Introduction to 51 single chip microcomputer - LED light

1. LED

1.1. What is? LED？

LED（light-emitting diode）, Light emitting diodes , Be commonly called LED Small lights , It is made of gallium phosphide （GaP） And other semiconductor materials 、 A luminous display device that can directly convert electric energy into light energy . When LED There is a... Inside When the constant current passes , It will glow , Different LED Can emit different colors of light , Common ones are red 、 Yellow, etc , Pictured ：

About LED The outline features mainly describe the following points .
（1） monochrome LED The color of the shell indicates its luminous color .LED The shell of is transparent .
（2） monochrome LED Only two pins , These two pins are positive 、 Negative pole . Multicolor LED by 3 Root pin .
（3）LED The appearance is very distinctive , So you can easily identify LED.

1.2.LED The type of

1.3.LED Main parameters of

1. Electrical parameters ：
   （1） Forward operating current IF. It refers to the forward current value when the LED normally emits light . The working current of LED is generally 10～20mA.
   （2） Forward working voltage UF. It is the forward working voltage at both ends of the LED under a given forward current . Usually in IF=20mA When measuring , The forward working voltage of the LED is 1.4～3V . When the outside temperature rises , The forward operating voltage of the LED will drop .
   （3） v - Safety features . It refers to the LED voltage And current .

2. Limit parameters ：
   （1） Allowable power consumption Pm. It is the maximum value of the product of the forward DC voltage applied to both ends of the LED and the current flowing through it , When this value is exceeded, the LED is heated 、 damage .
   （2） Maximum forward DC current IFm. It is the maximum forward DC current allowed , Exceeding this value will damage the diode .
   （3） Maximum reverse voltage URm. It is the maximum reverse voltage allowed , Beyond this value, the LED may be hit Wear damage .
   （4） The work environment topm. It is the ambient temperature range in which the LED can work normally . Below or above this temperature range , The LED will not work properly , The efficiency is greatly reduced .

1.4.LED The main characteristics of

1. v - Safety features
   LED And the voltage of ordinary diode - Safety characteristics are similar , It's just LED The forward conduction voltage of is large . Small current LED The reverse breakdown voltage of is very small , by 6V To more than ten volts , Smaller than ordinary diodes . The picture below shows LED Positive volt - Safety characteristic curve .
   

The picture below is LED v - Safety characteristic curve , It contains forward and reverse characteristics .LED It has the input voltage similar to the general semiconductor triode - Safety characteristic curve .

About volt - Each section of the safety characteristic curve is described as follows .
（1）OA paragraph . This is a positive dead band .UA For opening LED Luminous voltage .
（2）AB paragraph . This is the workspace . In this section , Generally, as the voltage increases, the current also increases , The luminous intensity also increases .

In this section, special attention should be paid to , Without any protection , When the forward voltage increases to a certain value , that LED Forward voltage decrease of , And the forward current increases . If there is no protection circuit , It will burn out due to the increase of current LED.

（3）OC paragraph . This is the reverse deadband , Led plus reverse voltage does not emit light （ Don't work ）, But there is a reverse current . This reverse current is usually very small , Generally within a few microamps . stay 1990～1995 year , The reverse current is set as 10μA; stay 1996～2000 year , The reverse current is set as 5μA, At present, the reverse current is generally at 3μA following , But basically 0μA.
（4）CD paragraph . This is the reverse breakdown region ,LED The reverse voltage of one Do not exceed 10V, The maximum shall not exceed 15V. Over this voltage , Reverse breakdown will occur , Led scrapping .

In this section ,LED There is a large reverse breakdown current （ A few milliamps ）. This breakdown is not a thermal breakdown , No damage , Some AC outlets 、 The AC indicator light on the AC power switch uses LED, During the negative half cycle of alternating current LED Is working in this section .

2. Forward and reverse resistance characteristics
   LED The forward and reverse resistances are much larger than those of ordinary diodes , Understanding this point has important guiding significance for detecting diodes .
3. Relation between working current and relative luminous intensity
   The following figure shows the characteristic curve of the relationship between the working current and the relative luminous intensity of the LED . about Red LED for , When the forward working current increases, the relative luminous intensity also increases , When the working current reaches a certain level , The curve flattens （ saturated ）, It indicates that the relative intensity of luminescence tends to be saturated ; about green LED for , The working current increases , The relative intensity of luminescence increases , But there is no saturation .
   
