IR Remote Control Codes for Audio/Video Equipments

With most pieces of consumer electronics, from camcorders to stereo equipment, an infrared remote control is usually always included.Video and audio apparatus, computers and also lighting installationsnowadays often operate on infra-red remote control.The carrier frequencyof such infra-red signals is typically in the order of around 36 kHz. The control codes are sent in serial format modulated to that36 kHz carrier frequecy (usally by turning the carrier on and off).There are many different coding systems in use, and generallydifferent manufacturers use different codes and different datarates for transmission."IR" stands for infrared. Infrared light is invisible since its frequency is below that of visible red. Otherwise, it is like any other light source, operating under the same laws of physics. In most cases, the IR signals are produced by an LED source. TV remotes send commands only one way, in a low-speed burst for distances of up to 30 feet. They use directed IR with LEDs that have a moderate cone angle to improve ease-of-use characteristics. The IR signal sent out by those devices is generally modulated to around38 kHz carrier using amplitude shift keying (carrier on or off). The data rate send is generally in ra range of 100-2000 bps. Please note that there are some IR systems which use other frequencies and other modulation systems.IR transmit and receive systems are inexpensive and are generally reliable.

Overview of most common coding schemes: p8v12ve
Almost all infrared remote controls use the same modulation scheme. The transmitter sends a 38kHz to 40KHz square wave (optimized to 50% duty cycle) signal gated by a stream of bits. This signal is sent to one or several infrared LEDs for transmission. The wavelength for infrared light used in most commercial applications is 940nm +/- 100nm. Transmitter circuits are discussed below
The receiver circuit consists of a photodiode (sensitive to the same wavelength mentioned above), a pre-amplifier and a demodulator circuit. The preamplifier circuit has a band-pass filter typically with a 3dB drop off at +/- 3kHz from the center frequency. The receiver circuit also has an adjustable gain control (AGC) which modifies the level of the incoming signal for the demodulator circuit. Since this gain adjustment is necessary in most circuits for proper demodulation almost all code protocols have a long leading pulse which sets the AGC accordingly. The output of the receiver is a bit stream which corresponds to the original signal used to gate the modulator. It is important to note that almost all protocols are active low (i.e. in terms of the carrier signal a low voltage, typically 0V, corresponds to a logical '1' and a high voltage, typically 5V, corresponds to a logical '0'). Receiver circuits and modules are discussed below.
There are two coding standards that are the most commonly used in consumer A/V products. These are the RC-5 and RECS-80 standards. They are explained below.

RECS-80:
The RECS-80 code uses pulse-length modulation. Each bit that is transmitted has the following coding scheme:
· Logical '0's are represented by a high level of the duration 'T' followed by a low level of duration '2T'.
· Logical '1's are represented by a high level of duration 'T' followed by a low level of duration '3T'.
The duration of 'T' may vary depending on the manufacturer but is typically 550ns. An example of RECS-80 coding is shown below.


Note how the transmission of a logical '1' takes more time than a logical '0'.
RC-5:
This coding protocol contrasts the RECS-80 protocol by using a uniform duration of all bits. A transition, from high to low or low to high, in the middle of the time interval encodes the logical value.
· A Logical '0' is encoded by a high to low transition
· A Logical '1' is encoded by a low to high transition.
Thus additional transitions at the beginning of each bit are necessary to set the proper start level if a series of equal bits is sent. This additional transition is not need if the next bit has a different value. This coding technique is commonly referred to as 'biphase' code. An example of this coding sequence is shown below.

Daewoo infrared remote protocol

By the Daewoo protocol a logical 0 bit exists of a high puls with a duration time of 550 µs followed by a low puls of 450 µs this means that the total duration time of a logical zero bit is 1ms. A logical 1 bit is formed by a high on time of 550 µs followed by low signal of 1450 µs this means also that the total duration time of a logical one bit is 2 ms. The carrier frequency of the infrared signal is 38 kHz. When you will decode the signal with an integrated receiver module you need a receiver module wich is tuned on 38 kHz like the TSOP1838 fabricated by Vishay. It will function also with a 36 kHz module but the sensitivity is less than by a 38 kHz module. Because the receiver (mostly in hobby applications a microprocessor) needs to trigger on a new received code the protocol starts with a start bit of 8ms high level pulse and a 4 ms low level pulse. After this the 7 address bits and 7 command bits are sent. But the two words are divided by a 550µs high level signal and 4ms low level signal. Terminating the protocol is done with an another high level signal of 550µs. The time between two startbits of bitstreams when the button on the remote control is being pressed =60 ms.

SONY infrared remote protocol

The Sony remote control is based on the Pulse-Width signal coding scheme. The code exists of 12 bits sent on a 40kHz carrier wave. The code starts with a header of 2,4ms or 4 times T where T is 600µS. The header is followed by 7 command bits and 5 adres bits. The address and commands exists of logical ones and zeros. A logical one is formed by a space of 600µS or 1T and a pulse of 1200 µS or 2T. A logical zero is formed by a space of 600 µS and pulse of 600µS. The space between 2 transmitted codes when a button is being pressed is 40mS. The bits are transmitted least significant bits first. The total length of a bitstream is always 45ms.

Panasonic's old infrared remote protocol

The protocol is similar with the RECS-80 protocol but it use more bits than the RECS-80 protocol. For the datatransmission Panasonic uses the pulse-place modulation. For the communication a pulse is used with a fixed length, followed by a pause wich represents The logical state of the bit. 2048 codes are defined in this protocol, divided in 5 bits of custom code and 6 bits of data code. The custom code is a value wich represents the manufacturer code and the data code is a value wich represents the pressed button on the remote control. The full transmitted code is 22 bits: First a header is sent then the custom code (5 bits), then the data code, followed by the inverse of the custom code and the invers of the data code, And to terminate a stopbit is added to the code. The invers transmitted bits are very usefull for the error detection. Each first part of a bit is always a high level with a fixed time and is followed by a low level where the time defines if the bit is a logic 1 or a logic 0.
Timing diagram:
T =420 µs to approx 424 µs in the USA and Canada
T=454 µs to approx 460 µs in Europe and others
The header is 8T high and 8T low
A 1 is coded 2T high and 6T low
A 0 is coded 2T high and 2T low
Panasonic IR remote control v