Consumer IR

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Consumer IR, or CIR, refers to a wide variety of devices employing the infrared electromagnetic spectrum for wireless communications. Most commonly found in television remote controls, infrared ports are equally ubiquitous in consumer electronics, such as PDAs, laptops, and computers. The functionality of CIR is as broad as the consumer electronics that carry it. For instance, a television remote control can convey a "channel up" command to the television, while a computer might be able to surf the internet solely via CIR. The type, speed, bandwidth, and power of the transmitted information depends on the particular CIR protocol employed.

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[edit] Protocol description

Since the Consumer IR protocols are for the most part not standardized, computers and universal remotes often memorize a bit stream, possibly with compression and possibly without determining the actual bit rate, and play it back. Similarities between remotes are often largely the accidental result of the finite selection of infrared encoder/decoder chips (though now microcontrollers are also used) and IR receiver modules or imitation of the older chips rather than by design. Manufacturers of consumer appliances often do reuse the same protocol on many similar devices, though for each manufacturer and device type there are usually multiple protocols in use; simply look at the code listings for any universal remote.

[edit] CIR and Protocol Implementation

With the ready availability of inexpensive microcontroller chips, many remotes may be based on such chips today rather than dedicated remote control encoder chips. This makes it easier to keep the same codes when moving the buttons on the remote.

Also, the decoder functionality will often be integrated into a more complicated micro-controller which controls the A/V device, eliminating the need for the separate chip. In the absence of a viable standard, the microcontrollers can be used to emulate the ambiguous protocols used by the old dedicated encoder/decoder chips and it appears that this is often the case. There are even stripped down 4 bit mask programmable microcontrollers designed only for remote control use (such as NEC uPD6124A (discontinued), uPD6125A (discontinued), uPD6126A (discontinued), uPD6132, uPD6133, uPD6134, µPD1724x, uPD67AMC, uPD68AMC, uPD68AMC, uPD6P9M1MC (OTP), upd6PLM3MC (OTP), and µPD17932x (8-bit)). These offer keyboard wake, low power standby modes, and sample controller code though similar features are present on more general PIC microcontrollers.

[edit] CIR-equipped Consumer Electronics

Sony manufactured a number of consumer devices of different types which shared a common protocol, called S-link. A jack on each device allowed the remote control signals to be interconnected between devices. The protocol included the useful but unusual feature of supporting more than one of the same type of device (such as multiple CD changers). Some A/V components could generate informational status codes that could be used to do things like automatically stop your tape deck when the CD you were recording stopped playing. Software running on a PC with a suitable interface could also control the A/V components and monitor their activity; for example, your computer could tell what disk and track were playing in your CD changer and look up the titles in one of the internet CD databases. Sony charges $5000 for access to the S-Link documentation[1].

Some infrared wireless PC keyboards and mice use protocols similar to Consumer IR devices. Some PC remote controls used for controlling computer media players, controlling presentation software, or other applications also use Consumer IR style protocols. Some computer remotes, keyboards, and mice may also use IrDA protocol though IrDA was designed for very short range use.

[edit] Standards

The RC5 and RECS 80 codes have been casually referred to as international standards [2][3]. Although it appears that they may just be the proprietary protocols developed by Philips and used in some of their ICs used by various manufacturers. Note that Philips Semiconductors is now NXP. RECS80 uses pulse position modulation and RC5 uses bi-phase. The Philips SAA3004, SAA3007, and SAA3008 encoders used RECS80, and the SAA3006 and SAA3010 encoder chips used RC5. The SAA3049A decoder chip decoded either type. All of these chips have been discontinued.

CEA-931-B defines a method for encapsulating remote control codes over IP and CEA-931-A defines a method for encapsulating remote control codes over IEEE-1394 [1]. These documents are not free even though free standards are the norm for Internet Protocols and contributed significantly to their widespread adoption.

[edit] Protocol limitations

The lack of standardization creates a lot of problems for consumers. The need to purchase universal remotes because the original can't control related functions on interconnected devices and upgrade them when you buy a new device, universal remotes that don't adequately control the devices, inability to control more than one of the same type unit, most consumer setups can't stop tape recording when CD ends, VCRs are often unable to control cable channels, etc. A well designed Consumer IR standard would have fields for device type (CD player, DVD player, TV, VCR, Cable Box, Receiver, Tape Deck, DVR, home automation, etc), unit number (settable via dip switches on remote and A/V component or other means), and function code and would standardize the values in each field. It would address the semantic differences between different similar operations (separate play and pause vs. play/pause, stop and eject vs stop/eject, etc) and would recommend that devices accept all of the semantic variations, not just the ones present on the original remote. This would allow consistent behavior across devices with a universal remote (or other control device) and would allow enhanced remotes with features like jog/shuttle. It would also allow devices to talk together, even across brands. Even if such a standard were created today, however, it would be years before consumers saw the full benefits due to legacy devices.

[edit] Technical information

  • Infrared Wavelength: around 930 nm, 870 nm and 950 nm.[4][5]
  • Carrier Frequency: Usually fixed carrier frequency, typically somewhere between 33 to 40 kHz or 50 to 60 kHz. Examination of LIRC datafiles shows the vast majority use 38 kHz. A few protocols such as ITT's protocol do not use a carrier frequency. Electronics component distributor Digi-Key carries Panasonic infrared receivers with 36.7, 38, 40, and 56.8 kHz carrier frequencies and Mouser carries Vishay receiver with carrier frequencies of 36, 38, 56, 455, and 33.0 to 57 kHz with maximum data rates of 800 and 4000 bit/s (20k for the 455 kHz carrier).
  • Modulation Schemes: typically 100% amplitude-shift keying (ASK). May also involve pulse-position modulation, biphase/manchester encoding, etc. of the transmitted pulses (as opposed to the carrier itself). Most remotes use the length of the space between pulses to encode data.
  • Data Rate: usually significantly lower than the carrier frequency. Most protocols seem to range between 120 Hz and 4 kHz. Data rate may be variable as some common bit encoding schemes vary the timing between pulses to distinguish between a 1 and 0.
  • Encoding: varies based on encoder/decoder chips used. Usually includes some redundancy for error detection or correction. For example, some NEC chips send the same code four times (inverted the second and forth time).
  • Key to code mapping: varies from remote control to remote control. In many cases, the codes sent may have more to do with the row and column positions on the remote than any unified plan.
  • An analysis of remote control definition files from the LIRC project yielded the following statistics on carrier frequency:
    • 111 38000 Hz
    • 81 56000 Hz
    • 41 40000 Hz
    • 32 36000 Hz
    • 13 39200 Hz
    • 8 32000 Hz
    • 3 40244 Hz
    • 3 37037 Hz
    • 2 37916 Hz
    • 1 57600 Hz
    • 1 56800 Hz
    • 1 44000 Hz
    • 1 42000 Hz
    • 1 38380 Hz
    • 1 14000 Hz
      Note that the default frequency is 38000 Hz and frequency was not specified on about 90% of the remotes so it appears that the overwhelming majority use 38 kHz. Considerable additional statistical information could be gleaned from elaborate parsing of the LIRC files.

[edit] External links

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[edit] See also

IrDA

[edit] Notes

  1. ^ Sony S-Link Resource Center
  2. ^ Juergen Putzger. Decoding IR Remote controls
  3. ^ Eric Maass (2001). 'How does a universal remote control work?', MadSci
  4. ^ Lamp Section, National Electrical Manufacturers Association (1998). Interaction of Infrared Controls And Electronic Compact Fluorescent Lamps
  5. ^ ePanorama. Infrared remote control technology