next topic »

[on:]

I have a temp sensor (LM335A) connected to analog pin 0. When converting the values to degress Celsius I got wrong sign if the temperature is -0,xx. For example:
-1,xx will be displayed as -1,xx  (OK)  but
-0,xx  will be displayed as 0,xx   (wrong, missing - sign when temp is 0,  something)
I have picked up the code from different examples in Arduinos examples, but because of lack of skills in this area I can't find the error in the code:

// *************************************************************************************          
unsigned int precision =100;
unsigned int frac;
double val;
double valr;
          
      client.print("Analog 0: ");
  val = analogRead(0);
  val = val - 10;             // calibration of LM335
  val = val * 0.48875;     // 5Volt/1023 * 100
  valr = val - 273.15;      // convert Kelvin to Celsius
  
    client.print(int(valr));  // prints the int part
    client.print(",");          // print the decimal point
    
    if(valr >= 0)
      frac = (valr - int(valr)) * precision;
    else
       frac = (int(valr)- valr ) * precision;
    int  frac1 = frac;
    while( frac1 /= 10 )
        precision /= 10;
    precision /= 10;
    while(  precision /= 10)
        client.print("0");
    client.print(frac,DEC) ;
    client.print(" &#176C");
    client.println("<br />");  

[Reply #1 on:]

try replacing:
 if(valr >= 0)
     frac = (valr - int(valr)) * precision;
   else
      frac = (int(valr)- valr ) * precision;

with      
      
 if(valr < 0.0){
    client.print('-');
    valr = -valr;
  }
  frac = (valr - int(valr)) * precision;

[Reply #2 on:]

Now I got a - but missplaced  .... 0,-42

[Reply #3 on:]

Can you post a version of the code that uses Serial so I can have a look and try running it?  Just replace your sensor code with a hard coded floating point value

[Reply #4 on:]

Here it comes, you have to change the different val statement:


void setup()
{

   Serial.begin(9600);
        
   }
 
void loop()
{
unsigned int precision =100;
unsigned int frac;
double val;
double valr;  
      

      
  val = 567;                // expected result = -0,91 (actual 0,-91)
//  val = 560;                // expected result = -4,33   (actual -4,-33)
//  val = 618;                // expected result = 24,01   (actual 24,01)
  val = val - 10;          // calibration of LM335
  val = val * 0.48875;     // 5/1023 * 100
  valr = val - 273.15;     // Kelvin to Celsius
    Serial.print("Analog 0: ");
    Serial.print(int(valr));  //prints the int part
    Serial.print(","); // print the decimal point
    
    if(valr < 0.0){
   Serial.print('-');
   valr = -valr;
 }
 frac = (valr - int(valr)) * precision;
    int  frac1 = frac;
    while( frac1 /= 10 )
        precision /= 10;
    precision /= 10;
    while(  precision /= 10)
    Serial.print("0");
    Serial.print(frac,DEC) ;
    Serial.print(" &#176C");
    
    }

[Reply #5 on:]

you need to print the integer part after you print the sign. try this:

Code:

void setup(){
  Serial.begin(9600);
}

void loop()
{
  unsigned int precision =100;
  unsigned int frac;
  double val;
  double valr;  


  val = 567;                // expected result = -0,91 (actual 0,-91)
  //  val = 560;                // expected result = -4,33   (actual -4,-33)
  //  val = 618;                // expected result = 24,01   (actual 24,01)
  val = val - 10;          // calibration of LM335
  val = val * 0.48875;     // 5/1023 * 100
  valr = val - 273.15;     // Kelvin to Celsius
  Serial.print("Analog 0: ");
  if(valr < 0.0){
    Serial.print('-');
    valr = -valr;
  }
  Serial.print(int(valr));  //prints the int part
  Serial.print(","); // print the decimal point
  frac = (valr - int(valr)) * precision;
  int  frac1 = frac;
  while( frac1 /= 10 )
    precision /= 10;
  precision /= 10;
  while(  precision /= 10)
    Serial.print("0");
  Serial.print(frac,DEC) ;
  Serial.print(" &#176C");
}

[Reply #6 on:]

It works, Thank you! ;D