Delays in loop() cause erratic PID.compute() values about arduino-pid-library HOT 4 OPEN

Hm, and then there's this post on your original blog

Coding Badly says: I think moving the time calculations out of Compute is a good idea but it does create a potential pitfall for new users. The calculations will not be accurate if more than SampleTime has elapsed between calls. This could be difficult (or impossible) to debug. I suggest adding a check for “(grossly) exceeded SampleTime”. If the SampleTime has been exceeded, set a flag. This gives the user a convenient way to check for an overrun.

which probably makes me one of those new users. I guess the question is how to fix the situation. If I am able to pass the algorithm the elapsed time, would it still work okay?

from arduino-pid-library.

@owhite please see: #9. Then simply call:

myPID.SetSampleTime(0);

from arduino-pid-library.

Also check out my PID implementation for my flight controller: https://github.com/Lauszus/LaunchPadFlightController/blob/master/src/PID.c and the PID code for the Balanduino balancing robot: https://github.com/TKJElectronics/Balanduino/blob/master/Firmware/Balanduino/Motor.ino.

from arduino-pid-library.

@owhite please see: #9. Then simply call:

myPID.SetSampleTime(0);

This does not work! If you look at the SetSampleTime() code

void PID::SetSampleTime(int NewSampleTime)
{
   if (NewSampleTime > 0)
   {
      double ratio  = (double)NewSampleTime
                      / (double)SampleTime;
      ki *= ratio;
      kd /= ratio;
      SampleTime = (unsigned long)NewSampleTime;
   }
}

You can see that if '0' is passed in as 'NewSampleTime', the value of 'SampleTime' will not be changed! The 'if' statement needs to be changed to 'if (NewSampleTime >= 0)

Frank

from arduino-pid-library.