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This article explains the various principles and applications of infrared remote control

Infrared remote control is a wireless, non-contact control technology, with strong anti-interference ability, reliable information transmission, low power consumption, low cost, easy implementation, etc. It is widely used by many Electronic devices, especially household appliances, and is becoming more and more It is widely used in computer and mobile phone systems. This paper firstly introduces the basic principle of the infrared remote control module, and then explains the working principle of the infrared remote control module in detail, and finally introduces the important links and applications of the infrared remote control.

Infrared remote control is a wireless, non-contact control technology, with strong anti-interference ability, reliable information transmission, low power consumption, low cost, easy implementation, etc. It is widely used by many electronic devices, especially household appliances, and is becoming more and more It is widely used in computer and mobile phone systems. This paper firstly introduces the basic principle of the infrared remote control module, and then explains the working principle of the infrared remote control module in detail, and finally introduces the important links and applications of the infrared remote control.

The basic principle of infrared remote control

The transmitting circuit of the infrared remote control uses infrared light-emitting diodes to emit modulated infrared light waves; the infrared receiving circuit is composed of infrared receiving diodes, triodes or silicon photocells, which convert the infrared light emitted by the infrared transmitter into corresponding electrical signals, and then send them back. set the amplifier.

The transmitter is generally composed of command keys (or joysticks), command coding system, modulation circuit, drive circuit, transmitting circuit and other parts. When the command key is pressed or the operating lever is pushed, the command coding circuit generates the required command coding signal, the command coding signal modulates the carrier wave, and then the power is amplified by the driving circuit, and then the transmitting circuit transmits the modulated command code to the outside. Signal.

The receiving circuit is generally composed of a receiving circuit, an amplifying circuit, a modulation circuit, an instruction decoding circuit, a driving circuit, and an executive circuit (mechanism). The receiving circuit receives the modulated coded command signal sent by the transmitter, amplifies it and then sends it to the demodulation circuit, and the demodulation circuit demodulates the modulated command coded signal, that is, restores it to a coded signal. The instruction decoder decodes the encoded instruction signal, and finally the drive circuit drives the execution circuit to realize the operation control (mechanism) of various instructions.
 
The working principle of infrared remote control module

Press a certain key of the remote control, the remote control will send out a series of modulated signals. After the signal is received by the infrared integrated module, it will output the demodulated digital pulse. Each key corresponds to a different pulse, so it can identify different pulses. pulses to identify different keys.

This article explains the various principles and applications of infrared remote control

The picture above is a very common car MP3 remote control, which is relatively small and easy to use. The following is the principle of infrared emission and reception:

This article explains the various principles and applications of infrared remote control
  
  

At this point, readers may have doubts, so the pulse rules produced by different modulation and demodulation methods are different? Yes, it does.

There are many dedicated chips for remote control transmitters, which can be divided into two categories according to the encoding format. Here we will explain the one that is more widely used and easier to decode. Now we take the uPD6121G of Japan’s NEC to form a transmitting circuit as an example to illustrate the encoding principle (general family DVDs, VCDs, and audios all use this encoding). When the transmitter button is pressed, a remote control code will be sent out, and the remote control code will be different for different keys. This remote control code has the following characteristics:

Using the serial code of pulse width modulation, the combination of pulse width of 0.565ms, interval of 0.56ms and period of 1.125ms represents binary “0”; the combination of pulse width of 0.565ms, interval of 1.685ms and period of 2.25ms Represents a binary “1”, and its waveform is shown in the figure.
   

This article explains the various principles and applications of infrared remote control

As shown in the figure, the low-level duration of the front end of 0 and 1 is 0.56ms, then the high-level duration of the following is different, 0 is 0.56ms, 1 is 1.685ms, if you find the difference, you will recognize it during programming Based on it!

The 32-bit binary code composed of the above “0” and “1” is subjected to secondary modulation by the carrier frequency of 38kHz to improve the transmission efficiency and achieve the purpose of reducing power consumption. And then through the infrared emitting diode to generate infrared radiation to the space, as shown in the figure.
  
  

This article explains the various principles and applications of infrared remote control

The remote control code generated by UPD6121G is a continuous 32-bit binary code group, of which the first 16 digits are the user identification code, which can distinguish different electrical equipment and prevent the remote control codes of different models from interfering with each other. The user identification code of the chip is fixed as hexadecimal 01H; the last 16 bits are 8-bit operation code (function code) and its inverse code. The UPD6121G supports up to 128 different combinations of codes.

