Principle of infrared remote control

Many electrical appliances use infrared remote control, so what is the working principle of infrared remote control? First, let's take a look at what infrared is.
The visible light that can be seen by the human eye is arranged in order of wavelength from long to short, and the order is red, orange, yellow, green, cyan, blue, and violet. The wave of red light
The long range of the remote control is 0.62~0.76μm; the wavelength range of the violet light is 0.38~0.46μm. Light with a wavelength shorter than violet is called ultraviolet light, and light with a wavelength longer than red light is called infrared light.
Infrared remote control is to use the near-infrared wavelength between 0.76 ~ 1.5μm to transmit control signals.
The commonly used infrared remote control system is generally divided into two parts: transmitting and receiving.
The main components of the emitting part are infrared light-emitting diodes. It is actually a special light-emitting diode. Because its internal material is different from ordinary light-emitting diodes, when a certain voltage is applied to its two ends, it emits infrared light instead of visible light.
The wavelength of infrared light emitted by a large number of infrared light-emitting diodes is about 940nm, and the shape is the same as that of ordinary light-emitting diodes, but the color is different.
Infrared light-emitting diodes generally have three colors: black, dark blue, and transparent.
The method of judging the quality of infrared light-emitting diodes is the same as that of ordinary diodes: use a multimeter to measure the forward and reverse resistance of infrared light-emitting diodes.
The luminous efficiency of infrared light-emitting diodes can only be accurately measured by special instruments, and can only be roughly determined by the pull distance method under amateur conditions. The infrared receiving tube of the receiving part is a photodiode.
In practical applications, it is necessary to add reverse bias to the infrared receiving diode, so that it can work normally, that is, when the infrared receiving diode is used in the circuit, it is used in the reverse direction, so that higher sensitivity can be obtained.
Infrared receiving diodes generally have two types: round and square.
Since the transmission power of infrared light-emitting diodes is generally small (about 15mW), the signal received by the infrared receiving diode is relatively weak, so a high-gain amplifier circuit should be added.
In the past few years, special amplifier circuits for infrared reception such as PC1373H and CX20106A were commonly used. In recent years, whether it is amateur production or formal products, most of them use finished infrared receivers.
There are roughly two types of packages for the finished infrared receiver: one is shielded with iron sheets; the other is plastic package. There are three pins, namely power positive (VDD), power negative (GND) and data output (VO or OUT). The pin arrangement of the infrared receiver is different due to different models, please refer to the manufacturer's instructions for use. The advantage of the finished infrared receiver is that it does not require complicated debugging and shielding of the shell, and it is very convenient to use like a triode. But pay attention to the carrier frequency of the finished infrared receiver when using it.
The commonly used carrier frequency of infrared remote control is 38kHz, which is determined by the 455kHz ceramic oscillator used at the transmitter.
At the transmitting end, the crystal oscillator needs to be divided by integer, and the frequency division coefficient is generally 12, so 455kHz÷12≈37.9kHz≈38kHz. There are also some remote control systems that use 36kHz, 40kHz, 56kHz, etc., which are generally determined by the oscillation frequency of the crystal oscillator at the transmitting end.
The characteristic of infrared remote control is that it does not affect the surrounding environment and does not interfere with other electrical equipment. Because it cannot penetrate the wall, household appliances in different rooms can use a universal remote control without mutual interference; circuit debugging is simple, as long as the given circuit is connected correctly, generally it can be put into work without any debugging; codec Easy, multi-channel remote control is possible.
Since various manufacturers have produced a large number of special integrated circuits for infrared remote control, you can follow the picture and ask for it when needed. Therefore, infrared remote control has been widely used in household appliances and indoor short-range (less than 10 meters) remote control.
Infrared remote control system of multi-channel control The infrared transmitting part of multi-channel control generally has many buttons, which represent different control functions. When the transmitter presses a certain button, there are correspondingly different output states at the receiver.
The output state of the receiving end can be roughly divided into five forms: pulse, level, self-locking, interlocking, and data. The "pulse" output is that when the button of the transmitter is pressed, the corresponding output of the receiver outputs a "valid pulse", and the width is generally about 100ms. "Level" output means that when the transmitter presses the button, the receiver outputs the "effective level" corresponding to the output, and when the transmitter releases the button, the receiver "effective level" disappears. The "valid pulse" and "valid level" here may be high or low, depending on the static state of the corresponding output pin, such as low when static, "high" is valid. ; If it is high in static state, "low" is valid. In most cases "high" is valid. The "self-locking" output means that every time the transmitter presses a certain key, the corresponding output end of the receiver changes the state once, that is, the original high level changes to a low level, and the original low level changes to a high level. This output is suitable for use as a power switch, mute control, etc. This form of output is sometimes called "inverted". "Interlock" output means that multiple outputs are cleared from each other, and only one output is valid at the same time. This is the case for the selection of TV stations, and others such as dimming, speed regulation, and audio input selection.
"Data" output refers to coding some transmitting keys with numbers, and using several outputs of the receiving end to form a binary number to represent different key inputs.
In general, in addition to several bits of data output, the receiver should also have a "data valid" output, so that the later stage can get the data in a timely manner. This output form is generally used to interface with a microcontroller or a microcomputer. In addition to the above output forms, there are two forms of "latching" and "temporary storage". The so-called "latch" output refers to the signal sent by the transmitter each time, and the corresponding output of the receiver is "stored" until a new signal is received; the "temporary storage" output is the same as the above-mentioned " ;Level" output is similar.