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jumpy adc value

 
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PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sun Jan 24, 2010 1:32 pm     Reply with quote
Connect the center tap of a 5K trimpot to pin A0 on your PIC and try
a simple program like this one. The top pin of the trimpot should go to
+5v and the bottom pin to Ground.
Code:

#include <16F877A.H>
#device adc=10
#fuses HS, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)

//============================
void main()
{
int16 adc_value;

setup_adc_ports(AN0);
setup_adc(ADC_CLOCK_DIV_32);
set_adc_channel(0);
delay_us(20);

while(1)
  {
   adc_value = read_adc();
   printf("%lu \n\r", adc_value);
   delay_ms(500);
  }
}
 

This program will display the A/D result on a serial terminal window
on your PC.
max23
Guest
PostPosted: Sun Jan 24, 2010 7:50 pm     Reply with quote
i need serial cable to connect the pic to pc right?
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sun Jan 24, 2010 8:13 pm     Reply with quote
Yes, and your board must have an RS232 interface chip, such as a
MAX232, etc. Also, your PC must have a COM port connector on the back.
Guest
PostPosted: Sun Jan 24, 2010 9:30 pm     Reply with quote
What is your input source? Does your input pin require a pullup resistor? Does your input source require a buffering capacitor? If your voltage source is jumpy, that would be the first thing to fix. If you're using a DC power supply, try replacing it with either batteries, or a different power supply. Your ADC is constantly figuring the difference between ground (0V) and VREF (+V). If your voltage source, or VREF are jumpy, your result will also be.
max23
Guest
PostPosted: Mon Jan 25, 2010 1:05 am     Reply with quote
Anonymous wrote:
Does your input pin require a pullup resistor? Does your input source require a buffering capacitor?


how do i know this?
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