4. Relationship between luminous intensity and ambient temperature
   The following figure shows the characteristic curve of the relationship between the luminous intensity of the LED and the ambient temperature . The lower the temperature , The greater the luminous intensity . When the ambient temperature rises , The luminous intensity will decrease significantly .
   
   5. Relationship between maximum allowable working current and ambient temperature
   The following figure shows the characteristic curve of the relationship between the maximum allowable working current and the ambient temperature . When the ambient temperature reaches a certain level , The maximum allowable operating current decreases rapidly , The result is zero , It means that when the ambient temperature is high ,LED Easier to damage , This is also LED Fear of scalding .
   
   6． Other characteristic curves

1.5.LED Pin polarity identification method

In order not to affect LED Normal lighting of , The model and polarity are not marked on the housing . So identify LED just 、 The negative pin mainly depends on the shape characteristics and the detection of the multimeter .

1. Pin length identification method
   The following figure shows the difference between positive and negative by pin length 、 Negative polarity pin LED, Its two pins are long and short , The long one is the positive pole , The short one is the negative pole .
   
2. Identification method of protruding key mode
   As shown in the figure below, the protruding key method indicates the positive pin method ,LED There is a protruding key on the base , by The nearest pin of this key is positive .
3. 3 Root pin LED Pin identification method
   The following figure shows a kind of 3 Root pin LED Pin distribution rule and internal circuit diagram . There are two different Color LED .K Is a common pin .
   The figure below shows another 3 Discoloration of root pin LED Schematic diagram of pin identification method , It has a tab , According to this feature, the pins can be easily determined .
   
4. 6 Root pin LED Pin identification method
   The picture below shows 6 Root pin LED Pin distribution rule and internal circuit diagram . There are two groups in it 3 Root pin LED.
   

1.6. Voltage control type and flashing type LED

1. Voltage control type LED
   LED It is a current control device , That is, it will glow when an electric current flows , When in use, the current limiting resistor with appropriate resistance shall be connected in series , For the convenience of use LED And current limiting resistor , When in use, it can be directly connected to both ends of the power supply , Thus, a voltage control type is formed LED. The following figure shows the voltage control type LED Physical diagram and internal circuit . Voltage control type LED The luminous color of has red 、 yellow 、 Green, etc , The operating voltage has 5V、9V、12V、18V、 19V、24V common 6 Species specification , What is commonly used is BTV series .
   

2. Scintillation type LED
   Scintillation type LED It's a kind of CMOS Integrated circuits and LED Special light emitting devices composed of . The following figure shows a flashing type LED Physical diagram and internal circuit , It can be used for alarm indication and undervoltage 、 Overpressure indication, etc .
   
   The following figure shows the flashing type LED Internal circuit block diagram . Scintillation type LED When use , No need to connect other components , As long as the appropriate DC working voltage is applied to both ends of its pin （5V） It will flash , The commonly used scintillation LED is BTS series .

2. MCU control LED

Wrote so much LED Introduce , We are right. LED Should have a clear understanding , Now we begin to program the single chip microcomputer to control LED.

2.1. Light up a LED

2.1.1 Programming

First of all we have Proteus 8 Professional Build a circuit schematic diagram as shown in the figure

 In the picture R1 Current limiting resistance , Prevent excessive current from causing LED damage .

Then start writing programs . If you've learned c The language of words , It should be easy to program , It doesn't matter if you haven't learned it , Copy first .

#include<reg52.h> //  Header file containing special function register definitions 

sbit LED = P2^3 ;     //  Bit address declaration  , Be careful ：sbit  Must be in lowercase  ,P Capital must be written. 

void main()			  //  Any one of them c There must be only one program  main  function 
{
    					  // {}  In pairs , Here is the beginning and end of the program 
	LED = 0 ;		  //  A semicolon indicates the end of a statement ,"1" High level ,"0"  Indicates low level 
}

First, analyze the syntax of the program ：
（1）main Is the function name of the main function , Every c There must be only one program main function .
（2）void Is the return type of the function , This program has no return value , use void Express .
（3）{} Here are the beginning and end of the function , Do not omit .
（4） Every one of them c The statement is semicolon (;) end .
Logically , This is how the program is written , however There will be a problem in the practical application of single chip microcomputer . For example, the program space can accommodate 1000 Line code , But the actual program only uses 100 Line code , When the operation is finished 100 That's ok , While continuing to run , The first 101 Line program is not the program you want to run , It's an unknown thing , Once executed, the program may make mistakes , This may cause the single chip microcomputer to reset automatically , So you usually add an dead loop to your program , Let the program stay in the desired state , Don't run around , There are two ways to refer to ：
Method 1 ：

#include<reg52.h>

sbit LED = P2^3 ;

void mian()
{
    
	while(1)
	{
    
		LED = 0 ;
	}
}

Method 2 ：

#include<reg52.h>

sbit LED = P2^3 ;

void mian()
{
    
	LED = 0 ;
	while(1) ;
}

Program （1） The function of is to execute repeatedly "LED = 1" This sentence , Program （2） The function of is to execute "LED = 1" Then stop and wait .

