SOLVED: How can I reduce ADC jitter

[richard]

i tried the burst mode averaging method. very nice if you don't need the adc for anything else, it would be ideal for monitoring a lifepo4 battery during all phases of discharge/charging/float. no great advantage for multiple inputs that i can see

[Demon]

i tried the burst mode averaging method. very nice if you don't need the adc for anything else, it would be ideal for monitoring a lifepo4 battery during all phases of discharge/charging/float. no great advantage for multiple inputs that i can see

I'm going to see about using something like your MEAN average example. I had something like that a while ago (inspired by Melanie), but I had noisy power supplies. The TPS56637 works nicely, so I was hoping ADC2 could make my life easier.

[richard]

I only have a few 1000uF electrolytics, so I put 2 on each rail, same ADC flutter of mostly 1, sometimes 2.

+- 2 counts is as good as it will ever get for raw adc reads on a breadboard, if you right shift 2 bits that's a 256 count resolution that should be very stable

the scope is your friend here , measure the AC noise. every 5mV of noise on the rail and/or the pot wiper is +- 1 more count

[richard]

note some of the variations you are calling flutter are actually "Quantization noise" and can never be eliminated from the adc process,
the best adc result is always +-1 count. at the expense of some resolution[level bandwidth etc] you can filter it out "mostly" people with "hifi" ears reckon they can hear it on the best of cd recoding's , yet scratched vinyl records are pure, go figure. as a true cloth eared pariah i call wtf

[Ioannis]

On a PCB of a irrelevant project I tested the simple ADCin and display the result on the LCD.

As Richard says the +/-1 LSB is what I get with no process. Occasionaly 2 LSBs.

I just sample every sec. and display it.

Of course the PCB is double sided with lot of ground, a cap on the ADC input pin and linear 5Volt regulator. So any external noise is minimized.

Breadboards are just a noise antennas and never give clean results.

Ioannis

[Demon]

Ultimately, the system has to be able to read ADC while managing to 2-3 LED strips and 4 LCDs with PWM.

I'm trying a double PSU approach to see if the input PIC (right) can keep line noise to a minimum, and have all output functions on the output PIC (left).

Input functions will consume very little current, it's the output functions that will consume a lot more, and have multiple PWMs.




The only unknown is the rotary encoders; no idea if their rapid ON-OFF will create noise. I can always move them over to the output PIC.

At worse, I'd end up with a "clean" PIC, and a "noisy" PIC instead of input/output.

[Demon]

I've gone back to getting a "basic" ADC routine working for 1 voltage-divider and 2 pots (for a better sampling).

#CONFIG
    __config _CONFIG1, _FEXTOSC_OFF & _RSTOSC_HFINT32 & _CLKOUTEN_OFF & _CSWEN_OFF & _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_OFF & _WDTCWS_WDTCWS_7 & _WDTCCS_LFINTOSC
    __config _CONFIG4, _WRT_OFF & _SCANE_available & _LVP_OFF
    __config _CONFIG5, _CP_OFF & _CPD_OFF
#ENDCONFIG

DEFINE OSC 32

DEFINE  ADC_BITS 10                 ' 10-bit Analog to digital
DEFINE  ADC_SAMPLEUS 50             ' Set sampling time in uS

DEFINE  HSER_RXREG PORTC
DEFINE  HSER_RXBIT 7
DEFINE  HSER_TXREG PORTC
DEFINE  HSER_TXBIT 6

DEFINE  HSER_RCSTA 90h              ' Enable serial port & continuous receive
DEFINE  HSER_TXSTA 24h              ' Enable transmit, BRGH = 1
Define  HSER_BAUD 115200
DEFINE  HSER_CLROERR 1              ' Clear overflow automatically
DEFINE  HSER_SPBRGH  0
DEFINE  HSER_SPBRG  68

