--> Digital Voltmeter using AT89S52 and ADC0809

This project can measure DC voltages from 0 to 5v using ADC0809. The voltage is shown over the seven segment displays.
Connections:

• P1.0 to P1.7 is connected to the ABCDEFGH segments of the displays.
• P2.0 to P2.3 is connected to the Common Anodes of the displays
• P3.0 is connected to the ST pin of the ADC
• P3.1 is connected to the OE pin of the ADC
• P3.2 is connected to the EOC pin of the ADC
• P3.3 is connected to the CLK pin of the ADC
• The address lines (A,B,C) are connected to ground so that the first channel is selected.
• The Input DC voltage is connected to the IN0 of the ADC.
• P0.0 to P.07 is connected to the Data line of the ADC

Circuit Diagram:

Source code:
[code:c]#include
 
unsigned char code dispbitcode[] = {0xfe,0xfd,0xfb,0xf7,
                                  0xef,0xdf,0xbf,0x7f};
unsigned char code dispcode[] = {0x3f,0x06,0x5b,0x4f,0x66,
                               0x6d,0x7d,0x07,0x7f,0x6f,0x00};
unsigned char dispbuf[8]={10,10,10,10,0,0,0,0};
unsigned char dispcount;
unsigned char getdata;
unsigned int temp;
unsigned char i;
 
sbit ST=P3^0;
sbit OE=P3^1;
sbit EOC=P3^2;
sbit CLK=P3^3;
 
 
void main(void)
{
  ST=0;
  OE=0;
  ET0=1;
  ET1=1;
  EA=1;
  TMOD=0x12;
  TH0=216;
  TL0=216;
  TH1=(65536-4000)/256;
  TL1=(65536-4000)%256;
  TR1=1;
  TR0=1;
  ST=1;
  ST=0;
  while(1)
    {
      if(EOC==1)
        {
          OE=1;
          getdata=P0;
          OE=0;
          temp=getdata*235;
          temp=temp/128;
          i=5;
          dispbuf[0]=10;
          dispbuf[1]=10;
          dispbuf[2]=10;
          dispbuf[3]=10;
          dispbuf[4]=10;
          dispbuf[5]=0;
          dispbuf[6]=0;
          dispbuf[7]=0;
          while(temp/10)
            {
              dispbuf[i]=temp%10;
              temp=temp/10;
              i++;
            }
          dispbuf[i]=temp;         
          ST=1;
          ST=0;
        }
    }
}
 
void t0(void) interrupt 1 using 0
{
  CLK=~CLK;
}
 
void t1(void) interrupt 3 using 0
{
  TH1=(65536-4000)/256;
  TL1=(65536-4000)%256;
  P1=dispcode[dispbuf[dispcount]];
  P2=dispbitcode[dispcount];
  if(dispcount==7)
    {
      P1=P1 | 0x80;
    }
  dispcount++;
  if(dispcount==8)
    {
      dispcount=0;
    } 
}[/code]

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