1. The coded signal from the remote control drives the infrared emission tube. It must emit infrared light with a wavelength range of about 940 nm. Because the receiving diode of the infrared receiver is mainly sensitive to this part of the infrared light signal, if the wavelength range is not in this column, it is obviously impossible. To achieve the purpose of control. However, almost all infrared appliance remote controls follow this standard. Because of this physical foundation, the all-in-one remote control is possible.
2. The remote controller sends a series of encoded signals for only a few tens of ms, most of which are repeated for more than ten ms or more than one hundred ms. A series of codes also includes about ten to dozens of binary codes, in other words, The duration of each binary code or the bit length is only about 2ms, and the frequency is only 500kz. To transmit a farther distance, it is necessary to pass the carrier to tens of khz. The most used is 38khz. The carrier frequency of most common remote controllers is 1/12 of the oscillation frequency of the ceramic oscillator used. The most commonly used ceramic oscillator is the 455khz specification, so the most commonly used carrier is 455khz/12=37.9khz, referred to as 38k carrier. In addition, there are 480khz (40k), 440khz (37k), 432khz (36k) and other specifications, there are also about 200k carrier for high-speed encoding. The infrared receiver is an integrated component. In order to receive the required code more specifically, it is designed as a band-pass filter with a carrier-centered frequency, and only allows signals of a specified carrier to pass. Obviously this is the second physical condition that the all-in-one remote control should satisfy. However, household appliances use 38k, and many infrared receivers can also receive remote control codes with similar frequencies of 40k or 36k.
3. A device is controlled. In addition to satisfying the two basic physical conditions mentioned above, the most important changes are of course the remote controller sends out a series of binary coded signals, which is also different from the remote controller. The main reason. Since there are hundreds of thousands of encoding methods coexisting in the market, there is no unified international standard, only the de facto standard of each chip manufacturer, which is the biggest difficulty in simulating and replacing various original remote controllers. With the continuous development of technology, many companies have not used general-purpose coding chips when developing remote control subsystems for household electrical appliances. Instead, they use proprietary microcontrollers to customize some codes at will, which complicates the problem of universal remote control.
4. Using the same encoding chip does not mean that it can be used universally because there are customer codes. The original intention of the customer code design is that different devices can be distinguished from each other without interference. Initially, chip manufacturers will arrange different customer codes for different home appliance manufacturers to regulate the market. For example, video recorders and TV sets use different device codes. The device code assigned to plant A and the device code assigned by plant B are differentiated. Within a different range.
5. Using the same encoding chip and the same client code can not mean that it can be universal, because there is still no fixed mode to follow the allocation and use of the command code. The remote control coding chip simply supports dozens of There are thousands of command codes, but the remote control often only has dozens of keys, even only a few keys. How to choose these dozens of keys, how to assign these keys, different system designers do their own Set, so things are more complicated.