Please see the picture below, from the Internet:
  
  

This article explains the various principles and applications of infrared remote control

When a key is pressed for more than 36ms, the oscillator activates the chip, and will transmit a set of 108ms encoded pulses. The 108ms transmit code consists of a pilot code (9ms), a result code (4.5ms), and a lower 8-bit address code (9ms). ~18ms), high 8-bit address code (9ms~18ms), 8-bit data code (9ms~18ms) and the inverse code (9ms~18ms) of these 8-bit data. If the key is pressed for more than 108ms and still not released, the code to be transmitted next (burst code) will only consist of the start code (9ms) and the end code (2.25ms). (Actually, the action of the human hand is very slow. Even if you press the button quickly, it may still exceed 108ms for the chip, so how to deal with the burst code is very critical)

After the button is pressed, the remote control periodically sends out the same 32-bit binary code with a period of about 108ms. The duration of a group of codes itself varies with the number of binary “0” and “1” it contains, about 45-63ms. The picture shows the transmission waveform.

This article explains the various principles and applications of infrared remote control

  
  
An important part of infrared remote control

The infrared remote control device includes two parts: infrared emission (ie remote control) and infrared reception. Since almost all objects are constantly emitting infrared rays, how can we ensure that the control signal emitted by the designated remote control can be accurately received by the receiving device without being interfered by other signals? control in four aspects.

1. The matching use of the infrared sensor The infrared emission sensor and the infrared receiving sensor are used together to form an infrared remote control system.

The infrared emission sensor for remote control, that is, infrared light emitting diode, is made of semiconductor materials such as gallium arsenide or gallium arsenide aluminum arsenide. The luminous efficiency of the former is lower than that of the latter. The peak wavelength is the emission wavelength corresponding to the maximum infrared light intensity emitted by the infrared light-emitting diode, and the peak wavelength of the infrared light-emitting diode is usually 0.88μm~O.951Am. There are two types of infrared receiving sensors for remote control: photodiode and phototransistor. The response wavelength (also called peak wavelength) reflects the spectral response characteristics of photodiode and phototransistor. It can be seen that it is very important that the peak wavelength of the infrared light-emitting diode used in the remote control system and the response wavelength of the infrared receiving sensor must be consistent or similar to improve the receiving efficiency.

2. Signal modulation and demodulation The infrared remote control signal is a series of binary pulse codes. In order to prevent it from being interfered by other infrared signals during wireless transmission, it is usually modulated on a specific carrier frequency first, and then emitted by infrared light-emitting diodes. The infrared receiving device will filter out other clutter only. The signal of this specific frequency is received and restored to a binary pulse code, that is, demodulation. The figure below is a schematic diagram of infrared emission and reception. In Fig. 1, the state in which no signal is sent is called the null or 0 state, and the state in which the signal is sent out in pulses at a certain frequency is called the mark or 1 state. In the infrared remote control system of consumer electronic products, the carrier frequency of the infrared signal is usually 30kHz-OkHz, and the standard frequencies are 30kHz, 33kHz, 36KHz, 36.7kHz, 38kHz, 40kHz and 56kHz. Other frequencies in this range can also be identified.

3. Encoding and decoding

Since the infrared remote control signal is a series of binary pulse codes, what kind of combination of space and mark is used to represent the “0” and “1” of binary numbers, that is, the coding method used for signal transmission, which is also the infrared remote control signal. The sender and receiver need to be agreed in advance. Generally, there are three encoding methods used in infrared remote control systems:
  

1) FSK (frequency shift keying) method
  

The frequency shift keying method uses two different pulse frequencies to represent “0” and “1′ of binary numbers, respectively. The following figure is a schematic diagram of encoding “0” and “1” by the frequency shift keying method.
  

2) PPM (pulse position coding) method
  

In the pulse position programming mode, the time occupied by each binary number is the same, but the position of the mark pulse is different. The blank number in front and the mark after the mark means “1”, and the mark at the front and the blank number at the back means “0”. The following figure is a schematic diagram of encoding “0” and “1” using pulse position encoding.
  

3) PWM (pulse width coding) method
  

The pulse width coding method distinguishes “0” and “1” of binary numbers according to the width of the mark pulse.
  

The width of the mark pulse is “1”, the width of the mark pulse is “0”, and the number of bits between each binary number is equal to

This article explains the various principles and applications of infrared remote control

 
Scope of application of infrared remote control

Since the infrared remote control does not have the ability to pass through obstacles to control the controlled object like the radio remote control, when designing the infrared remote control for household appliances, it is not necessary to have every set (transmitter and receiver) like the radio remote control. There must be different remote control frequencies or codes (otherwise, the wall will control or interfere with the neighbor’s household appliances), so the infrared remote control of similar products can have the same remote control frequency or code, and there will be no remote control signal “drop-in” Case. This provides great convenience for mass production and popularizing infrared remote control on household appliances. Since infrared light is invisible light, it has little impact on the environment, and the wavelength of infrared light fluctuation is much smaller than that of radio waves, so infrared remote control will not affect other household appliances, nor will it affect nearby radio equipment.

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