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Need help with Volt reading.

Thread starter #1
Hello Friends

PIC16f690 @ 4mhz internal clock

Reading voltage at AN9 0vdc ~ vdc 4.46
Vdd as ref @ 4.46vdc
AN9 input via 5k pot with vdd as 4.46 and Vss as 0.00

Code:
'PIC16F690

Define CONFIG = 0x30f4
Define CLOCK_FREQUENCY = 4
AllDigital

Define SIMULATION_WAITMS_VALUE = 1
'------------------------------------
Dim digi3 As Byte
Dim digi2 As Byte
Dim digi1 As Byte
Dim digi0 As Byte
Dim temp As Word
Dim binval As Word
Dim volt As Word
'------------------------------------
ADCON0.ADON = 1
ADCON0.VCFG = 0
ADCON0.ADFM = 0
ADCON1 = 0x00

ADCON1 = %01010000
ANSELH.ANS9 = 1

TRISA = %00000000
TRISB = %00000000
TRISC = %10000000
'------------------------------------
Define LCD_BITS = 4
Define LCD_DREG = PORTC
Define LCD_DBIT = 0
Define LCD_RSREG = PORTA
Define LCD_RSBIT = 0
Define LCD_RWREG = 0
Define LCD_RWBIT = 0
Define LCD_EREG = PORTA
Define LCD_EBIT = 2
Define LCD_READ_BUSY_FLAG = 1
Lcdinit
Lcdcmdout LcdClear


main:  'main loop
    
    Gosub readadc
    Gosub bin2asc
    Lcdcmdout LcdClear
    Lcdout "Volt: ", digi3, digi2, ".", digi1, digi0

    Goto main

    End

readadc:

    Adcin 9, volt
    
        If volt > 0 Then
        
            volt = volt / 2
            
            binval = volt
        Endif
    Return

bin2asc:

digi3 = binval / 1000
temp = binval Mod 1000

digi2 = temp / 100
temp = temp Mod 100

digi1 = temp / 10
digi0 = temp Mod 10

digi3 = digi3 Or 0x30
digi2 = digi2 Or 0x30
digi1 = digi1 Or 0x30
digi0 = digi0 Or 0x30
    Return
The voltage on the DMM at pin AN9 and the result is off a few milli volts
any ideas ?

Thanx
Mastero
 

JonSea

Well-Known Member
Most Helpful Member
#3
I believe he's using Vdd as the reference, which happens to be 4.46V.

The resolution of a 10-bit ADC is Vref/1024, in this case:

4.46/1024 = 0.00436V × 1000mV/V = 4.36mV.

So your measurements can't be better than a few mV off. If you need better results, you need an ADC with more bits.
 

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