Source Code - PID() Function

PID Algorithm generates a control variable from the current value, and the required value. Since the aim is to keep the line always beneath the center sensor so the required value is 3 (second parameter). The first argument is the current sensor reading. The more the difference between the two greater is the control variable. This control variable is used to produce turning in the robot. When current value is close to required value is close to 0.

Arguments:

cur_value - current line position, range is from 1-5 (1= LEFT Most sensor, 5= right most)

data type: float.

req_value - desired position, since sensor 3 is the middle sensor and the aim is to keep the line below middle sensor so this value is 3.

data type: float

Return Value:

control variable, the amount of correction required. When the control variable is more than 0 that means line is towards the left, so we need to take right turn to correct the error and bring the robot back to track.

Similarly if control variable is less than 0 that means line is towards the right, so we need to take left turn to correct the error and bring the robot back to track.

Implementation

float PID(float cur_value,float req_value)
{
  float pid;
  float error;

  error = req_value - cur_value;
  pid = (pGain * error)  + (iGain * eInteg) + (dGain * (error - ePrev));

  eInteg += error;                  // integral is simply a summation over time
  ePrev = error;                    // save previous for derivative

  return pid;
}
 

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