD and DVD readers, fiber optic communications, motion detection and positioning sensors.

PIR (passive infrared sensor ) Sensors are passive devices that detect changes in infrared radiation without generating or radiating any power themselves. This allows them to operate reliably over long periods of time (up to 20 years) with very low power consumption. They require only a small amount of heat input from an external heat source (e.g. the sun, humans, appliances, etc.) to operate.

The PIR is a passive motion detector that waits for infrared temperatures from body temperature to trigger activity. In other words, it senses motion through temperature changes

Phototransistors are similar to photodiodes except that they amplify current. These are usually designed using a common NPN transistor with a collector-base PN junction exposed to light through a transparent case or transparent lens. Due to current amplification, their output current is 50 to 100 times that of a photodiode. The base region is galvanically isolated or has a sensitivity control.

Phototransistors are commonly used as optical switches, optical isolators or infrared filters, as well as for infrared remote controls and fiber optic communications.