arduino-pid-autotuner

Automated PID tuning using Ziegler-Nichols/relay method.

Originally written for Arduino and compatible boards, but does not rely on the Arduino standard library.

Disclaimer

Issues have been disabled on this repository due to too many off-topic questions about PID control in general or how to use this code. This project is a simple implementation of the algorithm described here and is not guaranteed to work in every use case. If you don't know what this code is intended to do, you probably don't need to use it.

How does it work?

pidautotuner.h and pidautotuner.cpp are fully commented to explain how the algorithm works.

What PID controller does this work with?

This algorithm should work with any implementation of PID control if it is properly configured.

Example code (Arduino)

#include <pidautotuner.h>

void setup() {

    PIDAutotuner tuner = PIDAutotuner();

    // Set the target value to tune to
    // This will depend on what you are tuning. This should be set to a value within
    // the usual range of the setpoint. For low-inertia systems, values at the lower
    // end of this range usually give better results. For anything else, start with a
    // value at the middle of the range.
    tuner.setTargetInputValue(targetInputValue);

    // Set the loop interval in microseconds
    // This must be the same as the interval the PID control loop will run at
    tuner.setLoopInterval(loopInterval);

    // Set the output range
    // These are the minimum and maximum possible output values of whatever you are
    // using to control the system (Arduino analogWrite, for example, is 0-255)
    tuner.setOutputRange(0, 255);

    // Set the Ziegler-Nichols tuning mode
    // Set it to either PIDAutotuner::ZNModeBasicPID, PIDAutotuner::ZNModeLessOvershoot,
    // or PIDAutotuner::ZNModeNoOvershoot. Defaults to ZNModeNoOvershoot as it is the
    // safest option.
    tuner.setZNMode(PIDAutotuner::ZNModeBasicPID);

    // This must be called immediately before the tuning loop
    // Must be called with the current time in microseconds
    tuner.startTuningLoop(micros());

    // Run a loop until tuner.isFinished() returns true
    long microseconds;
    while (!tuner.isFinished()) {

        // This loop must run at the same speed as the PID control loop being tuned
        long prevMicroseconds = microseconds;
        microseconds = micros();

        // Get input value here (temperature, encoder position, velocity, etc)
        double input = doSomethingToGetInput();

        // Call tunePID() with the input value and current time in microseconds
        double output = tuner.tunePID(input, microseconds);

        // Set the output - tunePid() will return values within the range configured
        // by setOutputRange(). Don't change the value or the tuning results will be
        // incorrect.
        doSomethingToSetOutput(output);

        // This loop must run at the same speed as the PID control loop being tuned
        while (micros() - microseconds < loopInterval) delayMicroseconds(1);
    }

    // Turn the output off here.
    doSomethingToSetOutput(0);

    // Get PID gains - set your PID controller's gains to these
    double kp = tuner.getKp();
    double ki = tuner.getKi();
    double kd = tuner.getKd();
}

void loop() {

    // ...
}