Scaling ADC Result to a Set Range

[richard]

I 'm using a pickit2 to power this test so an 0,1 are unavailable (used by pickit) so I changed code to use an3
and debug via serout . needless to say it works just fine.

you may need an oscilloscope to look at your an input and power supply for noise (dvm's won't do it)
have you installed bypass caps on the regulator input/output and the pic vdd pin ?
a bit of c across the pot wiper to gnd won't hurt either

' ****************************************************************
' 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_ON & _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
ANSELA    = %00001000        ; Analog on PORTA.4(AN3) only
ADCON1    = %10100000        ; Right-justified results in 10-bits; Fosc/32 as timer;
                             ; VREF is connected to VDD
TRISA     = %111110      ' Make all pins output except for RA1 (trim pot input)
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

 lata.0=1
 pause 2000
 serout2 PORTA.0,84, ["ready",13,10 ] 
                                                          
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:
    ADCON0    = %00001101 ' Select Channel 3, Turn-On A/D
    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
    
     serout2 PORTA.0,84, ["adc ",#ADCInVal,13,10 ]
    
return