2.1.2 Compilation of program

After programming , The program should be compile , Generate .hex The file can burn the program into the MCU , Before compiling , You need to check an option first , Click Project （Project）-> Target “ The goal is 1” set an option …（Options for Target ‘Target1’…） Pictured ：

Or click the shortcut icon in the box as shown in the figure

In the pop-up dialog , single click Output Options page , Check one of the Create HEX File , Then click OK （OK） button , Pictured ：

Once you set it up , Click Project （Project）-> compile （rebuild all target files） , Or click the shortcut icon shown in the following figure
After compiling , stay Keil Output below （Output） The corresponding prompt will appear in the window , Pictured ：
data = 9.0, It refers to that the program uses the internal 256 byte RAM In resources 9 Bytes .
code = 18 It means to use 8K Code Flash In resources 18 Bytes .
When prompted “ 0 Error(s) ,Warning(s) ” Indicates that the program has no errors and warnings , Will appear “ creating hex file from “LED”… ”, This means that a is generated from the current project HEX file , This is what you want to download to the MCU HEX file . If there are errors and warnings , Namely Error and Warning No 0, Then check the program , Found the problem , After the problem is solved, compile and generate HEX Can only be .
Here we are , The program compiles successfully , After that, the program is burned into the MCU .

2.1.3. Program burning

If you don't have hardware, you can use Proteus 8 Professional To simulate the program .
stay Proteus 8 Professional Double click the MCU that needs to burn the program , Click on the folder icon , Found compiled . hex file , Click to open , Pictured ：


Then you can start the simulation .

If you have a small partner with hardware equipment , have access to STC-ISP ——STC Series SCM download software , Burn the program into the development board , Pictured ：
Be careful ： because STC Series MCU needs cold start download （ Click download first , Then supply power to the single chip computer ）, So turn off the power switch on the development board first , Then click download （Download） Button , Then power on the development board , You can burn the program into the MCU .
The above figure shows that the successful operation means that the program has been burned into the single-chip microcomputer .

The figure above shows the simulation results in the simulation software .
thus , Light up a LED The experiment is finished .

2.2. Flashing light

stay 2.1. Light one in the LED Is to make “LED = 0” that will do , Put out one LED The procedure is also very simple “LED = 1”. Now it will go out and light up , So how to make LED Flashing ？ It's also very simple. , Delay for a few seconds after lighting and then turn off , Just keep repeating .

2.2.1. The time delay function

There are usually two ways to achieve delay ： One is Hardware delay , You need a timer / Counter , This method can improve CPU Work efficiency , It can also achieve accurate delay ; The other is Software delay , This method is mainly carried out by circulating body . Here we mainly study software latency .

In many cases , Timer / Counters are often used for other purposes , At this time, the software method can only be used to delay . Here are some methods of software delay .
Method 1 ：
Short delay ： Can be in C In the document, by using the tape _NOP_( ) Statement , Define a series of different delay functions , Such as Delay10us( )、Delay25us( )、Delay40us( ) Etc. are stored in a custom C In file , Call directly in the main program when necessary . Such as delay 10 μs The delay function of can be written as follows ：

void Delay10us()
{
    
	_NOP_( ) ;
	_NOP_( ) ;
	_NOP_( ) ;
	_NOP_( ) ;
	_NOP_( ) ;
	_NOP_( ) ;
}

Delay10us( ) Functions are used together 6 individual _NOP_( ) sentence , The execution time of each statement is 1 μs. Main function call Delay10us( ) when , First execute a LCALL Instructions (2 μs), And then execute 6 individual _NOP_( ) sentence (6 μs), Finally, we executed a RET Instructions (2 μs), Therefore, a total of 10 μs.
Method 2 ：
Loop empty statement delay ： Write an empty loop statement in the program , Let the SCM in the empty loop “ In a daze ”. Write about 1ms The code for is as follows ：

void delay_ms(int n)
{
    
	int i , j ;
	for( i = 0 ; i < n ; i ++ )
	{
    
		for( j = 0 ; j < 123 ; j ++) ;
	}
}

stay n by 1 when , The code probably runs 1ms about .
This delay method is the most commonly used method in imprecise delay .
Or both ：

void Delay1ms()		//@11.0592MHz  Crystal vibration is 11.0592MHz
{
    
	unsigned char i, j;

