Infrared technology is a wireless data transmission protocol used to control and operate many devices. However, infrared-enabled devices, such as mobile phones or laptops, cannot exchange data if there is any obstacle in between. In contrast to radio frequency protocol, infrared technologies are better suited for short-range communication channels. Infrared protocol is based on light emitting diode that produces red light invisible to human eye. Because infrared communication requires line-of-sight, the risk that someone intentionally may obtain the transmitted information is decreased.
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RC5 infrared code is commonly used protocol for data communication. RC5 has 32 different addresses with 64 instructions on each address for a total of 2,048 different instructions. Every device uses its own address which enables controlling more devices with one remote control, for example you can change the volume of the TV without changing the volume of your Hi-Fi. The infrared code, sent to the receiver, consists of 14 bits.
ITT infrared protocol does not use a modulated carrier frequency to transmit commands. This protocol is an older protocol that sends messages with 14 pulses. The advantage of the protocol is its reliability and the fact it consumes little energy. However, ITT can trigger false commands. The infrared code has 4 bit address and command length of 6 bits.
Infrared Data Association is the most widespread infrared protocol. It is built in mobile phones, laptops, printers and personal digital assistants. IrDA consists of three mandatory protocols: IrPHY (Physical). IrLAP (Link Access) and IrLMP (Link Management). There are four types of infrared links to support different speeds of data transmission: Serial Infrared supports transmission up to 115.2 Kbps, Medium Infrared supports 0.576 Mbps, Fast Infrared supports 4.0 Mbps and Very Fast Infrared sends data at up to 14.0 Mbps speed.
NEC and SIRC
The NEC protocol uses carrier frequency at 38 kHz and pulse distance encoding. Known as Japanese format, the protocol uses 8 bit address with 8 bit commands with bit time of 1.12 or 2.25 ms. Developed by Sony, SIRC protocol comes in three versions: 12 bit, 15 bit and 20 bit. The 20-bit version is the only SIRC that uses 8-bit extended word. SIRC is most commonly used for entertainment devices, such as TV, DVD players and Hi-Fi.
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