Long Delay Timer Circuit for Refrigerators(Old Types)

July 26, 2015

/ * My refrigerator does not have an automatic temperature cut-off system. So i made a long delay cut 0ff timer using 89c2051 micro controller . Here i am going to explain how it is made. */

Calculation:

Crystal frequency Used in circuit = 12Mhz
Frequency for 1 Machine cycle = 12/12 Mhz ie = 1Mhz
ie Time period for 1 Machine cycle = 1Micro seconds

Now

Calculate for 50 Milli Seconds = (50x10^-3) / (1x 10^ -6) = 50000

We program Timer O in Mode1 (16 bit)
ie maximum value is FFFF (H), or 65535 (10)

65535 - 50000 = 15535
Equivalent HEX value for Decimal 15535 = 3CAF

So in program :

TL0 = AF
TH0 = 3C

This will generate for 50 Milli Seconds, we need to calculate for 2 hours and Half an hours

Now Moving to the Program:

/ **********************************************************************/
#include<AT89x051.h>
int i,j;
     void delay1()
    //Delay for 2 hours
{
     TMOD=0x01;    //starting 16bit timer
       for (i=0;i<=380;i++)
           {
              for(j=0;j<=380;j++)
                {
    TL0=0xAF;
    TH0=0x3C;
      TR0=1;
while(TF0==0);
     TR0=0;
    TF0=0;
        }
    }
}

    void delay2()    // Delay for Half an Hour
{
     TMOD=0x01;
         for (j=0;j<=144;j++)
            {
          for(i=0;i<=144;i++)
          {
       TL0=0XAF;
       TH0=0x3C;
       TR0=1;
while(TF0==0);
       TR0=0;
       TF0=0;
        }
    }
}
       void main()
{
       P1=0;       // PORT1 = 0
       P3=0;      // PORT3 = 0
while(1)
    {
         P1_7 =1;        // PIN P1.7 High (PHASE )
         P1_6 =1;        // PIN P1.6 High (NEUTRAL )
         P1_5 =1;        // PIN P1.5 High (LED)
delay1();
        P1_7 =0;        // PIN 1.7 Low (PHASE)
        P1_6 =0;        // PIN 1.6 Low (NEUTRAL)
        P1_5 =0;        // PIN 1.6 Low (LED)
delay2();
    }
}
/ **********************************************************************/

Now going in to the circuit :

The circuit consists of two sections
1) Micro controller section
2) Relay Section

Circuit: