Strange ADC behaviour

[ruijc]

Hi guys,

i've made a simple circuit to measure the ad value from 2 channel of my 16F88 pic out to a LCD.

The strange thing is that porta.1 's values are conditioned by the results in porta.0 !

For example... this is what i get on my LCD...


Porta.1 = 5.00v lcd = 5.0
porta.0 = 5.00v lcd = 5.0

Porta.1 = 0.17v lcd = 0.17
Porta.0 = 5.00v lcd = 4.17

porta.1 = 2.54v lcd = 2.54
porta.0 = 5.00v lcd = 4.54

porta.1 = 5.00v lcd = 5.00
porta.0 = 4.58v lcd = 5.00

Here's the code:

output portb.7
low portb.7

Define osc 4

' Define LCD pins
Define LCD_DREG PORTB
Define LCD_DBIT 0
Define LCD_RSREG PORTB
Define LCD_RSBIT 4
Define LCD_EREG PORTB
Define LCD_EBIT 5
Define LCD_BITS 4

'variables
va1 var word
va2 var word
temp var word
volt var word

pause 200 'init LCD
lcdout $fe,1 'clear LCD

'Define ADCIN parameters
Define ADC_BITS 10 ' Set number of bits in result ( 8 or 10 bits )
Define ADC_CLOCK 3 ' Set clock source (3=rc)
Define ADC_SAMPLEUS 50 ' Set sampling time in uS

input porta.0
input porta.1

ADCON1 = %10000011 ' set porta analog and right justify result

loop:

ADCIN 0, va1
ADCIN 1, va2

temp = (va1 */ 500 ) >> 2
volt = (va2 */500) >>2

high portb.7

lcdout $fe,2,"VOLTAGE..",dec (volt/100),",",dec2 volt,"V"
lcdout $fe,$c0,"TEMP.....",dec (temp/100),",",dec2 volt,"V"

pause 250

Goto loop

End

Thanks

[mister_e]

In theory the comparator should already be off at POR, but for safety sake, add this line at the top of your code

CMCON=7

This kind of weirdness is usually caused by a too high external analog impedance, AND/OR a too short sampling time, or combination of. Make sure your external source is bellow the maximum recommended (<10K if my memory serves me well for this device).

You could still add some PAUSE/PAUSEUS between each ADCIN to see if it's better or worst.

I'll suggest to properly set the ANSEL register and set to digital all unused i/o as well.

BUT the main problem is in red

lcdout $fe,2,"VOLTAGE..",dec (volt/100),",",dec2 volt,"V"
lcdout $fe,$c0,"TEMP.....",dec (temp/100),",",dec2 volt,"V"

have a look at DIG modifier as well.

[ruijc]

Thanks mister_e

I guess i need glasses on this one...

lcdout $fe,2,"VOLTAGE..",dec (volt/100),",",dec2 volt,"V"
lcdout $fe,$c0,"TEMP.....",dec (temp/100),",",dec2 volt,"V"

Corrected that but still some strange behaviour...

With
porta.1 = 0.16v lcd 0.16 and porta.0=5v lcd 5

but

with porta.1 = 0.16v AND porta.0 = 0.16v lcd 0.00v on both

I'm guessing some comparator issue here...

[mister_e]

ah come on let's see what happen if i put some explanation 'round.

lcdout $fe,2,"VOLTAGE..",dec (volt/100),",",dec2 volt,"V"

GOOD! you want to display voltage, that's what you do in both DEC and DEC2 modifier.

NOW

lcdout $fe,$c0,"TEMP.....",dec (temp/100),",",dec2 volt,"V"
'
'
'

Why are you mixing temp AND VOLT......?

[ruijc]

Let me correct my last statement:

Having 2 LM35 on my breadboard

Porta.1 working fine either each one

Porta.0 showing 0.00 when conected to any one of them

Tryed a pot to get a lower voltage ( 0.16v ) like the LM35 but with the pot is working !!!
Also getting good readings from other like pulldown resistor or 5v supply !

Same code for both though

added :

pauseus 500 between each adc reading,

also

CMCON=7 on top of code

Any ideas ?

[ruijc]

sorry Mister-e...

You did not undestand my post

i was just quoting your statement...i did corrected that

this is how it is:

lcdout $fe,2,"VOLTAGE..",dec (volt/100),",",dec2 volt,"V"
lcdout $fe,$c0,"TEMP.....",dec (temp/100),",",dec2 temp,"C"



.

[mister_e]

EDIT: let me see...

[ruijc]

i get

voltage = 2.49
temp = 1.25

.

[b1arrk5]

You might also try a little pause between reading adc channels, to make certain that the internal capacitor has fully discharged between readings. Someone else just had a similar problem last week, it's posted on this forum.

Jerry.

