ADC problem for PIC16F877A.. How to average analog inputs for a more accurate output

[Thunderhorse312]

Hi! i am writing a program for a digital weighing scale and i want to know how do i average my input voltages from an analog port (i.e. A0) because my source voltage is not a constant input. Thus, my output values would have a large deviation without first averaging the inputs..

here is my code for the program.:

#include <htc.h>
#include <pic16f877a.h>
#include "delay.c"
#define _XTAL_FREQ 20000000

unsigned int ADCRead(unsigned char channel)
{
	unsigned char l_byte, h_byte;		//Variables in exchange for ADRESL and ADRESH
	unsigned int ADR;					//stores the Analog to Digital input value

	ADCON0 = 0x81;						//sets what channel to be used for analog input
	DelayUs(50);						//acquistion time delay
	GO_DONE = 1;						//start the A/D conversion

	while(GO_DONE == 1); 				//wait for the bit to be cleared

	l_byte = ADRESL;
	h_byte = ADRESH;

	ADR = (h_byte << 8)|l_byte;			//shift ADRESH 8 places to the left and be ORed with ADRESL

	return ADR;

}

	void main(void)
		{
			#define Weight25 8
			#define Weight30 9
			#define Weight31 10
			#define Weight35 11	
			#define Weight36 12
			#define Weight40 13
			#define Weight41 14
			#define Weight46 15
			#define Weight47 16
			#define Weight52 17
			#define Weight53 18
			#define Weight58 19
			#define Weight59 20
			#define Weight64 21
		    #define Weight65 22
			#define Weight70 23
			#define Weight71 24
			#define Weight76 25
			#define Weight77 26
			#define Weight82 27
			#define Weight83 28
			#define Weight88 29
			#define Weight89 30
			#define Weight94 32
			#define Weight95 33
			#define Weight100 34
			unsigned int Ch0;

			PORTD = 0;
			TRISD = 0;
			PORTB = 0;
			TRISB = 0;

			ADCON0 = 0x81;
			ADCON1 = 0xCD;	
			
		while (1)
				{
					Ch0 = ADCRead(0);		//Read from channel 0
					
					if (Ch0 >= Weight25)
					{
						if (Ch0 < Weight30)
							{		
								RB0 = 1; 
							}
							else
								{
								RB0 = 0;
								}
					
					}
					else
					{
								RB0 = 0;
					}		
					
					

					if (Ch0 > Weight31)				//weight 31 - 35
					{
						if (Ch0 < Weight35)
							{		
								RB1 = 1; 
							}
							
							else
								{
								RB1 = 0;
					}
					else
					{
								RB1 = 0;
					}		
					

					if (Ch0 > Weight36)					//weight 36 - 40
					{
						if (Ch0 < Weight40)
							{		
								RB2 = 1; 
							}
							
							else
								{
								RB2 = 0;
								}
					}
					else
					{
								RB2 = 0;
					}	

					
					if (Ch0 > Weight41)					//weight 41 - 46
					{
						if (Ch0 < Weight46)
							{		
								RB3 = 1; 
							}
							
					
					}
					else
					{
								RB3 = 0;
					}			
						

					if (Ch0 > Weight47)					//weight 47 - 52
					{
						if (Ch0 < Weight52)
							{		
								RB4 = 1; 
							}
							
					
					}
					else
					{
								RB4 = 0;
					}			


						if (Ch0 > Weight53)					//weight 53 - 58
					{
						if (Ch0 < Weight58)
							{		
								RB5 = 1; 
							}
							
					
					}
					else
					{
								RB5 = 0;
					}			


						if (Ch0 > Weight59)					//weight 59 - 64
					{
						if (Ch0 < Weight64)
							{		
								RB6 = 1; 
							}
							
					
					}
					else
					{
								RB6 = 0;
					}			


						if (Ch0 > Weight65)					//weight 59 - 64
					{
						if (Ch0 < Weight70)
							{		
								RD0 = 1; 
							}
							
					
					}
					else
					{
								RD0 = 0;
					}			

				

						if (Ch0 > Weight71)					//weight 59 - 64
					{
						if (Ch0 < Weight76)
							{		
								RD1 = 1; 
							}
							
					
					}
					else
					{
								RD1 = 0;
					}			
					















		
}

}


I'd like to get maybe 5 to 10 samples before getting an output.. how or what code can i use to make that sampling possible.. Also, is it possible for the ADC or is there any way that the ADC could read ADC values having decimal points. All i know is that the ADC for PIC 16F877A can read ADC values ranging form 0 to 1023 and no decimal points. Please help! thanks a lot!

 

[ste2006]

Use a For loop to scan the input say 16 times, then say sum the values and finally divide by 16 and place the value in the variable,

Something like:

for (i=0;i<16;i++)               // ADC Sampling Channel 0
       {
           SelChanConvADC(ADC_CH0);
           while(BusyADC());
           Ch0Result += ReadADC();
       }
       Ch0Result /=16;

A snippet of code from a program i am currently working on,

Obviously this requires that you include the ADC.h library,

Hope this helps

 

[Thunderhorse312]

Ahhh i see.. thanks! i was also leaning towards using the for loop in implementing sampling.. thanks again!

 

[ste2006]

no probs

glad to be of help

---------- Post added at 16:22 ---------- Previous post was at 16:22 ----------

no probs

glad to be of help