Scaling ADC Result to a Set Range

**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?

**richard** · - 31st October 2015, 23:25

either setting will work the 0% error eusart option is probably best ,
if you set the baudrate regs manually ie
DEFINE HSER_SPBRG 130 ' 2400 Baud @ 16MHz, 0.0%/SPBRGH = 6
or
DEFINE HSER_SPBRG 103 ' 2400 Baud @ 16MHz, 0.17%

then DEFINE HSER_BAUD should not be used ,it may cause your setting to be overwritten

ps
baudrate error is not your display problem, you need to find out
1. how to initialise your display and how long it takes to happen
2. how to send control codes to the display ( seems $fe is not correct)

do you have any docs for the display / or a model no ?

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