Interfacing ADC0808 with Serial port (RS232) using interrupt clock from 8051 microcontroller (AT89C51)- (Part 27/45)

In many applications data collected from multiple sensors is transmitted to PC for display or further analysis. The conversion of data from analog to digital form is done using an ADC. The digital data from the ADC is transferred to the computer using serial port. This circuit demonstrates the principle and operation of interfacing an ADC0808 with serial port of PC using the microcontroller AT89C51. The circuit is divided into three parts: ADC, controller and serial port. This circuit can be used as an intermediate circuit in many applications.

ADC0808 which is an 8-bit resolution ADC has eight input channels i.e., it can take a maximum of eight analog inputs. The circuit uses the first analog input pin to take the analog input signals from the preset.

To provide clock input to the ADC, Timer0 is used in interrupt enabled mode to generate a clock of frequency 500 KHz. To enable the Timer0 in interrupt enable mode, the register IE is loaded with the value 0x82. Every time the timer completes the counting, pin P1.2 toggles its state. (Refer interfacing ADC0808 using clock from AT89C51).

The output pins of ADC are connected to the port P0 of the controller. The pin10 of the ADC is connected to pin8 (P1.7) of the controller for clock input. ALE, pin 22 of the ADC is connected to pin 1 (P1.0) of controller. OE, pin9 of the ADC is connected to pin 4 (P1.3) of controller. SC, pin6 of the ADC is connected to pin 2 (P1.1) of the controller. EOC, pin7 is connected to pin 3 (P1.2) of controller. Selector pins A (25), B (24) and C (24) of ADC are connected to the pins 4, 5 and 6 of the controller respectively.

The port P0 is continuously scanned and the output of the ADC is transmitted via serial port. The value of the port P0 is loaded in the SBUF register and sent via TxD (pin11) of the controller. Hyper Terminal shows character corresponding to the ASCII values 0-255 (Refer serial port interfacing with AT89C51 for hyper terminal settings).

Project Source Code

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// Program to read ADC 0808. The output pins are connected to serial port. Controller interrupt is used to generate the clock for driving the ADC 0808.
#include<reg51.h>
sbit ale=P1^0;    //address latch enable
sbit oe=P1^3;    //output enable
sbit sc=P1^1;    //start conversion
sbit eoc=P1^2;    //end of conversion
sbit clk=P1^7;    // clock

sbit ADD_A=P1^4;   // Address pins for selecting input channels.
sbit ADD_B=P1^5;
sbit ADD_C=P1^6;
sfr input_port=0x80;//P0 port
void transmit()    //serial port transmission
{
SBUF=input_port;
while(TI==0);
TI=0;
}
void timer0() interrupt 1             // Function to generate clock of frequency 500KHZ using Timer 0 interrupt.
{
   clk=~clk;
  }

void delay(unsigned int count)     // Function to provide time delay in msec.
{
int i,j;
for(i=0;i<count;i++)
for(j=0;j<1275;j++);
}

void main()
{
eoc=1;
input_port=0xFF;
  ale=0;
  oe=0;
  sc=0;
TMOD=0x22;   //timer0 setting for generating clock of 500KHz using interrupt enable mode.
TH0=0xFD;
IE=0x82;
TR0=1;

TH1=0xFD;  //timer1 setting for serial communication
SCON=0x50;
TR1=1;


while(1)
{
ADD_C=0;    // Selecting input channel 2 using address lines
ADD_B=0;
ADD_A=1;
delay(2);
ale=1;
delay(2);
sc=1;
delay(1);
ale=0;
delay(1);
sc=0;

  while(eoc==1);
while(eoc==0);
oe=1;
transmit();
delay(2);
oe=0;


  }

}


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