（15） Infrared communication

In this section, we mainly explain the content of infrared communication , We passed one of our infrared emitters ( Like a remote control ) To the... Connected to the infrared receiver 51 Single chip computer sends an infrared signal , After receiving the signal, the infrared receiver will display the specific key value on our digital tube .

About infrared light ：

The order of light that human beings can see from long to short is rainbow seven colors ： red , orange , yellow , green , green , blue , purple . The wavelength range of red light is 0.62~0.76um; The wavelength range of violet light is 0.38~046um; Light with shorter wavelength than violet light is called ultraviolet , Light longer than red light is called infrared . Infrared remote control uses the wavelength of 0.76um~1.5um Between the infrared ray to control the signal . And because infrared light does not have the ability to penetrate the wall , Although it is a drawback , But it can also be called its advantages , This also provides conditions for large-scale use , Every household can use the same frequency infrared remote control without channel changing .

Infrared remote control communication is generally composed of two infrared transmitting devices and infrared receiving devices

About infrared emitting devices , That is what we call the remote control , The common carrier frequency is 38kHz, This is due to the 455kHz Frequency dependent , At the transmitter, divide the integer frequency , It's usually 12 frequency division , So the frequency of the transmitter is 455/12=37.9, About equal to 38, Of course, some infrared frequencies are 36kHz,40kHz etc. , Generally, this frequency is determined by the frequency of the transmitter . There are two forms of binary pulse code between two devices , It means that there are two forms to represent high pulse and low pulse , What I am using now is NEC Protocol Of PWM code , This code is characterized by 8 Bit address and 8 Bit instruction length , Address and command are transmitted twice ,PWM Pulse position modulation , It is represented by the duty cycle of the transmitted infrared carrier 0 and 1, What does that mean ？ Every logic 0 perhaps 1 It's all about 560us Is a basic unit , If we want to express a logic 1, Then we need to send a 560us Pulse and three 560us Low level of , If we want to express a logic 0, Just one 560us And a 560us Low level of . The receiving of the infrared receiving head is just opposite to the logic of the transmission , This means that the infrared transmitter emits a high level , Then our infrared receiver will receive a low level , And you send a low level and you receive a low level , As for the principle, we don't need to understand , It's actually an agreement . We just talked about the representation of high and low levels , So how do we send a data ？ The process of infrared transmission is actually the transmission of several codes , Its data format is ： Pilot code , Address code , Address inversion , Control code , Control the irony . The pilot code consists of a 9ms Low level and a 4.5ms High level composition of , The rest are made up of 8 A composition . The meaning of inverse code is to verify whether you receive correctly . Increase the reliability of transmission .NEC Code also specifies the serial code , It is used to count if you haven't released it after you press it , You can count the length or number of keystrokes by counting the number of consecutive codes . You can check the specific serial number .

Hardware ：

        This is mine 51 MCU infrared receiving module content , My single chip computer has passed P32 Communicate with the infrared module , See if there is an infrared transmitter to send content to the infrared module

  Software ：

        our P32 It happens to be an interrupt pin , We can determine whether the infrared signal is sent by determining whether there is a pilot code , There is a bad thing about this code , It can't be said that , This is also the limitation of SCM . That is to write all the judgment contents into the interrupt , This can easily affect the normal operation of other programs in large programs , Because the interruption time is too long , But if not written in interrupt , It may also be affected by other interruptions . But there will be no problem with this program , After all, only such a program is running . So there is no problem writing it in the interrupt . We use the digital tube to display the address code we received . The code is as follows ：

#include "reg52.h"
#include "main.h"
#include "ir.h"
sbit IRIN = P3^2;
int Time;
unsigned char IrValue[4] = {0,0,0,0};

void delay(int xms){
	while(xms--);
}

void ir_init(){
	IT0 = 1;
	EX0 = 1;
	EA = 1;
	IRIN = 1;
}

void ir_check(){
 	unsigned char j,k;
	unsigned short err;
	Time=0;					 
	delay(700);	
	if(IRIN==0)	
	{	 
		
		err=1000;				
		while((IRIN==0)&&(err>0))  		
		{			
			delay(1);
			err--;
		} 
		if(IRIN==1)			
		{
			err=500;
			while((IRIN==1)&&(err>0))
			{
				delay(1);
				err--;
			}
			for(k=0;k<4;k++)		
			{				
				for(j=0;j<8;j++)	
				{

					err=60;		
					while((IRIN==0)&&(err>0))
					{
						delay(1);
						err--;
					}
					err=500;
					while((IRIN==1)&&(err>0))	 
					{
						delay(10);	 //0.1ms
						Time++;
						err--;
						if(Time>30)
						{
							return;
						}
					}
					IrValue[k]>>=1;	 
					if(Time>=8)			
					{
						IrValue[k]|=0x80;
					}
					Time=0;									
				}
			}
		}
		if(IrValue[2]!=~IrValue[3])
		{
			return;
		}
	}			
}
void main(){
	ir_init();
	while(1){
		display(IrValue[2]);
	}
}
void ir_interrupt() interrupt 1{
	IT0 = 0;
	ir_check();
	IRIN = 1;
	IT0 = 1;
	
}

The code of the nixie tube is as follows

#include "reg52.h"
#include "main.h"
sbit LSA = P2^2;
sbit LSB = P2^3;
sbit LSC = P2^4;
unsigned char code smgduan[17]={0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,
					0x7f,0x6f,0x77,0x7c,0x39,0x5e,0x79,0x71};// Show 0~F Value 
void display(int val){
	char temp[3];
	int i;
	

		temp[0] = 0x76;	
		temp[1] = smgduan[val % 16];
		temp[2] = smgduan[val / 16];

	for(i = 0;i < 3;i++){
		switch(i){
			case 0:
				LSA = 0; LSB = 0; LSC = 0;
				break;
			case 1:
				LSA = 1; LSB = 0; LSC = 0;
				break;
			case 2:
				LSA = 0; LSB = 1; LSC = 0;
				break;
		}
		P0 = temp[i];
		delay(100);
		P0 = 0x00;
	} 
}

The two header files are as follows ：

#ifndef _MAIN_H_
#define _MAIN_H_

void delay(int xms);
#endif

#ifndef _IR_H_
#define _IR_H_
 void display(int val);
#endif