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1. The coded signal sent by the remote control drives the infrared emitting tube, which must emit infrared light with a wavelength range of about 940nm, 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 list, it is obviously not possible To achieve the purpose of control. However, almost all infrared home appliance remote controls follow this standard. Because of this physical foundation, the all-in-one remote control is possible.

2. The remote control sends out a string of coded signals that only lasts for tens of milliseconds, most of which are more than ten milliseconds or more than one hundred milliseconds to repeat once. A string of codes includes about ten to ten binary codes. The duration or bit length of each binary code is only about 2ms, and the frequency is only on the order of 500kz. To transmit longer distances, the carrier must be used to modulate these signals to tens of khz, and the most used is 38khz. The carrier frequency of most ordinary remote controllers is 1/12 of the oscillation frequency of the ceramic oscillator used. The most commonly used ceramic oscillator is 455khz, so the most commonly used carrier is 455khz/12=37.9khz, or 38k carrier for short. In addition, there are 480khz (40k), 440khz (37k), 432khz (36k) and other specifications, and there are also about 200k carrier waves for high-speed encoding. The infrared receiver is an integrated component. In order to receive the required codes more targeted, it is designed as a band-pass filter with the carrier as the center frequency and only allows the signal of the specified carrier to pass. Obviously this is the second physical condition that the all-in-one remote control should meet. However, household appliances mostly use 38k, and many infrared receivers can also receive 40k or 36k remote control codes with similar frequencies.

3. A device is controlled. In addition to satisfying the two basic physical conditions mentioned above, the most important change is of course that the remote control sends out a series of binary coded signals. This is also the case that different remote controls cannot be mutually compatible. The main reason. As hundreds of encoding methods coexist in the market, there is no unified international standard, only the de facto standard of each chip manufacturer. This is also the biggest difficulty in simulating and replacing various original remote controls. With the continuous development of technology, many companies do not use universal coding chips when developing remote control subsystems for home appliances. Instead, they use universal single-chip microcomputers to compile some codes at will. This makes the problem of universal remote control more complicated.

4. Using the same encoding chip does not mean that it can be used universally, because there is also a customer code. The original intention of the client code design is to distinguish between different devices without interfering with each other. Initially, chip manufacturers will arrange different customer codes for different home appliance manufacturers from a global perspective to regulate the market. For example, video recorders and televisions use different device codes. The device codes assigned to factory A and the device codes assigned to factory B are differentiated in Different ranges.

5. Using the same coding chip and the same customer code does not mean that it must be universal, because there is still no fixed pattern to follow in the distribution and use of command codes. The remote control coding chip simply supports dozens of There are thousands of different command codes, but the remote control often only has dozens of keys, or even a few keys. How to select these dozens of keys from them, and how these keys are allocated and used, different system designers have their own ideas. In this way, things are more complicated.