Infrared remote control coding format and learning mode

1. Coding format
The existing infrared remote control includes two modes: PWM (pulse width modulation) and PPM (pulse position modulation).
The representatives of the two forms of coding are RC-5, RC-6 and the future RC-7 of NEC and PHILIPS respectively.
PWM (pulse width modulation): The duty cycle of the infrared carrier wave is used to represent "0" and "1". In order to save energy, in general, the time of transmitting the infrared carrier wave is fixed, and the duty cycle is changed by changing the time of not transmitting the carrier wave. For example, the commonly used TV remote control uses NEC UPD6121, and its "0" is 0.56ms for carrier wave transmission and 0.56ms for non-transmission; its "1" is 0.56ms for carrier wave transmission and 1.68ms for non-transmission; in addition, for the convenience of decoding, there is also a guide code, and the guide code of UPD6121 is 9ms for carrier wave transmission and 4.5ms for non-transmission. The total coding length of UPD6121 is 108ms.
But not all encoders are like this. For example, TOSHIBA's TC9012 has a pilot code of 4.5ms for carrier transmission and 4.5ms for non-transmission. Its "0" is 0.52ms for carrier transmission and 0.52ms for non-transmission, and its "1" is 0.52ms for carrier transmission and 1.04ms for non-transmission.
PPM (Pulse Position Modulation): "0" and "1" are represented by the position of the transmitted carrier. "0" is from transmitting the carrier to not transmitting the carrier, and "1" is from not transmitting the carrier to transmitting the carrier. The time for transmitting the carrier and not transmitting the carrier is the same, both 0.68ms, that is, the time for each bit is fixed.
Through the above analysis of the encoding, it can be concluded that it is very likely to fail to learn infrared with a certain fixed format of "0" and "1". That is, the 64-bit and 128-bit learning advertised on the market must be unreliable.
In addition, since the status of air conditioners is far more than that of televisions and audio and video, and there is no standard, each manufacturer makes one according to its own format, resulting in greater differences. For example: Midea's remote control uses PWM encoding, and the code length is about 120ms; Xinke's remote control also uses PWM encoding, and the code length is about 500ms. With such a big difference, if we talk about the concept of "bit", how many bits should it be? 64? 128? Obviously, it is impossible to contain such different lengths of codes.
2. Learning mode
The CPUs used to learn infrared now are nothing more than the following:
MCS-51 series, microchip pic16 series, winbond w741 series, holtek ht48 series The
above CPUs are widely used in remote controls due to their low prices and large usage.
The basic points of the above CPUs are: the execution speed is about 1us, and the data storage is generally 256 bytes. If you learn in a fixed format, you can generally learn 128 bits (other programs will occupy some data storage); if you do not follow a fixed format, you need to find the lowest common divisor of the code as the basic unit, then the number of bits that can be learned will be greatly reduced, and the practical effect cannot be achieved. However, even so, the lowest common denominator found cannot satisfy all infrared devices unless the minimum unit is 26us (1000000/38k). If this speed is reached, the speed of the above CPU is far from enough, and due to the increase in storage capacity, the data storage device is far from enough.
For TVs, audio, etc., dedicated remote control chips are generally used, such as NEC, Philips, Toshiba, Sanyo, Mitsubish, Panasonic chips, whose coding format is fixed, one key has only one code, and it is easier to learn. Air conditioners
are different. Each air conditioner manufacturer uses CPU to make remote control chips according to its own requirements, and there are many coding forms. For example, there may be no boot code (TV and audio have), the verification method takes the cumulative sum (TV and audio generally take the inverse code), etc. Because the air conditioner has many states, it must be sent all at once, including cooling, temperature, wind speed, automatic, timing, humidification, heating, etc., so the code is very long, and the same key sends different codes in different states, which makes it difficult to learn.