	_nop_();
	i = 2;
	j = 199;
	do
	{
    
		while (--j);
	} while (--i);
}

2.2.2. The realization of flashing lamp

We have learned how to write the delay function , You can start writing blinking lights .
Circuit schematic diagram and 2.1 The same as , The code is as follows ：

#include<reg52.h> //  Header file containing special function register definitions 

sbit LED = P2^3;     //  Bit address declaration  , Be careful ：sbit  Must be in lowercase  ,P Capital must be written. 

void delay_ms(int n)	  //  The time delay function   About time delay  n ms
{
    
	int i , j ;			  //  Define two integer variables  i,j
	for( i = 0 ; i < n ; i ++ )
	{
    
		for( j = 0 ; j < 123 ; j ++ ) ;			 
	}
}

void main()			  //  Any one of them c There must be only one program  main  function 
{
    					  // {}  In pairs , Here is the beginning and end of the program 
	while(1)
	{
    
		LED = 1 ;	  //  A semicolon indicates the end of a statement  "1" High level ,"0"  Indicates low level 
		delay_ms( 10 ) ;
		LED = 0 ;
		delay_ms( 10 ) ;
	}		  
} 

Simulation video link of the above program

2.3. Running water lamp

seeing the name of a thing one thinks of its function , The running water lamp is to light up one by one like running water , Extinguish one by one .
We first in Proteus 8 Professional The following schematic diagram is established in ：

The picture shows LED The public end is GND（ Low level ）, So the program should make P1 Port output high level , To light up LED.
The code is as follows ：

#include<reg52.h> // This file defines some special function registers of MCU 
#define uchar unsigned char // Declare and define data types 
#define uint unsigned int // Declare and define data types 

void delay(uint n)		//  The time delay function , About time delay  n ms
{
    
	uchar i,j;		// Define unsigned character variables  unsigned char  The data range of is 0~255（2^8 - 1）
	for(i = 0 ; i < n ; i ++)
	{
    
		for(j = 0 ; j < 123 ; j ++);
	}
}

void main()
{
    
	P1 = 0x00; //0000 0000  initialization P1 port , Make it output low level 
	while(1)
	{
    
		P1 = 0x01 ;   //0000 0001  namely P0^0 High level , The rest are low level 
		delay(200) ;
	   	P1 = 0x02 ;  // 0000 0010  namely P0^1 High level , The rest are low level 
		delay(200) ;
		P1 = 0x04 ;	 // 0000 0100  namely P0^2 High level , The rest are low level 
		delay(200) ;
	   	P1 = 0x08 ;  // 0000 1000  namely P0^3 High level , The rest are low level 
		delay(200) ;
		P1 = 0x10 ;	 // 0001 0000  namely P0^4 High level , The rest are low level 
		delay(200) ;
	   	P1 = 0x20 ;	  //0010 0000  namely P0^5 High level , The rest are low level 
		delay(200) ;
		P1 = 0x40 ;	 // 0100 0000  namely P0^5 High level , The rest are low level 
		delay(200) ;
	   	P1 = 0x80 ;  // 1000 0000  namely P0^6 High level , The rest are low level 
		delay(200) ;
	}
}

Or use the left shift method to write

void main()
{
    
	uint i ;     // Define an unsigned integer variable  unsigned int  The data range of is  0~65535(2^16 - 1)
	P1 = 0x00; //0000 0000  initialization P1 port , Make it output low level 
	while(1)  //  Dead cycle （ There is no end to the infinite cycle ）
	{
    
		for( i = 0 ; i < 8 ; i ++ )
		{
    
		 	P1 = ( 0x01 << i ) ;  // i = 1  Move left when 1 position ;i = 2  Move left when 2 position  ...  When  i= 8  Stop the cycle when  for  End of the function  .
			delay(200) ;
		}
	}
}

Simulation video link of the above program

Here is the left shift of the reference program, and the right shift refers to the... Of the variable 8 Bit binary numbers are shifted one bit to the left in turn , Or move one bit to the right and fill in the high or low position 0. such as , take 8 digit , Give Way 0000 0001 Cycle one bit left , Namely 0000 0010.