OPTOELECTRONICS


Optical Sensors T


heir primary function is to convert light into an electrical signal. This process enables the measurement and control of physical quantities such as distance, speed, position and presence.


How do Photosensors Work? Photosensors operate based on the photoelectric effect, where photons (light particles) incident on the sensor’s surface generate electrons and create an electric current. The amount of current generated is proportional to the intensity of the incident light. Different materials and sensor designs are used to optimise the photoelectric effect. There are several types of photosensors, each type having unique properties and 


Photo Detectors:


These are sensors that detect light and convert it into an electrical signal. They are fundamental components in everyday  Photodiodes generate a current when exposed to light and they are used for high-speed and low-light-level detection. Phototransistors are similar to photodiodes but have an internal gain, making them more light-sensitive.





These sensors detect an object’s presence or absence by measuring the amount of  of an emitter, usually an infrared LED and a photodetector, typically a phototransistor or photodiode, placed in proximity to each  nearby object and the photodetector detects   light changes, triggering a response from the sensor. This change in the intensity of the  absence or proximity of an object.


Ambient Light Detectors:


These sensors are designed to measure the intensity of ambient light in an environment. They typically mimic the human eye’s response to different light levels and colours,


providing a measure corresponding to a human’s perception. Usually, they consist of photodiodes or phototransistors that are sensitive to visible light and convert the ambient light intensity into an electrical signal that can be used to adjust the brightness of displays or control lighting levels.


Touchless Sensors:


These devices are a kind of alternative switch and provide a digital output signal. They detect an object’s presence, proximity or gesture without requiring physical contact with the panel or buttons. They are increasingly used in applications where hygiene or convenience is a concern.


Position Sensors:


They are also called optical encoders and detect an object’s position, direction or movement in relation to a reference  systems, ensuring precise movements and operations in a variety of devices. Nisshinbo Micro Devices has recently introduced two    precise measurements in applications requiring monitoring on a smaller scale. These encoders integrate a high-power infrared LED, four photodiode sensors and a 


Optical encoders work by using a disk or    back to the photodiode sensors. The sensors  which are then processed to determine the movement characteristics, such as speed or direction.


The advantage of optical encoders is that they are non-contact sensors, meaning they do not physically touch the moving part. This design minimises wear and tear, resulting in a longer lifespan and higher reliability. 


high-resolution measurements, which are crucial in applications requiring precise control, such as robotics, industrial automation and computer peripherals.  examples of “quadrature” encoders. These are incremental encoders with two out-of-phase output channels. Each channel produces a series of equally  channel’s phase relationship determines the direction of motion. Quadrature encoders can detect both the direction and speed of rotation, making them ideal for applications where both parameters are required.  component in modern technology, playing a pivotal role in driving innovation across industries.


SEPTEMBER 2024 | ELECTRONICS FOR ENGINEERS 47


Photosensors are devices that detect and measure light. They play a crucial role in various applications, from industrial automation to consumer electronics.


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