Strange behavior when compiler converts from float to double
I have an array:
float foo[3];
In the ino file I have to send one of them to the PID as input.
double output;
PID myPID(&input, &output, &target, 1, 0.0, 1.1, DIRECT);
...
void loop(){
input =foo[2];
myPID.Compute();
Serial.print(output); //output: "nan"
...
}
The PID is as follow:
PID::PID(double* Input, double* Output, double* Setpoint,
double Kp, double Ki, double Kd, int ControllerDirection)
It compiles but the output of the PID outvalue is nan.
However if I set the input to -1.2 then it works.
void loop(){
input =foo[2];
input = -1.2;
myPID.Compute();
Serial.print(output); //output: "1200"
...
}
How can I fix this? The compiler should auto convert double the float. As in Mega 2560. I have also tried: input =double(foo[2]); without any success.
EDIT:
Serial.print(foo[2]); //Prints -9.2
foo[2] = -9.2; // I manually set foo[2] to -9.2
xAngle = foo[2];
xPID.Compute(); //Computes perfectly.
I have to add that foo is in a custom library. This is so strange. Anyone got a clue about this?
sizeof(double); and sizeof(float); both will return 4 . Secondly, if you want to cast one type to another the syntax is (targetType)sourceType , so if you do that sort of a thing, your assignment should look like this
input =(double)foo[2];
or
input =(double)(foo[2]);
However, this is irrelevant in this case since doubles and floats are identical.
I think most likely the problem comes from the fact that your PID controller does not like whatever value you have in foo[2] given the parameters you set. Have you tried foo[2]=-1.2 before assigning input = foo[2]; ?