STM32 infrared remote control

#STM32 - infrared remote control

Working principle of infrared remote control

Basic knowledge of light

The nature of light ： The essence of light is electromagnetic wave , Its propagation is essentially a particle vibration . In broad sense , Light refers to all electromagnetic spectra . In a narrow sense, light is an electromagnetic wave that human eyes can see , Also known as visible light ,.
The wavelength of light ： It refers to the distance of wave propagation in a vibration period . The wavelength of light is determined by the frequency of light and the medium of propagation , When light passes through different media , The frequency does not change while the wavelength changes
The color of light ： It is determined by its wavelength , Each color has its own wavelength , The visible light that people's eyes can see is arranged from long wavelength to short wavelength , Red... In turn 、 orange 、 yellow 、 green 、 green 、 blue 、 purple .

Visible light ：

​ The entire electromagnetic spectrum of light includes radio waves 、 Infrared 、 UV and X Rays, etc . They have different wavelengths , Where the wavelength is 380~760 Between nanometers is general visible light . Red... In turn 、 orange 、 yellow 、 green 、 green 、 blue 、 purple . Light with shorter wavelength than violet light is called ultraviolet , Light with a wavelength longer than red light is called infrared .

Infrared ：

​ It is an electromagnetic wave with a wavelength between microwave and visible light , The wavelength is 1mm To 760 nanometer （nm） Between , Non visible light longer than red light .
​ Above absolute zero （-273.15℃） All substances can produce infrared . Modern physics calls it thermal rays . We call the radiation beyond red light infrared （ Beyond violet light is ultraviolet ）, Human eyes cannot see .

Infrared communication

Wireless remote control technology ：

Also known as remote control technology , It refers to the realization of remote control over the controlled target , In industrial control 、 Aerospace 、 It is widely used in the field of household appliances .

infrared remote control ：

​ It's a wireless 、 Non contact control technology , Have strong anti-interference ability , Reliable transmission of information , Low power consumption , The cost is low , It is easy to realize , It is widely used by many electronic devices, especially household appliances , And more and more applied to computer and mobile phone systems .

Infrared communication ：

​ Is to transmit data through infrared . The transmitter sends an infrared signal , The receiver receives the signal and analyzes it . The transmitter matches the receiver . The emitter ： remote control .

Infrared remote control ：

​ The infrared remote control uses an infrared light-emitting diode , Infrared light is used as the carrier to transmit the key information to the device at the receiving end . Infrared light is invisible to human eyes , Therefore, the use of infrared remote control will not affect human vision （ You can turn on the mobile camera , Press... With the remote control towards the camera , You can see the infrared light emitted by the remote control ）.

signal modulation ：

​ There are many infrared light sources in the daily living environment , The sun 、 Candle fire 、 Incandescent lamp 、 Even our bodies . These infrared light sources may interfere with our receiving equipment , In order to shield interference , Receive only valid messages , We need to use modulation .

​ Through modulation, we can convert the specified digital signal into infrared light of a specific frequency for transmission , The modulation carrier frequency is usually in 30khz To 60khz Between , Most of them use 38kHz, Infrared light is transmitted at a fixed frequency , First, it is modulated and then transmitted .

Infrared receiver ：

​ Infrared receiver is a kind of receiver that can receive infrared signals and independently complete the receiving, output and TTL Level signal compatible devices , The volume is similar to that of an ordinary plastic sealed triode , Suitable for all kinds of infrared remote control and infrared data transmission .

Signal demodulation ：

​ Demodulation is to convert analog signals into digital signals . After the infrared receiver receives the infrared signal from the external transmitter , Will analyze the signal according to the fixed protocol , And convert it into digital signal output .

NEC protocol

NEC Characteristics of the agreement

8 Bit address code , 8 Bit command code
Complete transmission of address code and command code twice , To improve reliability -------- Send an address code , Send another address inversion , Whether the inverse code is equal to the source code .
Pulse length modulation
38KHz Carrier frequency
Bit time 1.12ms or 2.25ms, distinguish 0,1 The overall wavelength of .

First, the transmitter sends a series of waveform start codes , With 9ms Low level plus 4.5 High level of , Only after receiving the start code will the following be received 32 Bit data , Transmit if bit 560us Low level plus 560us High level is a logic 0, If 560us Low level plus 1690us High level is a logic 1,（Data Format ：Address + ~（Address） + Command + ~(Command）, If you keep pressing the key, a repeat code , Repeat the previous action .

Infrared circuit analysis

Altogether 3 Follow the line GND Grounding , One is a data cable PG8, A piece of VCC,IRDA For infrared receivers ,

Infrared example

The experiment purpose

Press the remote control button , The host receives the signal through the infrared receiver and decodes , Identify the command code of the key , Print out the corresponding key symbol