（3） Dynamic digital tube

        This chapter will talk about the relevant contents of dynamic digital tube , In fact, from the front gpio And buzzer , We basically just learned a little about a single gpio Use , In this section, let's review the whole group gpio Operation method . Before memories , You still need to add some knowledge to .

1. About digital tube

        First, about the digital tube , In fact, it's very simple , A digital tube actually means that there are many led The lights need to be operated at the same time , It's a group gpio All to low level or high level , There is actually a little distinction here , When designing your digital tube, do you connect all the cathodes together or do you connect all the anodes of the digital tube together , If all the anodes are connected together, it means a common anode digital tube , On the contrary, it is a common cathode digital tube , See your chip manual for this , Or use a multimeter to measure , See the following development for the test method , My digital tube is a common cathode digital tube , If we connect this common cathode to the ground , And we give them each anode to high and low levels , In fact, you can display a complete number . The multi digit nixie tube is a multi digit nixie tube , But its structure is basically similar to that of using multiple one bit digital tubes , Just take my 4 Take the digital tube for example , See the picture below ：

2. Hardware       

        From the above figure, we can see that the top here is the common cathode of each digital tube , We generally call this section route selection , We just need to select one and give it a low level , Then all the other lines below us give us some high levels for the bits we want , Then our digital tube can light up and become the number we want . You may notice that we give a Level corresponds to a Bit will be lit . And about 74HC245 chip , The first thing we should say about each chip is to check its chip manual , First of all, why do we need 74HC245 This chip ？ In fact, this is very similar to what we talked about in the previous section , That is to say 51 The driving ability of single chip microcomputer is not good , We need to add drive capability to it , Here we add 74HC245 Why , We don't need to configure it , Because we have made the corresponding configuration on the hardware , to DE Pin a low level to enable , That means making the chip work , And vcc If you give a high level, you can start from A To B Output , In this case, the hardware of the digital tube is almost the same , But the above line selection is not directly connected to gpio above , Instead, I chose to receive 38 On the decoder , As shown in the figure below

         In fact, the best way is to see it at this time 38 Decoder chip manual , I'll just talk about its features here , Let's just copy its truth table .

         there A0,A1,A2 Corresponding to the above figure respectively A,B,C,E1,E2,E3, They correspond to each other G1,G2A,G2B, Because of what we have here E1,E2,E3 The status has been established , Then we just need to go through A,B,C To complete the function , As shown in the figure above ,L For low level ,H For high level ,X Represents any state , Because of our E1,E2,E3 The state of has been determined , So let's start with the fourth line , It means that we pass through A、B、C You can choose Y The state of , Let the corresponding Y Bit output low level , You can select the corresponding nixie tube .

3, Software

        We are now writing a simultaneous display program for the nixie tube 0 To 7 The relevant contents of the data , The code is as follows ：

#include <reg52.h>
sbit LSA = P2^2;
sbit LSB = P2^3;
sbit LSC = P2^4;
unsigned code smgduan[17]={0x3f,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,
					0x7f,0x6f,0x77,0x7c,0x39,0x5e,0x79,0x71};//0x0~0xf
/* Delay time */
void delay(int x){
	while(x--);
}
void main(){
	int i;

	while(1){
		for(i = 0;i < 8;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;
				case 3:
					LSA = 1; LSB = 1; LSC = 0;
					break;
				case 4:
					LSA = 0; LSB = 0; LSC = 1;
					break;
				case 5:
					LSA = 1; LSB = 0; LSC = 1;
					break;
				case 6:
					LSA = 0; LSB = 1; LSC = 1;
					break;
				case 7:
					LSA = 1; LSB = 1; LSC = 1;
					break;
			}
			P0 = smgduan[i];
			delay(10); // Delay 
			P0 = 0x00; // Shadow elimination 
		}
	}
}

        In addition to the previous introduction to our program , The most important one is about delay , The delay should not be too long , If it is too long, it will not be displayed at the same time , In fact, our simultaneous display is time-sharing , But our eyes are not so fast , It looks like it is displayed at the same time , It is the same reason that we watch TV , The later shadow elimination is mainly for , Eliminate residual shadow . And the array of numbers is directly calculated by me one by one .

4. Expand the content

        About how to use a multimeter to measure the voltage of a digital tube , The multimeter uses the gear of the voltmeter , We can choose any two pins to measure the voltage between them , As long as the voltage between them is 1.5v, Then connect one end to the other pin , You can know whether the digital tube is a common anode or a common cathode , In fact, there is no multimeter. In fact, after analyzing the circuit diagram, it will come out , You can see from my circuit diagram that it is a common cathode , I still can't , Turn to the corresponding manual , It's OK, too .