SOLVED: How can I reduce ADC jitter

**Demon** · - 24th February 2025, 08:20

Code:

ADCshift = NewADC0 >> 2

I shifted the results 2 bits, expecting to lose any jitter from 0 - 3, but I still get jitter.

I bet it's when a number jumps an upper bit, like 00100011 to 01000100.

I'm using 10-bit ADC, so chopping 2 bits already bring me down to 256 increments.

Bringing it down more won't solve when it's a higher jump, like 00111111 to 01000000

EDIT: Divide by 4 doesn't help either, I still get jitter, even on the voltage-divider.

**richard** · - 24th February 2025, 08:37

changing my test to rs 2 digits

jitter negligible

Code:

mean 159
readings 
0000,0000,0000,0000,0000,0000,0000,0000,0000,0000  3596  0004,0000,0000,0000,0000,0000,0000,0000,0000,0000
outliers 0000
mean 159
readings 
0000,0000,0000,0000,0000,0000,0000,0000,0000,0000  3600  0000,0000,0000,0000,0000,0000,0000,0000,0000,0000
outliers 0000
mean 159
readings 
0000,0000,0000,0000,0000,0000,0000,0000,0000,0000  3598  0002,0000,0000,0000,0000,0000,0000,0000,0000,0000
outliers 0000
mean 159

Code:

#CONFIG    __config _CONFIG1, _FEXTOSC_OFF & _RSTOSC_HFINT32 & _CLKOUTEN_OFF & _CSWEN_ON & _FCMEN_ON
    __config _CONFIG2, _MCLRE_ON & _PWRTE_OFF & _LPBOREN_OFF & _BOREN_ON & _BORV_LO & _ZCD_OFF & _PPS1WAY_OFF & _STVREN_ON & _DEBUG_OFF
    __config _CONFIG3, _WDTCPS_WDTCPS_11 & _WDTE_ON & _WDTCWS_WDTCWS_7 & _WDTCCS_LFINTOSC
    __config _CONFIG4, _WRT_OFF & _SCANE_available & _LVP_ON
    __config _CONFIG5, _CP_OFF & _CPD_OFF
#ENDCONFIG


    DEFINE OSC 32
    
    DEFINE DEBUG_REG PORTD
    DEFINE DEBUG_BIT 2      ;  if not used for pwr  
    DEFINE DEBUG_BAUD 9600
    DEFINE DEBUG_MODE 0 
    
    DEFINE ADC_BITS 10                 ' 10-bit Analog to digital
    DEFINE ADC_SAMPLEUS 50 ' Set sampling time in uS
    
    ANSELA = % 00000001                      ' Pin A0 = ADC
    TRISA = % 11101111                       ' Pin A4 = LED
    TRISD = % 11111011                       ' DEBUG 
    LATD.2 = 1                              ' DEBUG 
    clear
    LED VAR LATA.4
    i var byte
    j var word
    bucket              var WORD
    ADCinput            var WORD
    mean                var WORD
    buckets             var word[21] 
    outlier             var WORD                       
    LED = 1                                  'Proof of Life 
    PAUSE 2000  
    DEBUG 13,10,"READY",13,10 
    FVRCON = % 10000011
    ADCON0 = % 10010100
    ADREF  = % 00000000
    ADPRE  = 48
    ADCLK  = 32
    ADCAP  = 31
    LED=0


Mainloop:
    mean = 0
    for i = 0 to 9
    ADCIN 0, ADCinput
    mean = mean + ADCinput
    next
    mean = mean/40 ;average divide 4
    DEBUG "mean ",DEC mean,13,10
    for j = 0 to 3599
    ADCIN 0, ADCinput
    ADCinput=ADCinput>>2
    bucket = mean-ADCinput
    i = bucket + 10
    
    if i>20 then  
      outlier =  outlier + 1
    else
      buckets[i]=buckets[i] + 1
    endif
    'DEBUG 13,10,"mean ",DEC mean," i ",dec i," read ",dec ADCinput,13,10
    
    PAUSE 5
    next
    DEBUG "readings " ,13,10
    DEBUG  dec4 buckets[0],",", dec4 buckets[1],","  , dec4 buckets[2],",", dec4 buckets[3],"," , dec4 buckets[4],","
    DEBUG  dec4 buckets[5],",", dec4 buckets[6],","  , dec4 buckets[7],",", dec4 buckets[8],"," , dec4 buckets[9],"  "
    DEBUG  dec4 buckets[10],"  "
    DEBUG  dec4 buckets[11],",", dec4 buckets[12],","  , dec4 buckets[13],",", dec4 buckets[14],"," , dec4 buckets[15],","
    DEBUG  dec4 buckets[16],",", dec4 buckets[17],","  , dec4 buckets[18],",", dec4 buckets[19],"," , dec4 buckets[20],13,10
    DEBUG  "outliers ",dec4 outlier 
    DEBUG  13,10
    for i = 0 to 20
      buckets[i] = 0
    next
    outlier = 0
      
