Scaling ADC Result to a Set Range

**RossWaddell** · - 29th October 2015, 22:00

Thanks Henrik! I'll try that tonight.

**RossWaddell** · - 30th October 2015, 00:18

since I might have to change that constant of 39332, how did you arrive at that value?

**RossWaddell** · - 30th October 2015, 01:48

Your formula works, Henrik - not that should come as a surprise. Knowing how you arrived at that constant in the expression would help me me adjust for different resolutions.

Here's the code I used to test Henrik's formula:

Code:

#DEFINE USE_LCD_FOR_DEBUG   ; comment out for non-debug use
   
' ***************************************************************
' Pin Connections
' ***************************************************************

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

DEFINE HSER_TXSTA   20h     ; Set transmit status and control register
DEFINE HSER_BAUD    2400    ; Set baud rate
                               
' ***************************************************************
' 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

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

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

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    = %00110000       ; Left-justified results in 8-bits; Frc as timer
 
#IFDEF USE_LCD_FOR_DEBUG
    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
#ENDIF

MotorDuty   VAR BYTE        ; Actual duty cycle for motor
ADCInVal    VAR BYTE        ; stores ADCIN result read from trim pot
MinDuty     CON 100         ; Minimum speed to rotate motor for this application
                                                              
Main:
    gosub Do_ADC
    pause 100
    GOSUB Map_ADC_Val_to_PWM_Duty
 
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 = ADRESH

    return


Map_ADC_Val_to_PWM_Duty:
'   Arduino Map function to emulate:
'   ===============================
'   map(value, fromLow, fromHigh, toLow, toHigh)

'   long map(long x, long in_min, long in_max, long out_min, long out_max)
'   {
'     return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
'   }

'    MotorDuty = (ADCInVal - 0) * (MaxDuty - MinDuty)/(MaxADCVal - 0) + MinDuty
    MotorDuty = (ADCInVal ** 39322) + MinDuty  ' Same as 100 + ADCInValue * 0.600006 but likely faster than 100+ADCInValue*6/10
    
    #IFDEF USE_LCD_FOR_DEBUG
        HSEROUT [LCD_INST, LCD_CLR]
        pause 5
'        HSEROUT ["ADCInVal=", DEC ADCInVal, "       ", 13, 10] ; Send text followed by carriage return and linefeed
        HSEROUT ["ADCInVal=", DEC ADCInVal, "       ", 13, 10, "MotorDuty=", DEC MotorDuty]
'        pause 5
'        HSEROUT ["MotorDuty=", DEC MotorDuty, "       "] ; Send text followed by carriage return and linefeed
    #ENDIF

    RETURN

Here's the annoying part - no matter how many searches I do here I can't find the syntax to print on the 2nd line of the LCD. With the above the screen just seems to flicker (which also doesn't make sense - with the ADC method here it usually results in a rock-solid value; in other words, it doesn't change until I actually move the wiper arm. I know it's unrelated to the original post, but any ideas?

**HenrikOlsson** · - 30th October 2015, 06:16

Hi,
Think of the ** operator as multiplying by units of 1/65536. 0.6*65536=39322.

As for printing to second line of the LCD you're obviously using some sort of serial interface display(?) which I know nothing about but if I'd make a guess based on your defined constants you'd do something like

Code:

HSEROUT[LCD_INST, LCD_L2, "2d Line"]

/Henrik.

