Stable ADC readings

[HankMcSpank]

Yes I have (& very good it is too) , but I'd rather have this jittery AtoD values 'cleaned up' at the source (rather than putting averaging in place to address unstability caused by avoidable factors)

[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