The finished controller

GitHub and KC Ver. 1.01

I started a GitHub repository for my source code.

Code complete Version 1.00

After 7 alpha and 23 beta revisions, here's version 1.0 of the code. It's amazingly simple.

/*
Kegerator Thermostat Version 1.0

The circuit:
* LCD RS pin to digital pin 12
* LCD Enable pin to digital pin 11
* LCD D4 pin to digital pin 5
* LCD D5 pin to digital pin 4
* LCD D6 pin to digital pin 3
* LCD D7 pin to digital pin 2
* LCD pin 1 to ground
* LCD pin 2 to +5v
* LCD pin 3 to 4.7K ohm res to ground

* LM-34 Vout pin to Analog 0

* Button up to digital pin 7
* Button down to digital pin 8

* Relay on digital pin 13

*/

// include the library code:
#include

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

// set pin numbers:
const int relay = 13; // the number of the relay pin
const int buttonUpPin = 8; // the number of the Temp Up pin
const int buttonDnPin = 7; // the number of the Temp Down pin
const int tempPin = 0; // analog temp sensor pin
// set wait values
const int maxOffWait = 50000; // How many ms to wait to turn off
const int maxOnWait = 50000; // How many ms to wait to turn on


// variables:
int setTemp = 50; // variable storing the Set temp
int currTemp = 0; // variable storing the actual, current temp
int tempTemp = 0; // temporary temp
int buttonUpState = 0; // variable for reading the pushbutton status
int buttonDnState = 0; // variable for reading the pushbutton status
int tempIn = 0; // get temperature variable
int flagOff = 0; // flag for off delay loop
int flagOn = 0; // flag for on delay loop


void setup() {
// set up the LCD's number of rows and columns:
lcd.begin(16, 2);
// initialize the pushbutton pins as input:
pinMode(relay, OUTPUT);
digitalWrite(relay, HIGH);
pinMode(buttonUpPin, INPUT);
pinMode(buttonDnPin, INPUT);
lcd.setCursor(0, 0);
lcd.print(" Key Largo");
lcd.setCursor(0, 1);
lcd.print(" Brewery");
delay(500);
lcd.setCursor(0, 1);
lcd.print(" ");
}

void loop() {
// Print header line of output
lcd.setCursor(0, 0);
lcd.print(" Current | Set ");

// set the cursor to column 0, line 1
// (note: line 1 is the second row, since counting begins with 0):
lcd.setCursor(3, 1);
lcd.print(currTemp);
lcd.print("F ");
lcd.setCursor(9, 1);
lcd.print("|");
lcd.setCursor(11, 1);

// Check buttons for set temp
buttonUpState = digitalRead(buttonUpPin);
if (buttonUpState == HIGH) {
// add 1 to setTemp
setTemp++;
delay(250);
}
buttonDnState = digitalRead(buttonDnPin);
if (buttonDnState == HIGH) {
// subtr 1 from setTemp
setTemp--;
delay(250);
}
lcd.print(setTemp);
lcd.print("F ");

//Get the temp
tempIn = analogRead(tempPin)/8.0;
currTemp = (tempIn * 9)/ 5 + 32; // converts to fahrenheit
tempTemp = setTemp-1;

//Relay switch off logic (Anti-thrashing)
if ((tempTemp > currTemp)&&(flagOff == 0)) {
flagOff = 1;
}
if ((flagOff != 0)&&(flagOff <= maxOffWait)){
++flagOff;
}
if (flagOff >= maxOffWait){
// turn on relay
lcd.setCursor(15, 1);
lcd.print("-");
digitalWrite(relay, LOW);
flagOff = 0;
}

//Relay switch on logic (Anti-thrashing)
if ((setTemp < flagon ="="">
flagOn = 1;
}
if ((flagOn != 0)&&(flagOn <= maxOnWait)){
++flagOn;
}
if (flagOn >= maxOnWait){
// turn off relay
lcd.setCursor(15, 1);
lcd.print("+");
digitalWrite(relay, HIGH);
flagOn = 0;
}
}

All night test - Complete!

I finally got the thermostat working. I added a delay to the relay loop that makes it wait ~ 3 minutes before shutting off the relay and ~ 3 minutes before turning on the relay.

This keeps the relay/freezer from thrashing (turning on and off rapidly) when the temperature is on the cusp. I ran it all night with the set temp at 50° when I got up this morning the current temp was 48° FTW!

I’m going to lengthen the delay a little bit and add 1° to the upward set temp so it stays off longer on the temperature rise and gives a bigger compressor rest zone between runs.

Pictures and source code to follow.

IT'S DONE! -- Sort of...

The boarduino came Saturday. It took me about 10 minutes to assemble with these instructions: http://www.ladyada.net/make/boarduino/solder.html

I uncharacteristically did not take pictures. The above instructions illustrate the process better than I could.

I soldered all the connections to the peripherals and added connections to the high voltage box. I put it all together, updated the programming and plugged it it. It was a complete success... until... it cooled down to the set temp and began thrashing. The temp flickered back and forth between 51 degrees and 49 degrees about twice a second. The relay was clicking back and forth like a buzzer.

I pulled it out of service and I am working on a way to delay the cycling. My goal is to make it stay on for an extra 10 minutes to allow the temperature to "latch" and stay off on the way up for the same reason.

Waiting on parts

I ordered a "brain" for my controller. I'm getting a boarduino http://www.hvwtech.com/products_view.asp?ProductID=661 from solarobotics.
This will let me permanently solder the *duino in place. Once it arrives, I'll be minutes from being done.

High Voltage; Done & Tested

I finished wiring and mounting all the little bits in the enclosure. Testing everything was nerve-wracking.

First the Power supply. No smoke. No fire.

Then the relay board (Which I finally got working when I realized the transistor in my opto-isolator wasn't powerful enough to trip the relay. Upgrade that and Viola!). No smoke. No fire.

Then came the "All the Marbles" test. The power outlet. Plugged in a light. Tripped the relay. No smoke! No fire! Light's on!

Very exciting!