Hi guys, I am learning how to use PID. Ultimately want to control the temperature of a small environment (box) by adjusting the speed of a fan.
This is a sample sketch to control an LED using PID, I think if I understand this sketch, I can implement it into my own project.
My question is: For the if-else structure in the second half of the sketch, it seem like the main purpose is to get new tuning values. If I want to use auto tune, it would replace the entire if-else structure?
Source: http://www.pdx.edu/nanogroup/sites/www.pdx.edu.nanogroup/files/2013_Arduino%20PID%20Lab_0.pdf (code on page 3-4, schematic page 6)
#include <PID_v1.h>
const int photores = A0; // Photo resistor input
const int pot = A1; // Potentiometer input
const int led = 9; // LED output
double lightLevel; //variable that stores the incoming light level
// Tuning parameters
float Kp=0; //Initial Proportional Gain
float Ki=10; //Initial Integral Gain
float Kd=0; //Initial Differential Gain
double Setpoint, Input, Output; //These are just variables for storing values
PID myPID(&Input, &Output, &Setpoint, Kp, Ki, Kd, DIRECT); // This sets up our PDID Loop
//Input is our PV
//Output is our u(t)
//Setpoint is our SP
const int sampleRate = 1; // Variable that determines how fast our PID loop runs
// Communication setup
const long serialPing = 500; //This determines how often we ping our loop
// Serial pingback interval in milliseconds
unsigned long now = 0; //This variable is used to keep track of time
// placehodler for current timestamp
unsigned long lastMessage = 0; //This keeps track of when our loop last spoke to serial
// last message timestamp.
void setup(){
lightLevel = analogRead(photores); //Read in light level
Input = map(lightLevel, 0, 1024, 0, 255); //Change read scale to analog out scale
Setpoint = map(analogRead(pot), 0, 1024, 0, 255); //get our setpoint from our pot
Serial.begin(9600); //Start a serial session
myPID.SetMode(AUTOMATIC); //Turn on the PID loop
myPID.SetSampleTime(sampleRate); //Sets the sample rate
Serial.println("Begin"); // Hello World!
lastMessage = millis(); // timestamp
}
void loop(){
Setpoint = map(analogRead(pot), 0, 1024, 0, 255); //Read our setpoint
lightLevel = analogRead(photores); //Get the light level
Input = map(lightLevel, 0, 900, 0, 255); //Map it to the right scale
myPID.Compute(); //Run the PID loop
analogWrite(led, Output); //Write out the output from the PID loop to our LED pin
now = millis(); //Keep track of time
if(now - lastMessage > serialPing) { //If its been long enough give us some info on serial
// this should execute less frequently
// send a message back to the mother ship
Serial.print("Setpoint = ");
Serial.print(Setpoint);
Serial.print(" Input = ");
Serial.print(Input);
Serial.print(" Output = ");
Serial.print(Output);
Serial.print("\n");
if (Serial.available() > 0) { //If we sent the program a command deal with it
for (int x = 0; x < 4; x++) {
switch (x) {
case 0:
Kp = Serial.parseFloat();
break;
case 1:
Ki = Serial.parseFloat();
break;
case 2:
Kd = Serial.parseFloat();
break;
case 3:
for (int y = Serial.available(); y == 0; y--) {
Serial.read(); //Clear out any residual junk
}
break;
}
}
Serial.print(" Kp,Ki,Kd = ");
Serial.print(Kp);
Serial.print(",");
Serial.print(Ki);
Serial.print(",");
Serial.println(Kd); //Let us know what we just received
myPID.SetTunings(Kp, Ki, Kd); //Set the PID gain constants and start running
}
lastMessage = now;
//update the time stamp.
}
}