InfraRed(IR) Communication Prof Prabhat Ranjan DA-IICT, Gandhinagar
Reference http://www.jaec.info/home %20Automation/Communication-house/infraredcommunication.php
IR Standards The two most popular mediums in the wireless arena are Infrared (IR) and Radio Frequency (RF) IR technologies are better suited for short distance, low-to-medium data throughput, and wireless communication channels. Two common types of IR technologies: TV Remote (TVR) and IrDA (Infrared Data Association) standard protocol.
IrDA standard -> wireless communication link between two devices in which the information is transmitted using infrared light A set of specifications for providing a universal twoway wireless infrared data communications, based on a practical cost, short-range point-to-point user model The standard defines the physical characteristics of the interface, the communications protocols that provide for different needs, and the transmission speeds at which the infrared device communicates.
Two basics of the infrared communication standards are: IrDA-Data and IrDA-Control
IrDA-Data IrDA-Data defines the standard for the wireless, two-way infrared data transmission between two devices and consists of a set of mandatory protocols: IrPHY (Physical), IrLAP (Link Access), and IrLMP (Link Management)
IrDA-Control Infrared standard that allows wireless peripherals such as keyboards, mouse, game pads, joysticks, and other pointing devices to interact with many types of host devices Host devices include PCs, home appliances, game consoles, and TV/ audio devices/ Web set top boxes Not the same as the standard TV Remote Control. IrDA-Control has its own set of mandatory protocols: PHY (Physical), MAC (Media Access Control), and LLC (Logical Link Control).
IrDA technology has emerged as one of the most promising wireless solutions because it offers several compelling advantages over other types of wireless communication interfaces Although infrared is only applicable between two devices at a time and cannot transmit through walls, the positive aspects of this technology are many
Because infrared can only communicate from one device to another and because this communication must be line-of-sight, there is no risk that someone may intentionally or unintentionally obtain your information as it is being transferred IrDA infrared port module is the most mature of the wireless communications standards. These devices include cell phones, pagers, laptops, PDAs, digital cameras, handheld scanners, and laser printers.
The IrDA standard has both support and user applications in all major operating systems including all recent versions of Windows, Windows CE, Linux, as well as the Palm operating systems
IrDA protocol architecture
IrDA has defined an interface for infrared communications that consists of base three layers: IrPHY (Infrared Physical Layer), is implemented by hardware vendors and defines four types of infrared hardware implementation. IrLAP (Infrared Link Access Protocol) is a protocol, based on the HDLC, designed to control an infrared link IrLMP (Infrared Link Management Protocol) is a multiplexing protocol designed to run on top of IrLAP. IrLMP is multipoint-capable.
IrDA defined four kinds of infrared links to support different data rates. Included in these links are Serial Infrared (SIR) supporting speeds up to 115.2 Kbps, Medium Infrared (MIR) supporting 0.576 Mbps and 1.152 Mbps data rates, Fast Infrared (FIR) supporting a 4.0 Mbps data rate, and Very Fast Infrared (VFIR) supporting 14.0 Mbps.
In addition to the base standards, IrDA has specified several optional layers such as: Tiny TP (Tiny Transport Protocol) provide independently flow controlled transport connections segmentation and reassembly. IrCOMM determines how different devices can talk to each other via infrared. IrOBEX. (IrDA Object Exchange) is a communications protocol that facilitates the exchange of binary objects between devices LM-IAS (IrDA link management protocol information-access services) provides a set of services that allows stations to advertise information describing their capabilities to peer stations.
IR TV Control Format Data Formats for IR Remote Control Vishay Semiconductors
In most remote control transmission systems, only small data rates are required for transmitting the control functions of home entertainment equipment. The reliability of the transmission is essential as an incorrect interpretation of a transmitted code is not permissible. Corrupted signals must be ignored. In most coding schemes, commands are repeated until the remote controlled device reacts as desired
The operator can directly observe the result of pressing a key by means of visual feedback. Because IR signals are confined within a room and because there is only a short period of data transmission with each key press, there are no legal restrictions for IR transmission in the frequency band between 30 khz and 56 khz.
TSOP IR Receivers
As TSOP sense 36 KHz modulated light, it turns output low It will keep output low for some time and then again rise high. It not just sense 36 KHz but also determine if it continuous 36 KHz signal, or a burst of square waves. It rejects continuous 36 KHz like an ambient light.
Several methods of modulation have become well established. A reliable and power saving transmission method in which bursts of the carrier frequency are transmitted is called Pulse Code Modulation (PCM). There are three commonly used representations of one bit in remote control systems which are described in the following diagrams. The Bi Phase Coding has one rising or falling edge in the centre of each time slot (figure 1). In the Pulse Distance Coding, all bursts have the same length but the time between the bursts is different
In addition to different kinds of coding and different carrier frequencies, there are further variations in the data formats; with and without pre-burst, with different numbers of bits in a command, and with different bit lengths. Almost all codes have address bits and data bits. For reliability reasons, some codes send the data twice, once inverted and once non-inverted.
Usually the data command is repeatedly sent as long as the key is being pressed. There are different ways to distinguish between a multiple key press and an interruption of the transmission link (e.g. to avoid the TV selecting channel 11 when channel 1 was intended). Some codes use a toggle bit, which changes its value at each key-press
Some codes send a pre- or post-burst at the beginning and/or at the end of each key press. And some codes send the data only once for each key-press Two common data formats - the RC5 code and the NEC code
RC 5 coding The RC 5 standard uses a bi-phase coding the carrier frequency fixed at 36 khz The transmission of a data word begins with two start bits followed by a toggle bit The toggle bit changes its value at each new keypress The five address bits represent the address of the device to be controlled The six command bits contain the information to be transmitted
THE NEC CODE The NEC code uses bursts at a carrier frequency of 38 khz. The NEC code starts the transmission using a so called leader code, a burst with a length of 9 ms, followed by a pause of 4.5 ms and then the data word The original purpose of this leader code was to let the internal control loops in the receiver modules settle. But such a pre-burst is not necessary for the modern receivers to function correctly
THE NEC CODE... After transmitting the data word, only the leader code and a single bit are transmitted repeatedly for as long as a key is pressed A special property of this code is a constant word length in combination with pulse distance modulation Both the address and the data bits are transmitted twice, first as a normal byte followed by an inverted byte
THE NEC CODE The half period burst portion of each bit contains 22 pulses, each with a width of 8.77 μs and a period of 26.3 μs. A 0 is represented by a pulse distance of 1.125 ms and a 1 by a pulse distance of 2.25 ms. 8 address bits are used to identify the device to be controlled. A further 8 bits are used for the transmission of the command data
THE NEC CODE As mentioned above, the words are always followed, without a pause, by the inverted words. E.g., the transmission of the address word 00110111 and the command data word 000110 is performed by sending the bits: 00110111'11001000'00011010'11100101.
NEC Code