Scaling ADC Result to a Set Range

[RossWaddell]

Switched to using a 16F1825 that was previously rock solid and it's still jumping around like crazy. Could it be this 5V switching voltage regulator? This code was what I used previously to test 10-bit ADC and is what I just loaded onto the 16F1825:

' ****************************************************************
' PIC16F1825
' ****************************************************************

#DEFINE USE_LCD_FOR_DEBUG   ; comment out for non-debug use

' Vdd      -> pin 1         -> +5V   
' RC5/Rx   -> pin 5         -> EUSART receive
' RC4/Tx   -> pin 6         -> EUSART transmit (LCD)
' RA1      -> pin 12        -> trim pot input (1 uF electrolytic cap?)
' Vss      -> pin 14        -> GND
   
DEFINE OSC 16               ; Set oscillator 16Mhz

' ***************************************************************
' EUSART Settings for Tx/Rc (e.g. LCD)
' ***************************************************************

' > use Mister E PIC Multi-Calc application to get register/DEFINE settings
' > as the values are dependent on the OSC and desired baud rate

DEFINE HSER_RCSTA 90h      ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 24h      ' Enable transmit, BRGH = 1
DEFINE HSER_CLROERR 1      ' Clear overflow automatically
DEFINE HSER_SPBRG 160      ' 9600 Baud @ 16MHz, -0.08%
                               
' ***************************************************************
' Device Fuses
' ***************************************************************

#CONFIG
   __config _CONFIG1, _FOSC_INTOSC & _WDTE_ON & _PWRTE_ON & _MCLRE_OFF & _CP_OFF & _CPD_OFF
   __config _CONFIG2, _PLLEN_OFF & _STVREN_ON & _BORV_LO & _LVP_OFF
#ENDCONFIG

' ***************************************************************
' Initialization
' ***************************************************************

OSCCON    = %01111000       ; 16MHz internal osc
pause 100

APFCON0.2 = 0               ; Tx on RC4 for LCD display
APFCON0.7 = 0               ; Rx on RC5

' Some LCD serial modules need inverted data, some do not
' Enable the line below if needed, but for SparkFun SerLCD it should be
' commented out

'BAUDCON.4 = 1               ; Transmit inverted data to the Tx pin  

' From Mister E's Multi-Calc (EUSART):
' *****************************************************************
SPBRGH    = 1
BAUDCON.3 = 1               ' Enable 16 bit baudrate generator
' *****************************************************************

ANSELC    = 0               ; Digital only for all PortC pins
TRISC     = 0               ; Make all PORTC pins output

TRISA     = %00000010	    ; Make all pins output except for RA1 (trim pot input)
ANSELA    = %00000010       ; Analog on PORTA.1 (AN1) only

FVRCON    = 0               ; Fixed Voltage Reference is disabled
ADCON0    = %00000101       ; ADC enabled on AN1 (RA1) only; ADC conversion enabled
PAUSEUS 20                  ; wait for the analog switch 'glitch' to die down
ADCON1    = %10010000       ; Right-justified results in 10-bits; Fosc/8 as timer

#IFDEF USE_LCD_FOR_DEBUG
'   Display control codes for SerLCD serial LCD (SparkFun part #LCD-09395)
'   (see 'Dropbox\PBP Projects\PIC Datasheets\SerLCD_V2_5 Datasheet.pdf' 
'   for list of control codes)
    LCD_INST   CON 254       ' instruction
    LCD_CLR    CON 1         ' Clear screen
    LCD_L1     CON 128       ' LCD line 1
    LCD_L2     CON 192       ' LCD line 2
    LCD_BR_CMD CON 124       ' command character for adjusting backlight brightness
    LCD_BR_LVL CON 140       ' 140==40%
#ENDIF

' Should only need to do this one time to adjust backlight brightness
'#IFDEF USE_LCD_FOR_DEBUG
'    HSEROUT [LCD_BR_CMD, LCD_BR_LVL]
'    PAUSE 5
'#ENDIF

#IFDEF USE_LCD_FOR_DEBUG
    pause 1000
    HSEROUT [LCD_INST, LCD_CLR, "LCD Init"]
    pause 5
    HSEROUT [LCD_INST, LCD_L2, "SerLCD_V2_5"]
    pause 500
#ENDIF

ADCInVal       VAR WORD      ; stores ADCIN result read from trim pot
compVal        VAR WORD      ; stores last-changed ADC value

GOSUB Do_ADC
compVal = ADCInVal           ; set initial compare value
 
#IFDEF USE_LCD_FOR_DEBUG
    HSEROUT [LCD_INST, LCD_CLR]
    pause 5
    HSEROUT ["ADCInVal=",DEC ADCInVal,"  "]
    pause 500
#ENDIF
                                                           
Main:
    gosub Do_ADC
    pause 100

    If (compVal > (ADCInVal + 1)) or (compVal < (ADCInVal - 1)) THEn
        ' If this method of reading ADC is as rock-solid as it appears.
        ' then I can remove the +/- 1 before doing anything; it would be
        ' IF ADCInVal <> compVal
        
        ' DO SOMETHING HERE        
        compVal = ADCInVal
        
        #IFDEF USE_LCD_FOR_DEBUG
            HSEROUT [LCD_INST, LCD_CLR]
            pause 5
            HSEROUT ["new ADCInVal", LCD_INST, LCD_L2, DEC ADCInVal, "  "]
        #ENDIF
    endif
 
GOTO Main

Do_ADC:
    PAUSEUS 50              ' Wait for A/D channel acquisition time
    ADCON0.1 = 1            ' Start conversion
    
    WHILE ADCON0.1 = 1      ' Wait for it to complete
    WEND

    ADCInVal.HighBYTE = ADRESH
    ADCInVal.LOWBYTE = ADRESL
return

EDIT: Tried the standard 7805 voltage reg approach and it's more stable but still jumps around by 3-4. Could it be the settings for my serial LCD on EUSART Tx?