PID Control Object (with questions)

Continued:
Add a method to do one iteration of PID control

PIDobj.prototype.update=function(){
  this.N++;
  var A=this.PID;
  var inp=this.Input();
  this.error=this.Setpoint-inp;
  this.integral+=this.error*this.Interval/­1000;
  if(this.integral<0)this.integral=0;
  if(this.integral>1)this.integral=1;
  this.derivative=(this.error-this.previou­s_error)*1000/this.Interval;
var b=this.out+A.Dir*(A.P*this.integral+A.I*­this.error+A.D*this.derivative);
  if(b<0)b=0;if(b>1)b=1;

 this.Output(b);
 this.out=b;
 console.log(this.N,',',this.error.toFixe­d(4),',',inp.toFixed(4),",",b.toFixed(4)­,",",this.Setpoint.toFixed(4));
 var Q = E.openFile(this.PID.Fname, "a");
 Q.write(this.N,this.error.toFixed(4),inp­.toFixed(4),b.toFixed(4),this.Setpoint.t­oFixed(4)+"\r");
 Q.close();
  this.previous_error=this.error;
};//end update

And finally some code to test it all.

function input1(){
//  console.log("in ",analogRead("A1"));
  return analogRead("A1");
}// end input;


function output1(a){
//  console.log("Out ",a);
  analogWrite('A4',a);
}//end output

function Testit(){
//A1.mode('analog');
//A4.mode('analog');
output1(0.5); //1.0
  var PID1=new PIDobj(PID,0.5,input1,output1,1000);
  input1();
  PID1.start();
}//end Testit

Testit();

For a simple test on an Espruino board I connected pin A4 to Pin A1.
Some console output:

>echo(0);
=undefined
1 , -0.0005 , 0.5005 , 0.0000 , 0.5000
2 , 0.4802 , 0.0198 , 0.1441 , 0.5000
3 , 0.3562 , 0.1438 , 0.2509 , 0.5000
4 , 0.2493 , 0.2507 , 0.3652 , 0.5000
5 , 0.1348 , 0.3652 , 0.4672 , 0.5000
6 , 0.0322 , 0.4678 , 0.5602 , 0.5000
7 , -0.0618 , 0.5618 , 0.6384 , 0.5000
8 , -0.1399 , 0.6399 , 0.6965 , 0.5000
9 , -0.1978 , 0.6978 , 0.7309 , 0.5000
10 , -0.2329 , 0.7329 , 0.7409 , 0.5000
11 , -0.2427 , 0.7427 , 0.7282 , 0.5000
12 , -0.2297 , 0.7297 , 0.7065 , 0.5000
13 , -0.2080 , 0.7080 , 0.6879 , 0.5000
14 , -0.1899 , 0.6899 , 0.6707 , 0.5000
15 , -0.1719 , 0.6719 , 0.6553 , 0.5000
16 , -0.1563 , 0.6563 , 0.6412 , 0.5000
17 , -0.1423 , 0.6423 , 0.6284 , 0.5000
18 , -0.1291 , 0.6291 , 0.6168 , 0.5000
19 , -0.1182 , 0.6182 , 0.6061 , 0.5000
20 , -0.1067 , 0.6067 , 0.5965 , 0.5000
21 , -0.0986 , 0.5986 , 0.5875 , 0.5000
22 , -0.0884 , 0.5884 , 0.5797 , 0.5000
23 , -0.0811 , 0.5811 , 0.5723 , 0.5000
24 , -0.0739 , 0.5739 , 0.5656 , 0.5000
25 , -0.0669 , 0.5669 , 0.5596 , 0.5000
26 , -0.0605 , 0.5605 , 0.5542 , 0.5000
27 , -0.0552 , 0.5552 , 0.5492 , 0.5000
28 , -0.0498 , 0.5498 , 0.5448 , 0.5000
29 , -0.0459 , 0.5459 , 0.5406 , 0.5000
30 , -0.0415 , 0.5415 , 0.5369 , 0.5000

Tuning the P, I, and D values is an art. Please consult Google.
Things to try:

1. Use an RC low-pass circuit between the output pin and the input pin. One or many stages of RC filter.
   
2. Try setting the analogWrite() to a 50 Hz frequency and the pulse width of 1ms for a zero value and 2ms for a 1 value. Connect this output to a servo and use an accelerometer as the input. Mount the accelerometer on the servo arm and have some fun tilting it back and forth. (my parts are on order).
   
3. Setup a temperature sensor and a solid state switch supplying current to a heating element to control an oven temperature.
   How to make input, output and setpoint appear to the user in Engineering units?
   
   
   

2 Attachments

• PIDobj2.js
• PID.CSV