Optoelectronics are components that use light to control or adjust a signal and create resistance. Without optoelectronics, there would be no current and modern state of the art that we know today and DVD technology. never would have been, and high-speed isolation between the circuits would be a challenge


The LDR (light-dependent resistor) is one of the simplest optoelectronic components. Their resistance depends on the amount of light the sensor detects, and they usually have two leads from the component.

LDRs generally come in two flavours, through-hole and surface mount, but they are not used regularly in modern designs. LDRs are often cheaply available in the market but have the disadvantage of not being RoHS compliant as they contain the chemical cadmium, which is considered a hazard to those who handle it directly.


Photodiodes are similar to LDRs but are more diodes than resistors. Photodiodes are only used in reverse voltage configurations. When the light of a certain frequency (depending on the photodiode) hits the sensor, it causes the diode to conduct briefly. in a brief current flow and in response to this a change in voltage

They also come in different flavors and can be found on different devices. Remote TVs are one of the most popular devices that use photodiodes. Remote controls contain an IR LED that emits digital IR signals that are detected by the TV using an IR photodiode.

Photodiodes come in a variety of package configurations, but almost always have two connections and are categorized by D or PD. IR photodiodes are easy to identify completely black packaging, while photodiodes for visible light contain transparent windows in their packaging


An optoisolator is a component that consists of a photodiode and an LED in one housing. The LED is mounted so that it faces the photodiode directly and serves as an input for the optoisolator and the photodiode as an output. , the photodiode becomes conductive.

An Optoisolator Some optoisolators are completely sealed with all parts are hidden, while others expose them to prevent the LED light from reaching the optoisolator. Opto Isolators are used to electrically isolate two circuits, which is why they are often used in circuits to protect against high voltage. Connection of circuits to low-voltage circuits.

Optoisolators are available in SMD and through-hole packages, but through-hole packages are arguably the most common variety. Optoisolators often have four legs but sometimes can have six and are mostly found in DIP packages – they are considered integrated circuits and are therefore labeled with IC or U marked


The light-emitting diode (LED) is a semiconductor device that emits light when an electrical current flows through it. Light is created when particles through which current flows (known as electrons and holes) combine in the semiconductor material.

LEDs are available in SMD and through-hole packages but the most common are 3mm, 5mm, 5050 SMD, 2835 SMD, 3030 SMD, 3528 SMD, and 5060

Laser Diode

Laser diodes are very similar to LEDs and in some cases, they can be confused with LEDs. However, laser diodes are often found in larger cylindrical metal housings. While you will find laser diodes in SMD packages, because of their size and power requirements, they are much more commonly found in through-hole packages.

A common place to find laser diodes is in CD and DVD players, which use lasers to read and write to discs. Laser diodes, known as LEDs or simply D, can have large solid metal plates to help dissipate excess heat and often have three legs to ensure that they are properly inserted.