Assemble or typecast byte array to float

Question

The serial port on my Arduino Mega is receiving 3 floats as bytes (total of 12 bytes, 4 per float) over serial. Unfortunately I cannot assemble the 4 Bytes in a float, as the serial monitor only displays

0.00

0.00

0.00 etc.

Here is the code:

void serialEvent2() {
  if (Serial2.available() > 11) {
    byte yawData[3];
    yawData[0] = Serial2.read();
    yawData[1] = Serial2.read();
    yawData[2] = Serial2.read();
    yawData[3] = Serial2.read();
    float yawAngle = *((float*)(yawData));
    Serial.println(yawAngle);

    byte pitchData[3];
    pitchData[0] = Serial2.read();
    pitchData[1] = Serial2.read();
    pitchData[2] = Serial2.read();
    pitchData[3] = Serial2.read();
    float pitchAngle = *((float*)(pitchData));

    byte rollData[3];
    rollData[0] = Serial2.read();
    rollData[1] = Serial2.read();
    rollData[2] = Serial2.read();
    rollData[3] = Serial2.read();
    float rollAngle = *((float*)(rollData));
  }
}

I made sure the data coming to Serial2 is not 0.

UPDATE: The initial mistake was my byte array not being sized correctly. I fixed it. The values I print are fine until after about a second, they get totally weird. Dropped bits/Bytes maybe? Seems odd because a sample sketch written in Processing works perfectly while taking the exact same input.

Answer 1

I tried the code below and it worked for me, don't miss the delay() part:

Sender Code:

void setup() {
  Serial.begin(9600);
}

void loop() {
    float yaw = 10.5;
    float pitch = 20.15;
    float roll = 100.10;
    float ypr[3];  
    ypr[0] = yaw;
    ypr[1] = pitch;
    ypr[2] = roll;
    Serial.write((byte*) ypr, 12);  // No new-line
    delay(1000);

}

Receiver Code:

void setup() {
  Serial.begin(9600);
}

void loop() {

}

void serialEvent() {
    if (Serial.available() == 12){
      byte yawData[4];
      yawData[0] = Serial.read();
      yawData[1] = Serial.read();
      yawData[2] = Serial.read();
      yawData[3] = Serial.read();
      float yawAngle = *((float*)(yawData));
      Serial.println(yawAngle);

      yawData[0] = Serial.read();
      yawData[1] = Serial.read();
      yawData[2] = Serial.read();
      yawData[3] = Serial.read();
      float yawPitch = *((float*)(yawData));
      Serial.println(yawPitch);

      yawData[0] = Serial.read();
      yawData[1] = Serial.read();
      yawData[2] = Serial.read();
      yawData[3] = Serial.read();
      float yawRoll = *((float*)(yawData));
      Serial.println(yawRoll);
    }
}

Results:

Answer 2

If you must do it that way I'd recommend using a union:

typedef union {
    float val;
    uint8_t bytes[4];
} floatval;

floatval v;
v.bytes[0] = Serial2.read();
v.bytes[1] = Serial2.read();
v.bytes[2] = Serial2.read();
v.bytes[3] = Serial2.read();
Serial.println(v.val);

A better solution is to just write and read the raw float data:

// Sender:
Serial.write((const char *)&myfloat, sizeof(float));

// Receiver
Serial2.readBytes((char *)&myfloat, sizeof(float));

Even better still is to define a struct which is the packet of data you wish to send:

typedef struct {
    float yaw;
    float pitch;
    float roll;
} attitude;

attitude myatt;
myatt.yaw = 14.9;
myatt.pitch = 23.4;
myatt.roll = 11.49;

Serial.write((const char *)&myatt, sizeof(attitude));

// receive:

attitude myatt;
Serial2.readBytes((char *)&myatt, sizeof(attitude));
Serial.println(myatt.yaw);
Serial.println(myatt.pitch);
Serial.println(myatt.roll);

Answer 3

try use memcpy, i think it might work:

void serialEvent2() {
  if (Serial2.available() > 11) {
    byte yawData[4];
    float yawAngle = 0;
    yawData[0] = Serial2.read();
    yawData[1] = Serial2.read();
    yawData[2] = Serial2.read();
    yawData[3] = Serial2.read();
    memcpy(&yawAngle, &yawData,sizeof(float));
    Serial.println(yawAngle);

    // same for others ...
  }
}

Answer 4

What if you write

yawData[3] = Serial2.read();
yawData[2] = Serial2.read();
yawData[1] = Serial2.read();
yawData[0] = Serial2.read();

i.e. you change the endianness of the representation