Afdhal Atiff Tan: Programmable Fridge Timer

Somewhere in February of 2013, my dad ask me to build him a timer for fridge, that turns on 3 times a day, i.e. 1 hour on, 7 hours off. The fridge temperature regulating mechanism failed, causing it to run entire day, consuming too much energy and money.

Get excited, I surveyed online for small PIC microcontroller. After all ordered component arrived, I kickstart the project quick. :)

I'm using cheap PIC10F220 6-pin mcu and 40A automotive relay for the project. Most of the circuit are for power supply and relay triggering.

The relay contacts are equipped with capacitive snubber for arc-suppression, enhancing relay's life.

Firmware is coded with XC8 compiller in MPLABX, running forever-loop of delays.

#include <xc.h>
#include <pic10f220.h>
#pragma config IOSCFS = 4MHZ    // Internal Oscillator Frequency Select bit (4 MHz)
#pragma config MCPU = OFF       // Master Clear Pull-up Enable bit (Pull-up disabled)
#pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled)
#pragma config CP = OFF         // Code protection bit (Code protection off)
#pragma config MCLRE = ON       // GP3/MCLR Pin Function Select bit (GP3/MCLR pin function is MCLR)
#define _XTAL_FREQ 4E6

unsigned int RAM=0;

void picInit()
{
    GPIO = 0;
    ADCON0 = 0;   
    OPTION = 0xC8;
    OSCCAL = 0x18;  //Calibrated with Rigol DS1102E on 3Feb2013
    TRISGPIO = 0;
    __delay_ms(3000); //delayed on
}

void delay1h()
{
    for(int x=0; x<3600; x++)
    {
        __delay_ms(500);
        RAM &= 0xFB;
        GPIO = RAM;
        __delay_ms(500);
        RAM |= 0x04;
        GPIO = RAM;
    }
}

void main()
{
    picInit();   
    RAM = 0xFF;   
    GPIO = RAM;

while(1)
    {
        for(int y=0; y<1; y++)  //ontime
        {
            delay1h();
        }

RAM &= 0xFC;
        GPIO = RAM;

for(int z=0; z<7; z++)   //offtime
        {
            delay1h();
        }

RAM |= 0x03;
        GPIO = RAM;
    }
}

The 3 lower GPIO used for driving the relay, the relay-status LED, and running-LED.
It comes with power-up 3 seconds delay.