PID Library
/********************************************************
PID RelayOutput Example
Same as basic example, except that this time, the output
is going to a digital pin which (we presume) is controlling
a relay. The pid is designed to output an analog value,
but the relay can only be On/Off.
To connect them together we use "time proportioning
control" Tt's essentially a really slow version of PWM.
First we decide on a window size (5000mS say.) We then
set the pid to adjust its output between 0 and that window
size. Lastly, we add some logic that translates the PID
output into "Relay On Time" with the remainder of the
window being "Relay Off Time"
********************************************************/
#include <PID_v1.h>
#define RelayPin 6
//Define Variables we'll be connecting to
double Setpoint, Input, Output;
//Specify the links and initial tuning parameters
PID myPID(&Input, &Output, &Setpoint, 2, 5, 1, DIRECT);
int WindowSize = 5000;
unsigned long windowStartTime;
void setup()
{
pinMode(RelayPin, OUTPUT);
windowStartTime = millis();
//initialize the variables we're linked to
Setpoint = 100;
//tell the PID to range between 0 and the full window size
myPID.SetOutputLimits(0, WindowSize);
//turn the PID on
myPID.SetMode(AUTOMATIC);
}
void loop()
{
Input = analogRead(0);
myPID.Compute();
/************************************************
turn the output pin on/off based on pid output
************************************************/
unsigned long now = millis();
if (now - windowStartTime > WindowSize)
{ //time to shift the Relay Window
windowStartTime += WindowSize;
}
if (Output > now - windowStartTime) digitalWrite(RelayPin, HIGH);
else digitalWrite(RelayPin, LOW);
}