    GOTO Mainloop
end

**richard** · - 24th February 2025, 08:56

using the fvr gets slightly better result [mine is a 3.3v system]

Code:

mean 255
readings 
0000,0000,0000,0000,0000,0000,0000,0000,0000,0000  3600  0000,0000,0000,0000,0000,0000,0000,0000,0000,0000
outliers 0000
mean 255
readings 
0000,0000,0000,0000,0000,0000,0000,0000,0000,0000  3600  0000,0000,0000,0000,0000,0000,0000,0000,0000,0000
outliers 0000
mean 255
readings 
0000,0000,0000,0000,0000,0000,0000,0000,0000,0000  3600  0000,0000,0000,0000,0000,0000,0000,0000,0000,0000
outliers 0000
mean 255
readings 
0000,0000,0000,0000,0000,0000,0000,0000,0000,0000  3600  0000,0000,0000,0000,0000,0000,0000,0000,0000,0000
outliers 0000
mean 255
readings 
0000,0000,0000,0000,0000,0000,0000,0000,0000,0000  3600  0000,0000,0000,0000,0000,0000,0000,0000,0000,0000
outliers 0000
mean 255

Code:

#CONFIG    __config _CONFIG1, _FEXTOSC_OFF & _RSTOSC_HFINT32 & _CLKOUTEN_OFF & _CSWEN_ON & _FCMEN_ON
    __config _CONFIG2, _MCLRE_ON & _PWRTE_OFF & _LPBOREN_OFF & _BOREN_ON & _BORV_LO & _ZCD_OFF & _PPS1WAY_OFF & _STVREN_ON & _DEBUG_OFF
    __config _CONFIG3, _WDTCPS_WDTCPS_11 & _WDTE_ON & _WDTCWS_WDTCWS_7 & _WDTCCS_LFINTOSC
    __config _CONFIG4, _WRT_OFF & _SCANE_available & _LVP_ON
    __config _CONFIG5, _CP_OFF & _CPD_OFF
#ENDCONFIG


    DEFINE OSC 32
    
    DEFINE DEBUG_REG PORTD
    DEFINE DEBUG_BIT 2      ;  if not used for pwr  
    DEFINE DEBUG_BAUD 9600
    DEFINE DEBUG_MODE 0 
    
    DEFINE ADC_BITS 10                 ' 10-bit Analog to digital
    DEFINE ADC_SAMPLEUS 50 ' Set sampling time in uS
    
    ANSELA = % 00000001                      ' Pin A0 = ADC
    TRISA = % 11101111                       ' Pin A4 = LED
    TRISD = % 11111011                       ' DEBUG 
    LATD.2 = 1                              ' DEBUG 
    clear
    LED VAR LATA.4
    i var byte
    j var word
    bucket              var WORD
    ADCinput            var WORD
    mean                var WORD
    buckets             var word[21] 
    outlier             var WORD                       
    LED = 1                                  'Proof of Life 
    PAUSE 2000  
    DEBUG 13,10,"READY",13,10 
    FVRCON = % 10000010;2.048v
    ADCON0 = % 10000100
    ADREF  = % 00000011,fvr
    ADCLK  = 16; faster clk
    LED=0


Mainloop:
    mean = 0
    for i = 0 to 9
    ADCIN 0, ADCinput
    mean = mean + ADCinput
    next
    mean = mean/40 
    DEBUG "mean ",DEC mean,13,10
    for j = 0 to 3599
    ADCIN 0, ADCinput
    ADCinput=ADCinput>>2
    bucket = mean-ADCinput
    i = bucket + 10
    
    if i>20 then  
      outlier =  outlier + 1
    else
      buckets[i]=buckets[i] + 1
    endif
    'DEBUG 13,10,"mean ",DEC mean," i ",dec i," read ",dec ADCinput,13,10
    
