Mini HVAC

A small-scale HVAC system utilizing a closed-loop feedback PID controller that can maintain a set-point temperature within the box.

Dec 8, 2017

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pid

hvac

Components and supplies

Arduino Uno Rev3

Arduino Motor Shield Rev3

Antec 140mm PC Fan

75 Watt Desk Lamp

MCP9808 High Accuracy I2C Temperature Sensor Breakout Board

Project description

Code

Mini HVAC PID Control

arduino

PID control

1#include <AFMotor.h>
2#include <Wire.h>
3#include "Adafruit_MCP9808.h"
4
5Adafruit_MCP9808  tempsensor = Adafruit_MCP9808();
6AF_DCMotor fan(2);
7
8unsigned long currMillis;
9unsigned  long prevMillis = 0;
10double kp = 410;
11double ki = 2*kp/20; 
12double kd =  kp*20/8;
13double dt = 0.01;          // Specify sample time in seconds (fixed)
14double  dtmillis = dt*1000;  // Sample time in milliseconds
15int setpoint;
16float input;
17float  Output;
18float err;
19float pTerm;
20int IntThresh;
21float integrated_err;
22float  dTerm;
23float iTerm;
24float last_err;
25
26
27void setup(){
28  Serial.begin(9600);
29  
30  if (!tempsensor.begin()) {
31    Serial.println("Couldn't find MCP9808!");
32    while (1);
33  }
34  fan.run(RELEASE);
35  fan.setSpeed(0);
36}
37
38void  loop(){
39setpoint = 30;               // Specified by user, r(t)
40  float c  = tempsensor.readTempC();
41  Serial.print("Temp: "); 
42  Serial.println(c);  Serial.println("*C\	");
43input = (c);                 // Read by your sensor,  y(t) ... analogRead(...)
44err = (input - setpoint);    // Compute Error, e(t)  = r(t) - y(t)
45delay(200);
46// ====================== Compute Proportional term:  ========================
47pTerm = kp * (err);                 
48// ======================  Compute Integral term: ===========================
49IntThresh = .3;                      //  Set value for max intergral term
50if (abs(err) > IntThresh)            // Crude  way to prevent integrator 'windup'
51{                                    
52    integrated_err += err;           // Accumulate the error integral
53}
54else  
55{
56    integrated_err = 0;              // Zero it if out of bounds 
57}
58iTerm  = ki * integrated_err;         // Compute actual Integral term
59// ======================  Compute Derivative term: ===========================
60dTerm = kd * (err - last_err)*dt;  
61// ====================== Compute PID control command, u(t): =================
62Output  = constrain(pTerm + iTerm + dTerm, 0, 255);       
63fan.run(FORWARD);
64fan.setSpeed(Output);    // Use u(t) to drive the plant, i.e. analogWrite(Output), motor.run(Output),  etc...
65
66last_err = err;      // Set last_err to err for next time through  loop
67

#include <AFMotor.h>
#include <Wire.h>
#include "Adafruit_MCP9808.h"

Adafruit_MCP9808  tempsensor = Adafruit_MCP9808();
AF_DCMotor fan(2);

unsigned long currMillis;
unsigned  long prevMillis = 0;
double kp = 410;
double ki = 2*kp/20; 
double kd =  kp*20/8;
double dt = 0.01;          // Specify sample time in seconds (fixed)
double  dtmillis = dt*1000;  // Sample time in milliseconds
int setpoint;
float input;
float  Output;
float err;
float pTerm;
int IntThresh;
float integrated_err;
float  dTerm;
float iTerm;
float last_err;


void setup(){
  Serial.begin(9600);
  
  if (!tempsensor.begin()) {
    Serial.println("Couldn't find MCP9808!");
    while (1);
  }
  fan.run(RELEASE);
  fan.setSpeed(0);
}

void  loop(){
setpoint = 30;               // Specified by user, r(t)
  float c  = tempsensor.readTempC();
  Serial.print("Temp: "); 
  Serial.println(c);  Serial.println("*C\	");
input = (c);                 // Read by your sensor,  y(t) ... analogRead(...)
err = (input - setpoint);    // Compute Error, e(t)  = r(t) - y(t)
delay(200);
// ====================== Compute Proportional term:  ========================
pTerm = kp * (err);                 
// ======================  Compute Integral term: ===========================
IntThresh = .3;                      //  Set value for max intergral term
if (abs(err) > IntThresh)            // Crude  way to prevent integrator 'windup'
{                                    
    integrated_err += err;           // Accumulate the error integral
}
else  
{
    integrated_err = 0;              // Zero it if out of bounds 
}
iTerm  = ki * integrated_err;         // Compute actual Integral term
// ======================  Compute Derivative term: ===========================
dTerm = kd * (err - last_err)*dt;  
// ====================== Compute PID control command, u(t): =================
Output  = constrain(pTerm + iTerm + dTerm, 0, 255);       
fan.run(FORWARD);
fan.setSpeed(Output);    // Use u(t) to drive the plant, i.e. analogWrite(Output), motor.run(Output),  etc...

last_err = err;      // Set last_err to err for next time through  loop

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