Stable ADC readings

[Bruce]

Just include an RC filter on the A/D input, and put the PIC to sleep just before enabling the A/D conversion. This returns very stable readings in most applications with a stable power supply or Vref.

[fratello]

Nice subject !
I use a similar code for reading the over-current of one DC motor :

check:           
 vt  =0
 vs  =0
 grup=0
 cnt =0
 pause 50					
 for cnt = 1 to 10
 	adcin 3, adval
 	vt=adval * 5000
 	vt=div32 1023
 	grup=vt+grup
 	pause 5
 next cnt
 vs=grup / 10
      if (vs > checkin) or (T1Count > 50) then 		   
  	     	gpio.0=0
           	gpio.5=0
      endif

If the averge of 10 readings it's bigger than checkin value (or time exceed 5 seconds) then gpio.0 and gpio.5 goes low.
It's one good ideea to use ADCON instead ADCIN ? How to do this and keeping average of 10 readings ?

[fratello]

It's this correct ?
In header of code I add :

    ADCON0 = %10001101      ' ADC input on GPIO.4/AN3/pin3 (page 41)
                            ' MSB 1 = Right Justify                   "1"    
                            '     0 = Vdd as voltage reference        "0"
                            '     0 = n/a                             "00"
                            '     0 = n/a
                            '     1 = select channel 03 (bit 2 of 2)  "11"
                            '     1 = select channel 03 (bit 1 of 2)
                            '     0 = conversion status (see routine) "0"
                            ' LSB 1 = A/D converter module is on      "1"

And I modify the "check" subroutine like that :

check:           
 vt  =0
 vs  =0
 grup=0
 cnt =0
 pause 50			
 for cnt = 1 to 10
      ADCON0.1 = 1
      NOT_DONE:
		if ADCON0.1 = 1 THEN NOT_DONE
            Pause 10
            adval.highbyte = ADRESH
            adval.lowbyte = ADRESL
 PAUSE 10
 	vt=adval * 5000
 	vt=div32 1023
 	grup=vt+grup
 PAUSE 10
 next cnt
 vs=grup / 10
      if (vs > checkin) or (T1Count > 50) then 		   
  	     	gpio.0=0
           	gpio.5=0
      endif

The hardware it's in picture.
Thanks !

[fratello]

I've tested the code ; it's OK.

[HankMcSpank]

I've used ADCIN pretty much from day one, but I noticed I was getting some *very* jittery readings (255,243,246,255,243,246 etc)...I couldn't get to the bottom of it (spent a good while trying the usual stuff), I'd forgot about this thread but thankfully foiund it with Google)

It's the first time I've used the manual ADC method......but I'm pleased to also report my ADC readings are now solid as a rock.

Just for the record, here's what I used on my 12lf1822 (I'm only using 8 dits ADC)...

ADCON0 = %00000100     ' select ch1 (AN1 Pin 6)
ADCON1 = %00000000     'set ADC +ve reference to VCC 
' 
main:
gosub Do_ADC
pause 100
hserout [DEC ADC_RESULT,13,10]
goto main
' 
'ADC sub routine...
Do_ADC:
PAUSEUS 50              ' Wait for A/D channel acquisition time
ADCON0.1 = 1           ' Start conversion
WHILE ADCON0.1       ' Wait for it to complete
WEND
ADC_Result = ADRESH
return

Many thanks to you all on this thread...I shall never go back to the ADCIN method!

[HankMcSpank]

I wish the edit feature was open longer - I forgot to turn the ADC on above, sohere's the correction....

ADCON0 = %00000101     ' select chan1 (AN1 Pin 6), turn ADC On Bit 0

[mazoul72]

Hello,
i made this to programm ADC

bmf_comm1 VAR PORTB.0
bmf_comm2 VAR PORTB.1
'Variables
bmfsD VAR WORD
bmfs1D VAR WORD
iled var byte
blink1 var byte 'pour clignotement 1ère led
blink2 var byte 'pour clignotement 2ème led
'configuration du port pour lire l'entrée analogique
TRISA = %00000011 ' RA0 et RA1 en entrée
TRISB = %11111100 ' RB0 et RB1 en sortie
ADCON1 = $10000010 'RA0 à RA3

test_depart:
Low bmf_comm1
Low bmf_comm2
High bmf_comm1
high bmf_comm2
pause 2000
goto mainloop
'lecture de la valeur
getad:
PAUSEUS 50 ' Wait for A/D channel acquisition time
ADCON0.2 = 1 ' Start conversion
WHILE ADCON0.2 ' Wait for it to complete
WEND
Return

' Subroutine to get pot x value
getx:
ADCON0 = $41 ' Set A/D to Fosc/8, Channel 0, On
Gosub getad
bmfsD = ADRESL + (ADRESH*256)
Return

' Subroutine to get pot y value
gety:
ADCON0 = $49 ' Set A/D to Fosc/8, Channel 1, On
Gosub getad
bmfs1D = (ADRESH*256) + ADRESL
Return
val_leds:
low bmfs_comm1
low bmfs_comm2
gosub getx
gosub gety

if (bmfsD > 1000) Then Goto val_leds
if (bmfsD > 750) Then Goto boucle_led
if (bmfsD > 500) Then Goto boucle1_led
if (bmfsD > 250) Then Goto boucle2_led

High bmf_comm1
High bmf_comm2
pause 1500
goto val_leds
boucle_led:
iled = 0
while iled < 5
if iled = 1 or 3 or 5 then high blink1:low blink2
if iled = 0 or 2 or 4 then low blink1:high blink2
iled = iled + 1
pause 1000
wend
goto val_leds
boucle1_led:
High bmf_comm1
low bmf_comm2
pause 3000
goto val_leds
boucle2_led:
low bmf_comm1
high bmf_comm2
Goto val_leds
End

The leds works but always lightning , action on button (RB0 only for the moment) don't change anything.
No blinking .
I don't know what .
thanks.