    PAUSE 5
    next
    DEBUG "readings " ,13,10
    DEBUG  dec4 buckets[0],",", dec4 buckets[1],","  , dec4 buckets[2],",", dec4 buckets[3],"," , dec4 buckets[4],","
    DEBUG  dec4 buckets[5],",", dec4 buckets[6],","  , dec4 buckets[7],",", dec4 buckets[8],"," , dec4 buckets[9],"  "
    DEBUG  dec4 buckets[10],"  "
    DEBUG  dec4 buckets[11],",", dec4 buckets[12],","  , dec4 buckets[13],",", dec4 buckets[14],"," , dec4 buckets[15],","
    DEBUG  dec4 buckets[16],",", dec4 buckets[17],","  , dec4 buckets[18],",", dec4 buckets[19],"," , dec4 buckets[20],13,10
    DEBUG  "outliers ",dec4 outlier 
    DEBUG  13,10
    for i = 0 to 20
      buckets[i] = 0
    next
    outlier = 0
      
    GOTO Mainloop
end

**Demon** · - 24th February 2025, 09:54

Originally Posted by richard

using the fvr gets slightly better result [mine is a 3.3v system]

Code:

mean 255
readings 
0000,0000,0000,0000,0000,0000,0000,0000,0000,0000  3600  0000,0000,0000,0000,0000,0000,0000,0000,0000,0000
outliers 0000
mean 255
readings 
0000,0000,0000,0000,0000,0000,0000,0000,0000,0000  3600  0000,0000,0000,0000,0000,0000,0000,0000,0000,0000
outliers 0000
mean 255
readings 
0000,0000,0000,0000,0000,0000,0000,0000,0000,0000  3600  0000,0000,0000,0000,0000,0000,0000,0000,0000,0000
outliers 0000
mean 255
readings 
0000,0000,0000,0000,0000,0000,0000,0000,0000,0000  3600  0000,0000,0000,0000,0000,0000,0000,0000,0000,0000
outliers 0000
mean 255
readings 
0000,0000,0000,0000,0000,0000,0000,0000,0000,0000  3600  0000,0000,0000,0000,0000,0000,0000,0000,0000,0000
outliers 0000
mean 255

My readings never jitter at 0000 or 1023, always rock solid.

It's when I start taking readings within the range that things go nuts.

**richard** · - 24th February 2025, 11:13

We can't switch ADPCH manually between each Average?

not really
it needs to take the number of readings to average in an uninterrupted exclusive sequence
once the average is obtained you can set a new channel and set the device to perform a new average
or cease averaging. a sequence cannot be interrupted for an additional extra adc read

I'm trying to switch ADPCH to 111100 = AVSS (Analog Ground) before each ADCIN to see if that fixes the problem.

or makes it worse if acquisition time is inadequate or marginal , the dummy read is most successful
not sure about this chip but when does channel change occur, a delay is probably required

i don't see any form of averaging here

Code:

ADPCH = AVSS : adcin 0, ADCinput
NewADC0 = 1023 - ADCinput ' inverted so pot goes from 0 to 1024


if NewADC0 <> oldadc0 then
oldadc0 = NewADC0
ADCshift = NewADC0 / 4
LCDOUT $FE, $94+6, DEC4 oldadc0, " ", dec4 ADCshift : Pauseus 1
endif

**richard** · - 24th February 2025, 11:26

there are heaps of other ways too

mean var word
ADCinput var word

average

Code:

    mean = 0
    for i = 0 to 9
    ADCIN 0, ADCinput
    mean = mean + ADCinput
    next
    mean = mean/10 
    DEBUG "mean ",DEC mean,",",DEC mean>>2,13,10

running average

Code:

   ADCIN 0, ADCinput
   mean = mean */ 200 + ADCinput */ 55
   DEBUG "mean ",DEC mean,",",DEC mean>>2,13,10

**Demon** · - 24th February 2025, 22:54

Originally Posted by richard

...i don't see any form of averaging here...

There isn't. I thought it all happened in the background when you did ADCIN, the average was calculated, and results stored in output fields, like a normal ADCIN.

I guess you're telling me this is an on-going process, and ADCIN just gives you the average "at that point in time", but it keeps on going.

I thought setting this OFF meant we could disable continuous sampling:

16F18855

23.5.8 CONTINUOUS SAMPLING MODE

Setting the ADCONT bit in the ADCON0 register automatically retriggers a new conversion cycle after updating the ADACC register.

**richard** · - 24th February 2025, 23:50

I guess you're telling me this is an on-going process, and ADCIN just gives you the average "at that point in time", but it keeps on going.

the computational adc is more complex than that, microchip have a number of YT clips on it usages

eg

i have never had any reason to use it to date

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