;--- Setup registers -----------------------------------------------------------

BAUDCON.3 = 1                       ' Enable 16 bit baudrate generator

FVRCON = %10000011                  ' FIXED VOLTAGE REFERENCE CONTROL REGISTER
'   bit 7   FVREN: Fixed Voltage Reference Enable bit
'       --->    1 = Fixed Voltage Reference is enabled
'   bit 1-0 ADFVR<1:0>: ADC FVR Buffer Gain Selection bit
'       --->    11 = ADC FVR Buffer Gain is 4x, (4.096V)(2)

ADCON0 = %10000100                  ' ADC CONTROL REGISTER 0
'   bit 7   ADON: ADC Enable bit
'        --->   1 = ADC is enabled
'   bit 2   ADFRM0: ADC results Format/alignment Selection
'        --->   1 = ADRES and ADPREV data are right-justified

ADCON2 = %00000000                  ' ADC CONTROL REGISTER 2
'   bit 2-0 ADMD<2:0>: ADC Operating Mode Selection bits(1)
'        --->   000 = Basic (Legacy) mode

ADCLK = %00111111                   ' ADC CLOCK SELECTION REGISTER
'   bit 5-0 ADCCS<5:0>: ADC Conversion Clock Select bits
'        --->   111111 = FOSC/128

ADREF = %00000011                   ' ADC REFERENCE SELECTION REGISTER
'   bit 4 ADNREF: ADC Negative Voltage Reference Selection bit
'        --->   0 = VREF- is connected to AVSS
'   bit 1-0 ADPREF: ADC Positive Voltage Reference Selection bits
'        --->   11 = VREF+ is connected to FVR_buffer 1

ADPCH = %00000000                   ' ADC POSITIVE CHANNEL SELECTION REGISTER
'        --->   000000 = ANA0

ANSELA = %00000111                      ' Pin A2 = ADC (B5K)
                                        ' Pin A1 = ADC (B5K)
                                        ' Pin A0 = ADC (voltage divider)
ANSELB = %00000000
ANSELC = %00000000

TRISA = %00000111                       ' Pin A2 = ADC input 2
                                        ' Pin A1 = ADC input 1
                                        ' Pin A0 = ADC input 0
TRISB = %00000000                       ' Pin B7 = ...not available, ICSPDAT
                                        ' Pin B6 = ...not available, ICSPCLK
TRISC = %11000000                       ' Pin C7 = RX      *** Datasheet requirement, INPUT ***
                                        ' Pin C6 = TX      *** Datasheet requirement, INPUT ***

ADCinput            var WORD
ADCtot              var WORD
ADCcalc             var WORD
ADCdiff             var WORD
ADCLoop             VAR BYTE
OldADC0             var WORD
OldADC1             var WORD
OldADC2             var WORD

    Pause 500                           ' Let PIC and LCD stabilize
    ADCinput = 0    : ADCdiff = 0
    OldADC0 = 9999  : OldADC1 = 9999  : OldADC2 = 9999

Mainloop:

rem                 ADC0, 4K7-4K7 voltage divider

    adcin 0, ADCinput : Pauseus 1               ' preliminary ADCIN to establish channel used
    ADCtot = 0

    FOR ADCLoop = 0 TO 15                       ' Load 16 ADC values
        adcin 0, ADCinput : Pauseus 1
        ADCtot = ADCtot + ADCinput
    NEXT ADCLoop
    ADCcalc = ADCtot / 16                       ' Average out

    if ADCcalc < oldADC0 then                   ' Calculate change in ADC
        ADCdiff = oldadc0 - ADCcalc
    else
        ADCdiff =  ADCcalc - oldadc0
    endif

