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pid.js
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pid.js
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// based on implementation by Tim Wescott
// https://www.wescottdesign.com/articles/pid/pidWithoutAPhd.pdf
const WINDUP_GUARD_GAIN = 100.0
var targetTemp;
var iState = 0;
var lastTemp = 0;
var pgain, igain, dgain;
var windupGaurd;
// with this setup, you pass the addresses for the PID algorithm to use to
// for storing the gain settings. This way wastes 6 bytes to store the addresses,
// but its nice because you can keep all the EEPROM address allocaton in once place.
function PID(_targetTemp, _p, _i, _d) {
targetTemp = _targetTemp;
pgain = _p
igain = _i
dgain = _d
// windup guard values are relative to the current iGain
windupGaurd = WINDUP_GUARD_GAIN / igain;
}
function getP() {
return pgain;
}
function getI() {
return igain;
}
function getD() {
return dgain;
}
function setP(p) {
pgain = p;
}
function setI(i) {
igain = i;
windupGaurd = WINDUP_GUARD_GAIN / igain;
}
function setD(d) {
dgain = d;
}
// to prevent iTerm from getting huge we use a "windup guard"
// (this happens when the machine is first turned on and
// it cant help be cold despite its best efforts)
function windupGaurdLimit(value) {
if (value > windupGaurd)
return windupGaurd;
else if (value < -windupGaurd)
return -windupGaurd;
return value;
}
function updatePID(curTemp) {
var error = targetTemp - curTemp; // how far off are we
// pTerm is the view from now
// pgain shows how much we care about error in this instant
var pTerm = pgain * error;
iState += error; // accumulated error
iState = windupGaurdLimit(iState);
var iTerm = igain * iState;
// dTerm - the difference between the temperature now and our last reading,
// shows the "speed" or how quickly the temp is changing. (aka. Differential)
var dTerm = dgain * (curTemp - lastTemp);
lastTemp = curTemp;
return pTerm + iTerm - dTerm;
}