Yet Another PID (YAPID) library for Arduino

Contact: Auralius Manurung, Universitas Telkom, [email protected]

Detailed documentations: https://auralius.github.io/yapid/

---

In YAPID, the discrete implementations of both the control and the filter use bilinear transformation (Tustin or trapezoidal) method. Check this page for details on the control derivation.

Implemented functions:

• float YAPID::Compute0(float set_value, float process_value)

  • This simply sends set_value as control output.
  • There is no feedback control happening here.
  • This function is useful to testing system's open-loop respose.

• float YAPID::Compute1(float set_value, float process_value)

  • D-term is computed from the filtered errors.
  • Derivative kicks will happen
  • Simple integral windup prevention with clamping technique

• float YAPID::Compute2(float set_value, float process_value)

  • D-term is computed from the filtered process values
  • No more derivative kicks
  • Simple integral windup prevention with clamping technique

• float YAPID::FOLP(float tau, float in)

  • First-order low-pass filter (time-constant filter)

• float YAPID::SOLP(float tau, float in)

  • Second-order low-pass filter (Butterworth filter)

How to use the YAPID library

Abbreviations:

• sv: set value
• pv: process value
• co: control output
• P: P-term control output
• I: I-term control output
• D: D-term control output
• Kp: proportinal gain
• Ki: integral gian
• Kd: derivative gain
• N: derivative filter coefficient

How to use:

YAPID DOES NOT measure the elapsed time every iteration. It simply uses the provided sampling time during the setup. Therefore, to guarantee control determinism, it is easier if we use a timer interrupt handler to run the control periodically. All provided examples use timer interrupts.

To use YAPID library, first, we need to include the header file:

#include "yapid.h"

Next, we create a global YAPID object and several global variables:

// Create the PID controller
float kp = 100.;  // kp
float ki = 10.0;  // ki
float kd = 1.0;   // kd
float N  = 1.0;   // derivative filter coefficient (Hz)
float Ts = 1e-3;
YAPID pid(Ts, kp, ki, kd, N);

Within the Arduino's setup() function, we define the limits for the control's output. The default limit is $0.0 \leq \text{CO} < 255.0$. Since we use a timer interrupt, we setup out timer interrupt also in this setup() function.

#define TIMER2_INTERVAL_MS 1  // 1kHz

void setup()
{
  // Setup the timer interrupt (we use NANO, timer-1, and
  // https://github.com/khoih-prog/TimerInterrupt)
  ITimer1.init();
  ITimer1.attachInterruptInterval(TIMER1_INTERVAL_MS, Timer1Handler);

  // Define the control output limits
  // Here, the output becomes PWM signals (0 to 255)
  pid.SetOutputLimits(0., 255)

  // ...
  // ...
}

Finally, in the timer interrupt function handler, we can put our PID control. The steps are:

• read the sensor (pv)
• compute the PID (co)
• apply the output to the actuator/plant
• measure the elapsed time

void Timer1Handler()
{ 
  float pv = (float)analogRead(A0) * 5.0 / 1024.0;

  float co = pid.Compute1(SV, pv);
  
  analogWrite(pwm_port, (int)co);
  
  pid.UpdateTime();
}