AD problems

[Samoele]

Hello,

I use two AD channel on PIC 16F877. Until interrupt pulse measure value on channel 0 and channel 1 with 2 ms delay. On AD pins have voltage divider with resistor.(from 9V to 4,5V). Problem is similar without divider.

Major problem is:
When tied pin2 from AD channel 0 to VCC (5V) shown value 294 (2,6V in my case). Channel 1 is on GND
and then tied channel 1 to VCC (5V) value on CH0 is now 511 (4,5V in my case).
I not understand why don't must be each channel separated for correct result. Is my ADCON setting correct?

TNX,
Samo

Part of my routine is:

@ DEVICE PIC16F877, HS_OSC



DEFINE OSC 20

DEFINE LCD_DREG PORTD
DEFINE LCD_DBIT 4
DEFINE LCD_RSREG PORTC
DEFINE LCD_RSBIT 6
DEFINE LCD_EREG PORTC
DEFINE LCD_EBIT 7
DEFINE LCD_BITS 4
DEFINE LCD_LINES 4
DEFINE LCD_COMMANDUS 2000
DEFINE LCD_DATAUS 50

DEFINE ADC_BITS 10
DEFINE ADC_CLOCK_2
DEFINE ADC_SAMPLEUS 3

TRISA=%11111111
ADCON1=%10010111

T1CON=%00110100 ' Set TIMER1


ANALOG1 VAR PORTA.0 'ANALOGNI VHOD1
ANALOG2 VAR PORTA.1 'ANALOGNI VHOD2
ANALOG3 VAR PORTA.3 'ANALOGNI VHOD3
INTER VAR PORTB.0 'INTERRUPT
IZHOD2 VAR PORTA.2 'IZHOD2
IZHOD1 VAR PORTB.4 'IZHOD1
IZHOD5 VAR PORTB.1 'IZHOD5
IZHOD4 VAR PORTB.2 'IZHOD4
IZHOD3 VAR PORTB.3 'IZHOD3
IZHOD1A VAR PORTA.4 'IZHOD1A
IZHOD2A VAR PORTA.5 'IZHOD2A
SCL VAR PORTA.6 'I2C CLOCK
SDA VAR PORTA.7 'I2C DATA
TSET VAR PORTB.5 'TIPKA SET
TUP VAR PORTB.6 'TIPKA UP
TDN VAR PORTB.7 'TIPKA DOWN
LED1A VAR PORTC.4 'LED1A



MERITEV1 VAR WORD
MERITEV2 VAR WORD
MER1 VAR WORD
MER2 VAR WORD
MER2A VAR WORD
MER2B VAR WORD
MER2X VAR WORD
MER1A VAR WORD
MER1B VAR WORD
MER1X VAR WORD
MER2Y VAR WORD
MER1Y VAR WORD


LCDOUT $FE,$40,$10,$10,$08,$04,$02,$01,$01,$01 '\
LCDOUT $FE,$48,$01,$01,$01,$01,$01,$01,$01,$01 'I
LCDOUT $FE,$50,$00,$00,$00,$00,$00,$00,$00,$1F 'I

LCDOUT $FE,1


On Interrupt Goto SAMPLE ' Define interrupt handler
INTCON = $90 ' Enable INTE interrupt


MAIN: MER1=MERITEV1/112
MER1Y=MERITEV1//112
MER1X=(MER1Y*10)/112

MER2=MERITEV2/112
MER2Y=MERITEV2//112
MER2X=(MER1Y*10)/112

LCDOut $FE,2,1,0,#MER1,".",#MER1X,"V"
LCDOut $FE, $C0,1,1,2,2,#MERITEV1
LCDOut $FE, $90,1," ",1,#MER2,".",#MER2X,"V"
LCDOut $FE, $D0,1," ",1,#MERITEV2
LOW LED1A
GOTO MAIN




Disable
SAMPLE: ADCIN 0,MERITEV1
PAUSE 2
ADCIN 1,MERITEV2

HIGH LED1A


INTCON.1 = 0 ' Clear interrupt flag
Resume
Enable
GOTO MAIN
END

[mister_e]

we don't know much about your external analog source but assuming a 10K, the ADC sampling time is way too low. Use my PicMultiCalc to know the right value for your actual setup.

Here if i use 10K, the DEFINEs will be...


DEFINE ADC_BITS 10 ' ADCIN resolution (Bits)
DEFINE ADC_CLOCK 2 ' ADC clock source (Fosc/32)
DEFINE ADC_SAMPLEUS 11 ' ADC sampling time (uSec)

now...


MER1=MERITEV1/112
MER1Y=MERITEV1//112
MER1X=(MER1Y*10)/112

MER2=MERITEV2/112
MER2Y=MERITEV2//112
MER2X=(MER1Y*10)/112
to me it's suppose to be MER2Y


ADCON1=%10010111
i don't see this setting in the datasheet... for now, it make all pins to digital.

i did the test with ADCON1=%10000000
and it works.. well here ;)

[Bruce]

And, based on your analog pin assignments;


ANALOG1 VAR PORTA.0 'ANALOGNI VHOD1
ANALOG2 VAR PORTA.1 'ANALOGNI VHOD2
ANALOG3 VAR PORTA.3 'ANALOGNI VHOD3
If you change ADCON1=%10010111 to ADCON1=%10000100, that would
set RA0, RA1 and RA3 up as analog inputs to match. Assuming analog Vref
is Vdd & Vss.

[Samoele]

Thank you for your help. It is working now.

Samo