    IF  (ADCdiff > 2) or _                      ' Check for Diff over 2 ... OR
       ((adccalc <> oldadc0) and _              '   ADC value changed ...   AND
         (adccalc = 0 or adccalc = 1023)) then  '   Reached end of rotation
        hserout [   "OldADC0:",     DEC4 oldadc0, "  ", _
                    "                            ", _
                    "ADCin:",       DEC4 ADCcalc, "  ", _
                    "Diff:",        dec4 ADCdiff, "  ", _                        
                    "Sum:",         Dec5 ADCtot, 10]                             
        while TXSTA.1 = 0               ' Check TRMT bit
        wend
        oldADC0 = ADCcalc
    endif
 
rem                 ADC1, B5K pot

    adcin 0, ADCinput : Pauseus 1               ' preliminary ADCIN to establish channel used
    ADCtot = 0

    FOR ADCLoop = 0 TO 15                       ' Load 16 ADC values
        adcin 1, ADCinput : Pauseus 1
        ADCtot = ADCtot + ADCinput
    NEXT ADCLoop
    ADCcalc = ADCtot / 16                       ' Average out

    if ADCcalc < oldADC1 then                   ' Calculate change in ADC
        ADCdiff = oldadc1 - ADCcalc
    else
        ADCdiff =  ADCcalc - oldadc1
    endif

    IF  (ADCdiff > 2) or _                      ' Check for Diff over 2 ... OR
       ((adccalc <> oldadc1) and _              '   ADC value changed ...   AND
         (adccalc = 0 or adccalc = 1023)) then  '   Reached end of rotation
        hserout [   "              ", _
                    "OldADC1:",     DEC4 oldadc1, "  ", _
                    "              ", _
                    "ADCin:",       DEC4 ADCcalc, "  ", _
                    "Diff:",        dec4 ADCdiff, "  ", _                        
                    "Sum:",         Dec5 ADCtot, 10]                             
        while TXSTA.1 = 0               ' Check TRMT bit
        wend
        oldADC1 = ADCcalc
    endif

rem                 ADC2, B5K pot

    adcin 2, ADCinput : Pauseus 1               ' preliminary ADCIN to establish channel used
    ADCtot = 0

    FOR ADCLoop = 0 TO 15                       ' Load 16 ADC values
        adcin 2, ADCinput : Pauseus 1
        ADCtot = ADCtot + ADCinput
    NEXT ADCLoop
    ADCcalc = ADCtot / 16                       ' Average out

    if ADCcalc < oldADC2 then                   ' Calculate change in ADC
        ADCdiff = oldadc2 - ADCcalc
    else
        ADCdiff =  ADCcalc - oldadc2
    endif

    IF  (ADCdiff > 2) or _                      ' Check for Diff over 2 ... OR
       ((adccalc <> oldadc2) and _              '   ADC value changed ...   AND
         (adccalc = 0 or adccalc = 1023)) then  '   Reached end of rotation
        hserout [   "                            ", _
                    "OldADC2:",     DEC4 oldadc2, "  ", _
                    "ADCin:",       DEC4 ADCcalc, "  ", _
                    "Diff:",        dec4 ADCdiff, "  ", _                        
                    "Sum:",         Dec5 ADCtot, 10]                             
        while TXSTA.1 = 0               ' Check TRMT bit
        wend
        oldADC2 = ADCcalc
    endif

  GOTO Mainloop

end

Checklist:

- PIC 16F18855,
- used legacy ADC (no ADC2),
- did not touch VREFs,
- used FVR 4x with 5 VDC in,
- used FOSC / 128,
- used average of 16 ADC readings,
- removed all LCD logic (used for debugging),
- used USART to show results
- added PAUSEUS 1 after all ADC operations - THIS NEEDS TO BE VERIFIED IF IT'S NECESSARY, it was just to make sure things worked.

ADC readings on the voltage-divider and 2 rotary pots did not "drift/vary/whatever" more than 2.

I still have to:

- try with slide pots, just to see if that fixed their "irregularities" that I experienced in the past.
- reconnect the 2nd breadboard that displays to LCD with backlight PWM, and PWMs 2 LED strips.


EDIT: This was working perfectly with the voltage divider (ADC0) and pot 2 (ADC2), now that I've put back in pot 1 (ADC1), the 2 pots don't reach 0 and stop at 2.

ARGH...