arduino中浮动变量的精度

Question

我从模拟输入的电压信号(A0引脚)和电流信号(以电压的形式)从模拟输入(A1引脚)，将它转换成数字，然后处理它，以获得Vrms，Irms和相位数据。然后我将其存储在"dataString“中，并将其写入SD卡。

我面临的问题是，在功率因数的浮点计算中，我做了一些错误的事情，因为它的答案被“显示为”1.00，而在4.97 (度)的角度上，我应该得到cos(4.97) = 0.9962 (附图) Image1。

虽然程序正在使用正确的值，即在进一步的计算中使用0.9962 (实数)，但我希望它能够在十进制之后正确地显示功率因数4点。这是我的程序代码

#include <SPI.h>
#include <SD.h>

#include <Wire.h>
#include "RTClib.h"

RTC_DS1307 RTC;
#include "DHT.h"

#define DHTPIN 8 
#define DHTTYPE DHT21
DHT dht(DHTPIN, DHTTYPE);

#define count 100

const int analogInPin1 = A1;
const int analogInPin0 = A0;

const int chipSelect = 10;

void setup()
{
  Serial.begin(115200);
        Wire.begin();
        RTC.begin();

      if (! RTC.isrunning()) {
        Serial.println("#RTC is NOT running!");
        // following line sets the RTC to the date & time this sketch was compiled
        // uncomment it & upload to set the time, date and start run the RTC!
       // RTC.adjust(DateTime(__DATE__, __TIME__));
      }
  analogReference(DEFAULT);
  Serial.println("#DHTxx test!");

  dht.begin();


  Serial.print("#Initializing SD card...");

  // see if the card is present and can be initialized:
  if (!SD.begin(chipSelect)) {
    Serial.println("#Card failed, or not present");
    // don't do anything more:
    return;
  }
  Serial.println("#card initialized.");
  Serial.println("#Date        Time           Vrms          Irms         Phase        Power_factor       Apparent_Power     Real_Power        Humidity         Temperature");


}

void loop()
{


  float sensorValue0[count];        
  float sumSensorValue0=0;
  float meanSensorValue0=0;
  float Vrms=0;
  sumSensorValue0=0;

  float sensorValue1[count];        
  float sumSensorValue1=0;
  float meanSensorValue1=0;
  float Irms=0;
  int i=0;
  sumSensorValue1=0;

  DateTime now = RTC.now();

  for(i=0;i<count;i++)
  {
    sensorValue1[i] = (analogRead(analogInPin1)*4.8)-3200; //4.8 mV (i.e. 0.0048 Volts)  per unit.. Vref/1024.. here Vref = 5 V ....//3.220 V = Offset
    sensorValue0[i] = (analogRead(analogInPin0)*4.8)-3200;

    sensorValue1[i] = sensorValue1[i]*sensorValue1[i];
    sensorValue0[i] = sensorValue0[i]*sensorValue0[i];
    sumSensorValue1+= sensorValue1[i];
    sumSensorValue0+= sensorValue0[i];
  }

  meanSensorValue1 = sumSensorValue1/count;
  meanSensorValue0 = sumSensorValue0/count;
  Irms = (sqrt(meanSensorValue1)*0.06); //60/1000 = 0.06 Calibrating 60 Ampere/1 Volt to give us the value for X amperes
  Vrms = (sqrt(meanSensorValue0)*0.3565); // Multiplying with 356.5(the product of ratios of 9V and 12 V transformer) gives the measured voltage in mV.. dividing by 1000 to bring it to Volts from mV
  float appPower;
  appPower = Vrms*Irms;

float Vsense=0;
float LastVsense=0;
float Isense=0;
float LastIsense=0;
float phase;
float mean_phase=0;
float counter=0;
unsigned long timer;

 for(int i=0;i<200;i++)
  {
  // put your main code here, to run repeatedly:
 Isense=analogRead(A1)*4.8-3200;
 Vsense=analogRead(A0)*4.8-3220;
 if(Vsense>= 0 && LastVsense<0  && Isense<0 )
   { 
  timer = micros();
  do{
    Isense=analogRead(A1)*4.8-3200;
  }while(!(Isense>=0));
    timer = micros()-timer;
    phase = (timer*360.0)/20000.0;
    mean_phase+=phase;
    counter+=1.0;
    }else;

    if(Isense >= 0 && LastIsense < 0  && Vsense < 0 )
   { 
  timer = micros();
  do{
    Vsense=analogRead(A0)*4.8-3200;
  }while(!(Vsense>=0));
    timer = micros()-timer;
    phase = (timer*360.0)/20000.0;
    mean_phase+=phase;
    counter+=1.0;
    }else;

LastIsense = Isense;
LastVsense = Vsense;

}
  mean_phase= mean_phase/counter;


  float realPower;
  float powerFactor;
  float phase_rad= mean_phase*PI/180.0;
  powerFactor =cos(phase_rad); //phase converted to radian for cosine function
  realPower = Vrms*Irms*powerFactor;

   String dataString = "";

  float h = dht.readHumidity();
  float t = dht.readTemperature();

   if (isnan(t) || isnan(h)) {
    Serial.println("#Failed to read from DHT");
  } else {
    dataString+=now.year(), DEC;
    dataString+="/";
    dataString+=now.month(), DEC;
    dataString+="/";
    dataString+=now.day(), DEC;
    dataString+=" ";
    dataString+=now.hour(), DEC;
    dataString+=":";
    dataString+=now.minute(), DEC;
    dataString+=":";
    dataString+=now.second(), DEC;
    dataString+="         ";
    dataString+=Vrms;
    dataString+="         ";
    dataString+=Irms;
    dataString+="         "; 
    dataString+=mean_phase;
    dataString+="         ";
    dataString+=powerFactor;
    dataString+="                 ";
    dataString+=appPower; 
    dataString+="                 ";
    dataString+=realPower;
    dataString+="         ";
    dataString+=h;
    dataString+="         ";
    dataString+=t;

  }
  // open the file. note that only one file can be open at a time,
  // so you have to close this one before opening another.
  File dataFile = SD.open("datalog.dat", FILE_WRITE);

  // if the file is available, write to it:
  if (dataFile) {
    dataFile.println(dataString);
    dataFile.close();
    // print to the serial port too:
    Serial.println(dataString);
  }
  // if the file isn't open, pop up an error:
  else {
    Serial.println("#error opening datalog.dat");
    }

  delay(10000);
}

Answer 1

虽然程序在进一步的计算中使用了正确的值，即0.9962 .

这表明问题在您的打印代码中。

更具体地说，我怀疑这句话可能会引起麻烦：

dataString+=powerFactor;

您正在使用String类，因此WString.cpp是相关的文件。

如果我们检查它，我们会发现在第409行(至少在我的Arduino版本中，1.6.7IIRC中)，+操作符是为浮点数声明的，它只是调用concat(float)，这可以在第323行中找到：

unsigned char String::concat(float num)
{
    char buf[20];
    char* string = dtostrf(num, 4, 2, buf);
    return concat(string, strlen(string));
}

如果您阅读dtostrf文档，您将发现这是将一个双(浮点数被提升)转换为一个宽度为4位和2位精度的字符串。

解决这一问题的最简单方法是使用dtostrf将浮点数转换为具有所需精度的字符串，然后将该字符串附加到string实例中。