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What we need to learn today isAD/DA转换,That is, the conversion between digital signals and analog signals.To convert analog signal to digital signal we use adjustable resistor、Photoresistors and thermistors are implemented,The photoresistor is less than100时（较暗）,D1灯会自动亮;And the conversion of digital signal to analog signal we use to achieveDABreathing light to show.

成果展示

硬件知识

介绍

AD（Analog to Digital）：模拟-数字转换,将模拟信号转换为计算机可操作的数字信号.
DA（Digital to Analog）：数字-模拟转换,将计算机输出的数字信号转换为模拟信号.
AD/DA转换打开了计算机与模拟信号的大门,极大的提高了计算机系统的应用范围,也为模拟信号数字化处理提供了可能.

硬件电路模型

AD：It is to convert the voltage quantity into a digital quantity.
DA：其实有点类似于PWM,Finally it goes through a low pass filter,就能实现效果了.

AD转换通常有多个输入通道,用多路选择开关连接至AD转换器,以实现AD多路复用的目的,提高硬件利用率
AD/DA与单片机数据传送可使用并口（速度快、原理简单）,也可使用串口（接线少、使用方便）
可将AD/DA模块直接集成在单片机内,这样直接写入/读出寄存器就可进行AD/DA转换,单片机的IO口可直接复用为AD/DA的通道

电路

这是一个简单的AD芯片（ADC0809）,First select the analog switch,之后进行AD转换,And then output through the buffer,就可以了.

DA

这是一个简单的DA芯片（ADC0832）,首先输入数据,The registers are controlled by the control circuit,最后通过一个DAThe converter output becomes.

运算放大器

运算放大器（简称“运放”）It is an amplifying circuit unit with a very high magnification.A differential amplifier is integrated inside、电压放大器、Power amplifier three-stage amplifier circuit,is a performance complete、Powerful general-purpose amplifier circuit unit,Because of its wide application,It now appears in the circuit diagram as a basic circuit element
There are circuits that can be formed by operational amplifiers：电压比较器、反相放大器、同相放大器、电压跟随器、加法器、积分器、Differentiators, etc
Methods of Analysis for Operational Amplifier Circuits：虚短、虚断（under negative feedback conditions）

运放电路

电压比较器

This is what the voltage comparator does,当+大于-的时候,输出VCC,当-大于+的时候,输出GDN.

反向放大器

This conclusion can be obtained by analyzing virtual short and virtual segments.

同向放大器

电压跟随器

DA原理

T型电阻网络DA转换器

The specific process of this will not be described in detail,We just need to know that each switch is equivalent to each bit,At that time, you only need to know which switches are closed to know how many times the magnification is.

PWM型DA转换器

The effect of this is to filter out the communication,into a DC voltage.

AD原理

逐次逼近型AD转换器

逐次逼近型ADThe principle of the converter is throughDACConstantly changing to compare with the input voltage,until a suitable voltage is found,Just output the corresponding digital quantity.

AD/DA性能指标

分辨率：指AD/DA数字量的精细程度,通常用位数表示.例如,对于5V电源系统来说,8位的AD可将5V等分为256份,即数字量变化最小一个单位时,模拟量变化5V/256=0.01953125V,所以,8位AD的电压分辨率为0.01953125V,AD/DA的位数越高,分辨率就越高
转换速度：表示AD/DA的最大采样/建立频率,通常用转换频率或者转换时间来表示,对于采样/输出高速信号,应注意AD/DA的转换速度

XPT2046

时序

CS作为片选,Used to select different devices,然后是DCLKA rising edge is a transmit,Falling edge is read,DOUTis the read value.

代码

// XRT2046.c
#include <REGX52.H>
#include "Delay.h"

//引脚定义
sbit XPY2046_DIN=P3^4;
sbit XPY2046_CS=P3^5;
sbit XPY2046_DCLK=P3^6;
sbit XPY2046_DOUT=P3^7;

/**
  * @brief  ZPT2046读取AD值
  * @param  Command 命令字,范围：头文件内定义的宏,结尾的数字表示转换的位数
  * @retval AD转换后的数字量,范围：8位为0~255,12位为0~4095
  */
unsigned int XPT2046_ReadAD(unsigned char Command)
{
	unsigned int ADValue = 0;
	unsigned char i;
	
	XPY2046_DCLK = 0;
	XPY2046_CS = 0;
	for(i=0;i<8;i++)
	{
		XPY2046_DIN=Command&(0x80>>i);
		XPY2046_DCLK=1;
		Delay(1);
		XPY2046_DCLK=0;
	}

	for(i=0;i<16;i++)
	{
		XPY2046_DCLK=1;
		Delay(1);
		XPY2046_DCLK=0;
		if(XPY2046_DOUT){ADValue|=(0x8000>>i);}
	}
	XPY2046_CS=1;
	if(Command & 0x08){
	return ADValue>>8;
	}else
	return ADValue>>4;
}

// main.c
#include <REGX52.H>
#include "LCD1602.h"
#include "Delay.h"
#include "XPT2046.h"

unsigned int ADValue1 = 0,ADValue2 = 0,ADValue3 = 0;

sbit LED = P2^0;

void main(){
	LCD_Init();
	LCD_ShowString(1,1,"ADD  NTC  GR");
	while(1){
		ADValue1 = XPT2046_ReadAD(XPT2046_XP_8);//读取AIN0,可调电阻
		LCD_ShowNum(2,1 ,ADValue1,3);
		ADValue2 = XPT2046_ReadAD(XPT2046_YP_8);//读取AIN1,热敏电阻
		LCD_ShowNum(2,6 ,ADValue2,3);
		ADValue3 = XPT2046_ReadAD(XPT2046_VBAT_8);//读取AIN2,光敏电阻
		LCD_ShowNum(2,11 ,ADValue3,3);
		if(ADValue3 < 100){// The photoresistor is less than 100（较暗）just shine
			 LED = 0;
		}else{
			 LED = 1;
		}
	}
}

DA

//main.c
#include <REGX52.H>
#include "Delay.h"
#include "Time0.h"

sbit DA = P2^1;

unsigned char Counter,Compare;//计数值和比较值,用于输出PWM
unsigned char i;

void main(){
	Timer0_Init();
	while(1){
for(i=0;i<90;i++)
		{
			Compare=i;			//设置比较值,改变PWM占空比
			Delay(10);
		}
		for(i=90;i>0;i--)
		{
			Compare=i;			//设置比较值,改变PWM占空比
			Delay(10);
		}
	}
	
}

void Timer0_Routine() interrupt 1
{
	static unsigned int T0Count;
	TL0 = 0xAD;		//设置定时初始值
	TH0 = 0xFF;
	Counter++;
	Counter%=90;
	if(Counter < Compare){
		DA = 1;
	}else
	DA = 0;
}