**RossWaddell** · - 30th October 2015, 23:11

Thanks Henrik. You'd think I would have noticed that constant. Changing the HSEROUT to this:

Code:

#DEFINE USE_LCD_FOR_DEBUG   ; comment out for non-debug use

' ***************************************************************
' Pin Connections
' ***************************************************************

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

DEFINE HSER_TXSTA   20h     ; Set transmit status and control register
DEFINE HSER_BAUD    2400    ; Set baud rate
                               
' ***************************************************************
' 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

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

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

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    = %00110000       ; Left-justified results in 8-bits; Frc as timer
 
#IFDEF USE_LCD_FOR_DEBUG
    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
#ENDIF

MotorDuty   VAR BYTE        ; Actual duty cycle for motor
ADCInVal    VAR BYTE        ; stores ADCIN result read from trim pot
MinDuty     CON 100         ; Minimum speed to rotate motor for this application
                                                              
Main:
    gosub Do_ADC
    pause 100
    GOSUB Map_ADC_Val_to_PWM_Duty
 
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 = ADRESH

    return


Map_ADC_Val_to_PWM_Duty:
'   Arduino Map function to emulate:
'   ===============================
'   map(value, fromLow, fromHigh, toLow, toHigh)

'   long map(long x, long in_min, long in_max, long out_min, long out_max)
'   {
'     return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
'   }

'    MotorDuty = (ADCInVal - 0) * (MaxDuty - MinDuty)/(MaxADCVal - 0) + MinDuty
    MotorDuty = (ADCInVal ** 39322) + MinDuty  ' Same as 100 + ADCInValue * 0.600006 but likely faster than 100+ADCInValue*6/10
    
    #IFDEF USE_LCD_FOR_DEBUG
        HSEROUT [LCD_INST, LCD_CLR]
        pause 5
'        HSEROUT ["ADCInVal=", DEC ADCInVal, "       ", 13, 10] ; Send text followed by carriage return and linefeed
        HSEROUT ["ADCInVal=", DEC ADCInVal, "       ", LCD_L2, "MotorDuty=", DEC MotorDuty, "       ", 13, 10]
'        pause 5
'        HSEROUT ["MotorDuty=", DEC MotorDuty, "       "] ; Send text followed by carriage return and linefeed
    #ENDIF

    RETURN

I can now see the 2nd line, but it's not starting at the first character position and there's a weird character there before 'MotorDuty'. It might be related to the spaces after the first line, but I'm not sure. Also, the first line seems to be refreshing/fluttering even when I'm not moving the trim pot. I have to admit, I use my serial LCD so infrequently that I'm a noobie where it comes to this.

Here's a video of what the screen looks like.

**richard** · - 31st October 2015, 00:13

try
HSEROUT ["ADCInVal=", DEC ADCInVal, " ", LCD_INST,LCD_L2, "MotorDuty=", DEC MotorDuty, " ",13,10]

**RossWaddell** · - 31st October 2015, 14:25

I used the HSEROUT line exactly as above and when I turn on the power:

Name: IMG_3667.JPG
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Size: 109.9 KB

Then, as I turn the trim pot wiper:

Name: IMG_3669.JPG
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Size: 113.4 KB

The serial LCD is 2400 baud by default and that's what I have set in code, but maybe there's some timing issues?

**RossWaddell** · - 31st October 2015, 20:26

If I'm using a PIC16F1825 how do I know whether to use the USART or EUSART settings from Mister E's PIC Multi-Calc application? This is what I have set currently:

Code:

DEFINE OSC 16               ; Set oscillator 16Mhz

DEFINE HSER_TXSTA   20h     ; Set transmit status and control register
DEFINE HSER_BAUD    2400    ; Set baud rate
DEFINE HSER_CLROERR 1

OSCCON    = %01111000       ; 16MHz internal osc

PAUSE 100

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

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

I see that Mister E's app doesn't use DEFINE HSER_BAUD. For USART I get:

Code:

DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 20h ' Enable transmit, BRGH = 0
DEFINE HSER_SPBRG 103 ' 2400 Baud @ 16MHz, 0.17%
DEFINE HSER_CLROERR 1 ' Clear overflow automatically

For EUSART:

Code:

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 130 ' 2400 Baud @ 16MHz, 0.0%
SPBRGH = 6
BAUDCON.3 = 1         ' Enable 16 bit baudrate generator

Which should I use? And should I continue to use DEFINE HSER_BAUD which I think I got from this board a ling time ago?

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