[ruijc]

Hi guys,

some changes made but still Porta.0 is running the show

If i change the input on porta.0 it changes my "fixed" reading on porta.1

What i did :

Turned on the Vref+ and with a voltage drop through resistors i managed to get 1.6V vref in porta.3 and added this in my code:
ADCON1 = %10100011

Also added a pauseus between readings
pauseus 1000

placed on LCD the original adc reading followed by the math result
lcdout $fe,2, dec tes1, " PA1 ", dec volt, " "
lcdout $fe,$c0,dec te0," PA0 ", dec temp, " "

Acetronics,

you said that you re-wrote my code and it worked...

One question:

Have you made any changes ?

I dont know where to turn now

.

[Acetronics2]

Acetronics,

you said that you re-wrote my code and it worked...

One question:

Have you made any changes ?

.

Hi, Ruijc

I did not make any noticeable change to your " functionnal " program ( = the part that runs )

BUT ... as I told you, The config section took me ~ 50 lines.

Here is your headache : The processor config lines !!!

'*****************************************************************************
'*****************************************************************************
'09/12/2007
'
'Lecture de 2 temp avec LM35 ( ambiant  temp ... LOL ! )
'
'PIC 16F88 @ 4Mhz

'*****************************************************************************
'Config

@	__CONFIG    _CONFIG1, _CP_OFF & _CCP1_RB3 & _DEBUG_OFF & _WRT_PROTECT_OFF & _CPD_OFF & _LVP_OFF & _BODEN_OFF & _MCLR_ON & _PWRTE_ON & _WDT_ON & _INTRC_IO

@ 	__CONFIG    _CONFIG2, _IESO_OFF & _FCMEN_OFF

OSCCON 	= %01101110 'Internal RC w/ I/Os

INTCON	= 0
PIE1	= 0
PIE2	= 0
CMCON	= 7
CVRCON 	= 0

        
'*****************************************************************************
'DEFINEs
'*****************************************************************************

'OSC

DEFINE osc 4

'*****************************************************************************
'
'ADC

DEFINE ADC_BITS 10 ' Set number of bits in result ( 8 or 10 bits )

'DEFINE ADC_CLOCK 3 ' Set clock source (3=rc)

DEFINE ADC_SAMPLEUS 50 ' Set sampling time in uS

'*****************************************************************************
'
'LCD 

DEFINE LCD_DREG PORTB
DEFINE LCD_DBIT 0
DEFINE LCD_RSREG PORTB
DEFINE LCD_RSBIT 4
DEFINE LCD_EREG PORTB
DEFINE LCD_EBIT 5
DEFINE LCD_BITS 4

DEFINE LCD_COMMANDUS 2000

'*****************************************************************************
'ADC parameters

ADCON0	= %11000000 ' clock source
ADCON1 	= %10000011 ' set porta.0 and .1 analog and right justify result
ANSEL 	= %00000011 ' Porta.0 and  .1 used by ADC

'*****************************************************************************
' variables

va1 	var word
va2 	var word
temp 	var word
volt 	var word

LM351 	con 0
LM352	con 1

CLEAR

'*****************************************************************************
'I/O's

PORTA = %00000000
PORTB = %00000000

TRISA = %00000011
TRISB = %00000000

'*****************************************************************************
'PINS

LM35_1	var PORTA.0 
LM35_2	var PORTA.1 
a2		var PORTA.2 
a3		var PORTA.3 
a4		var PORTA.4 
MCLR	var PORTA.5 
a6		var PORTA.6 
a7		var PORTA.7 

DATA1	var PORTB.0
DATA2	var PORTB.1
DATA3	var PORTB.2
DATA4	var PORTB.3

R_S		var PORTB.4
E		var PORTB.5
b6		var PORTB.6
LED		var PORTB.7


'*****************************************************************************
'*****************************************************************************
'
'*****************************************************************************
'Init LCD

pause 500 'init LCD
lcdout $fe,1 'clear LCD


loop:

ADCIN LM351, va1 ' 15 °C ... 150 /5000*1024 = 30.72 ... 30 = NOT GOOD !!!
ADCIN LM352, va2

'temp = (va1 */ 500 ) >> 2
temp = (va1*125)
temp = temp.Highbyte

'volt = (va2 */500) >> 2
volt = (va2*125)
volt = volt.Highbyte

high portb.7

lcdout $fe,2,"VOLTAGE..",dec (volt/100),".",dec2 volt,"V"
lcdout $fe,$c0,"TEMP.....",dec (temp/100),".",dec2 volt,"V"

pause 250 

Goto loop

End

as you can see it ....no great change to what you did ...


IT IS FORBIDDEN TO YOU TO PASTE THAT CODE ... before having understood YOU MUST CONFIGURE the registers and ports by YOURSELF !!!

PbP cares for some ... yes, but only some "general use" ones.

Also try to show a "readable" listing where you ( mostly ! ) and others can find if you've programmed the "good" registers or not ...

And for the end ... remember to separate the "config zone" and the "working zone" ... setting registers in the "working zone" must be kept ONLY if changes have to be made while running ...


Here we are ... PbP doesn't do everything for you ...that's it

Especially read those F...manual and Datasheet !!!


Keep on ... thinking you're good at pics ... you'll become really good one day !!!

Alain