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Need help with adc pic 16f877a

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tamer1221

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adc pic16f877a

im using mikroc to program
unsigned temp ;

void main() {
temp=0;
TRISB = 0x00;
ADCON1 = 0x8E;
TRISA = 0xFF;


while(1) {
PORTB = 0x00;
temp = ADC_read(0);
delay_ms(50);

if(temp>40)
{
PORTB=0x00;
DELAY_MS(50);
PORTB=0xff;
DELAY_MS(50) ;
}
}
}
the problem is the led keep blinking even when 0 volt is applied to an0
 

adc pic

The pic has a 10-bit A/D converter. If you are using the 5 Volt rail as a reference, 40 is not a very large voltage.

5 / 1024 = 0.0048 volts per bit
40 * 0.0048 = 0.192 volts.

You could easily have 200mV of noise on your input?
 
adc in pic16f877a using mikroc

that is the problem my input is 0.20 v
 

pic16f877a using 10bit adc program

Remember you cannot directly measure down to 0v. You really need to condition the signal first, say with a low noise op amp. Better to scale input so you measure say from 1-4 volts. You can the calibrate in software to give 0 to vmax output
 

adc in pic

as far as I remember.. there was an ADC_setup() function you should call before reading!
 

dont use adc function directly .. write program specifically how u need the output
 

use veritable resister with ground for RA0 pin and try
 

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