how to convert byte array to floating point number

Projects Programming
1

I have newtek meter which gives 9 bytes of data and 4,5,6,7 bytes are important they are in ieee747 format so how can I convert this byte array into floating point number?

int incoming[9];
 int byte_array[4];
void setup() {
  // put your setup code here, to run once:
  
Serial.begin(9600);
pinMode(3,OUTPUT);
  }
  int i=0;String u;
   long speedLong;

void loop() {
  byte message[] = {0x01,0x04,0x00,0x46,0x00,0x02,0x90,0x1E};   //byte array to read frequency value from meter
  Serial.write(message,sizeof(message));     
  delay(1000); 
 
  int z=Serial.available();
Serial.println("Incoming bytes are:");
Serial.println(z);

  while (Serial.available() > 0)
    
  {

       incoming[i] =  Serial.read();

    Serial.print(incoming[i]);
 Serial.print('\t');
       i++;
  }
  int    j=0;
  for(i=3;i<=6;i++)                //sorting important byte array
  {
 Serial.println();
    byte_array[j]=incoming[i];
  Serial.print(byte_array[j]);

  Serial.print('\t');
  j++;
  }
  i=0;
  Serial.println();
  delay(2000);
}

The above code does the needful of getting the data and sorting the important bytes but, now I want to convert those improtant byte array into one floating point number which represents the parameter value how do i do that?

2

The subject has been discussed once or twice before.

For example, this search using keywords from your post...

https://www.google.com/search?q=convert+byte+array+into+floating+point+number+site:arduino.cc

Leads to this 8.5 year old thread...

http://forum.arduino.cc/index.php/topic,43670.0.html

3

I did try both of them but,in both cases I am not getting expected values i will post the code with output here:
Now I am just trying out with sample code sending byte array :0x42,0x48,0x23,0x8A and this value comes out to be 50.32 using IEEE734 format but the value I got are disaster

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);

}
union {
   byte b[4];
   float fval;
} u;
float velocity;
long speedLong;  

void loop() {
  byte incoming[4]={0X42,0X48,0X23,0X8A};
  // put your main code here, to run repeatedly:
  for(int i=0;i<=3;i++)
  {
 Serial.print(incoming[i],HEX); // prints the byte in hex
u.b[i] = incoming[i];   //using union 
 speedLong = (speedLong << 8) | incoming[i];  
  }

velocity = u.fval;  //should give floating point value 
Serial.println("Value got from method 1: ");
Serial.print('\t');
Serial.println(velocity);
Serial.println("Value got from method 2: ");
Serial.print('\t');
Serial.println(speedLong);
delay(200);

}

ouput:

4248238AValue got from method 1: 
	-0.00
Value got from method 2: 
	1112023946

And I have tried both the methods any suggestions how I could proceed?

4

oh.. I got it right finally!!!!!
instead of sending as: { 0X42,0X48,0X23,0X8A};
we must send:{0X8A,0X23,0X48,0X42};
worked like charm only using union but not using the other method

5

ddk1:
oh.. I got it right finally!!!!!
instead of sending as: { 0X42,0X48,0X23,0X8A};
we must send:{0X8A,0X23,0X48,0X42};

Yes, as you've found the float must be stored low byte first.

That "second method" is not anything close to what you want. It is not even casting it to a float, but rather to a long integer. All that will give you is the bit pattern of the float, but stuffed into a long integer, so don't expect it to make any sense.

If you want to have another way to do it then use the pointer typecast method.

byte incoming[4]={0X8A,0X23,0X48,0X42};
float velocity = *( (float*) incoming );
6

IEEE747?
IEEE734?