Adc 0808

[simrantogether]

Hi all,

After so much time i am using ADC0808 again in one of the tasks...


The algorithm i am following is this:

• Select an analog channel by provide bits to A, B, C.
• Activate ALE with a low-to-high pulse.
• Activate SC with a high-to-low pulse (start conversion) The conversion is begun on the falling edge of the start conversion pulse. you can use circuit like

• Monitor EOC Pin .After conversion this pin goes high.
• Activate OE with a high-to-low pulse to read data out of the ADC chip.

Please suggest why the output from ADC is not received...

Regards,

Simran..

 

[simrantogether]

C Program...

Hi,

This is the code i designed from that algorithm...

#include<reg51.h>

sbit A0 		   = P0^0;
sbit A1			   = P0^1;
sbit A2 		   = P0^2;
sbit ADC_ALE		= P0^3;
sbit ADC_OE 		= P0^4;
sbit ADC_EOC 		= P0^5;
sbit ADC_START 	       = P0^7;

void msdelay(unsigned int);

void main(void)

{

while(1)
{

P0 = 0x00; // making all the bits of ports as 0

A0 = 1;
A1 = 1;
A2 = 1;	// Selecting input channel 7 by putting A1 , A2 and A3 = 1

ADC_ALE = 0;

msdelay(50);

ADC_ALE =1;		// this address of analog channel is latched with rising edge of ALE

msdelay(50);

ADC_START = 1;

msdelay(50);

ADC_START = 0;  // falling edge of ADC_START atarts the conversion of ADC


msdelay(50);	

	if(ADC_EOC = 1)
	{

	ADC_OE = 1;

	msdelay(50);

	ADC_OE = 0;

	msdelay(50);
	}

}
}





//----------------------------- Delay Routine ---------------------


void msdelay(unsigned int i)
{

unsigned int j,k;

 for(j=1; j<=i;j++)
 {
 	for(k=1;k<=1275;k++)
 	{
 	}
 	
 }

}

 

[simrantogether]

If anyone...

Hi,

If anyone has algorithm for ADC 0808 interfacing with a micro controller ...

please tell...

Or,

Please check my upper algorithm...

Regards,

Simran..

 

[Pommie]

Your code looks fine, however, you don't appear to have the data lines connected to your processor. When you set OE high, the converted value appears on D0-D7 and you need to connect them to a port and read them.

Mike.

 

[simrantogether]

Well...

Your code looks fine, however, you don't appear to have the data lines connected to your processor. When you set OE high, the converted value appears on D0-D7 and you need to connect them to a port and read them.

Mike.

Actually i interfaced the output of ADC with the LED's ...

Regards,

Simran..

 

[Pommie]

I don't think the outputs from the ADC0808 are able to directly drive LEDs.

Mike.

 

[simrantogether]

Yes...

Hi,

Yes they can...

because i used uln2803 between ADC and LED's...

Problem i find is with Code i feel...

Please check the algorithm...

Regards,

Simran..

 

[Pommie]

You are not waiting for the conversion to complete.

Try,

void main(void){
    while(1){    
        P0 = 0x00;         // making all the bits of ports as 0    
        A0 = 1;
        A1 = 1;
        A2 = 1;	           // Selecting input channel 7 by putting A1 , A2 and A3 = 1    
        ADC_ALE = 0;    
        msdelay(50);    
        ADC_ALE =1;        // this address of analog channel is latched with rising edge of ALE    
        msdelay(50);    
        ADC_START = 1;    
        msdelay(50);    
        ADC_START = 0;      // falling edge of ADC_START atarts the conversion of ADC    
        msdelay(50);	
        while(ADC_EOC!=1);  //wait for conversion to end    
        ADC_OE = 1;
        msdelay(500);       //allow time for LEDs to be viewed.
        ADC_OE = 0;
    }
}

Mike.

 

[simrantogether]

You are not waiting for the conversion to complete.

Try ....

Mike.

Thanks...

Regards,

Simran..