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Infrared: Before understanding infrared receiving LEDs, let's first understand what "infrared" is. Infrared is actually the abbreviation for infrared, which is a type of light in the spectrum (electromagnetic wave) that is invisible to the naked eye between 0.75 and 1000 microns.

Infrared receiving LED is a device used to receive infrared radiation. Infrared receiving head, abbreviated as receiving head, can also be called infrared receiver, infrared receiving tube, infrared receiving module, remote control receiving head, or adding a "line" after infrared, such as infrared receiving LED. The English name of the infrared receiver head is Infrared Receiver Module, abbreviated as IRM.

Appearance: According to appearance, it can be divided into two types: nose bridge type and ball type (dot type). In the nose bridge type, it can be subdivided into large nose bridges, standard nose bridges, and small nose bridges. In addition, there are other special types, such as ultra-thin, mini, straw hat, patch, and wire receiving heads.

Classification: In addition to classifying by appearance, it can also be classified by packaging method, which is more accurate. At present, the connectors available in the market can be divided into two main categories in terms of packaging methods: pressure models and glue injection types. Generally speaking, the nasal bridge type belongs to the glue filled type, while the spherical type belongs to the compression model. In terms of the two packaging processes, the investment in molding equipment is relatively high, and the price of the adhesive cake used is relatively high, so the overall price is higher. Of course, its ability to resist light interference is strong, and the acceptance angle is large (circular 360 degree acceptance); The investment in glue injection equipment is small, and most of the products produced by domestic factories in the past are glue injection products. The advantage is low price, but the disadvantage is poor resistance to light interference, and the acceptance angle is small (270 degrees acceptance). Of course, there is also a pseudo compression model, which uses the glue injection method to create a spherical shape, similar to the shape produced by compression molding, but its performance is definitely not as good as that of compression molding. Sometimes, there is an iron vest on the outside of the connector, so the connector can be divided into two types: red plastic sealing and iron shell. The advantage of multiple iron shells is that they have an additional layer of external shielding, which has a certain shielding effect on light and power interference, and the acceptance performance is relatively stable. Of course, assuming the product design is OK, the acceptance distance for using plastic packaging under the same conditions is slightly longer. Of course, there may be some price differences in whether to wear an iron shell or not, so when choosing a connector, it is important to carefully determine whether to wear an iron shell based on the design. Under normal circumstances, plastic packaging is commonly used on toy products, while those with iron shells are more commonly used on household appliances.

Composition: The receiver head is mainly composed of four major parts: photodiodes (PDs), chips (ICs), brackets, and colloids (pigments, epoxy resins), which are combined and packaged together.

The main function of PD is to receive optical signals. There are different sizes: large, medium, and small. The larger the size, the farther the acceptance distance and the larger the acceptance angle when other raw materials are the same.

IC is a processing component for LED infrared connectors, mainly composed of silicon crystals and circuits. It is a highly integrated device with main functions such as filtering, shaping, decoding, and amplification. The main raw material for determining the performance of the connector is related to various factors such as product's ability to resist light interference, power interference, acceptance distance, decoding ability, and product stability.

The bracket is the pin part of the receiving head, which connects the IC functional pins externally and fixes the chip.

Colloid is a black substance composed of a mixture of pigments and epoxy resin, where epoxy resin plays a role in containing PD and IC. Pigments have a significant impact on the product's ability to resist light interference. Good pigments such as Japan's 2245 are more expensive, but have better light filtering performance, which can filter visible light below 850nm. Another type of packaging used in the mold is adhesive cake, which has the best ability to resist light interference.

So from the perspective of appearance, if the connectors look the same, the prices of products with the same appearance on the market vary from 0.4 to 1 yuan due to the different components. Due to the fact that IC is the biggest factor affecting price, it is important to pay attention to cost-effectiveness when selecting products, and not just focus on price and forget about quality.

Working principle of infrared receiving LED: Infrared receiving LED can generally accept infrared light in the 850-1100nm wavelength range, with the main focus being on receiving 940nm (therefore, it is best to choose a 940nm transmitting tube when matching with an infrared transmitting tube). PD converts the optical signal emitted by the infrared emission tube into a small electrical signal. This signal is amplified by an internal amplifier in the IC, and then restored to the original code emitted by the remote control after automatic gain control, bandpass filtering, demodulation, and waveform shaping. It is input to the coding recognition circuit on the electrical appliance through the signal output pin of the receiver head.