Battery monitoring - ever tried AN1072?

[towlerg]

The ADC is 10 bit, the largest value you can read is 1023 (10 1's). BTW check to table in the ADC section re. recommended ADC clock source, at 8 Mhz use Fosc/16 or Fosc/32. See note re using FRC as a clock source above 1Mhz.

You seem to have missed out the conversion to 0v1.

George

[Ioannis]

Are you sure that you still have right justification? Maybe you have accidentaly set the ADCON.7 to zero?

In general the bigger number for lower voltage is correct. Since you have the same 0,6 volts at the ADC input, lowering the Vref (through Vdd) will give bigger ADC result.

But not more than 1023 as George stated.

Ioannis

[flotulopex]

Thanks Ioannis and George,

Here is the corected and 100% working code example using ADCIN:

' PIC 16F690 Fuses
@ __config _FCMEN_OFF &_IESO_OFF &_CPD_OFF &_WDT_OFF &_HS_OSC &_BOR_OFF &_CP_OFF &_PWRTE_OFF &_MCLRE_OFF

'-------------------------------------------------------------------------------
' Registers   76543210
OPTION_REG = %10000000 'OPTION register
ANSEL      = %00000000 'Select analog inputs Channels 0 to 7
ANSELH     = %00000000 'Select analog inputs Channels 8 to 11
WPUA       = %00000000 'Select weak pull-ups
WPUB       = %00000000 'Select weak pull-ups
ADCON0     = %00000000 'AD Module
ADCON1     = %00000000 'AD control register
CM1CON0    = %00000000 'Comparator1 Module
CM2CON0    = %00000000 'Comparator2 Module
INTCON     = %00000000 'INTerrupts CONtrol
TRISA      = %00000000 'Select Input/Output (0 to 5)
PORTA      = %00000000 'Set High/Low (0 to 5)
TRISB      = %00000000 'Select Input/Output (4 to 7)
PORTB      = %00000000 'Set High/Low (4 to 7)
TRISC      = %00000000 'Select Input/Output (0 to 7)
PORTC      = %00000000 'Set High/Low (0 to 7)

'-------------------------------------------------------------------------------
' Defines
DEFINE OSC 8

DEFINE LCD_DREG PORTC  'LCD data port 
DEFINE LCD_DBIT 4      'LCD data starting PORT.bit (0 or 4)
DEFINE LCD_RSREG PORTC 'LCD register select port 
DEFINE LCD_RSBIT 3     'LCD register select bit 
DEFINE LCD_EREG PORTC  'LCD enable port 
DEFINE LCD_EBIT 2      'LCD enable bit 
DEFINE LCD_BITS 4      'LCD bus size 4 or 8

DEFINE ADC_BITS 10     'Number of bits in ADCIN result

'-------------------------------------------------------------------------------
' Init display

' ELECTRONIC ASSEMBLY DOGM081 LCD display Mandatory settings
'  See datasheet for circuitry changes by 5V or 3,3V operation
PAUSE 1000      'Time to settle Vdd (THIS IS CRUCIAL FOR THIS DISPLAY!!!)
LCDOUT $FE, $29 'Function Set: 4 bits bus mode
LCDOUT $FE, $1C 'Bias set
LCDOUT $FE, $52 'Power control + Contrast (HiByte)(for 5V=$52 or 3,3V=55)
LCDOUT $FE, $69 'Follower control (5V=$69/3,3V=6D)
LCDOUT $FE, $78 'Contrast (LowByte)

'-------------------------------------------------------------------------------
' Variables
Bat_Value   var word 'holds ADC value
Bat_Value   = 0

'-------------------------------------------------------------------------------
' Start program

MAIN:
    ADCON0 = %10000000   ' Here we drive the 0,6 volts to the ADC
    VRCON  = %00010000   ' Enable the VP6 reference
    ADCIN 13, Bat_Value  ' Select the VP6 channel's address ADCON0 = %xx1101xx
    Bat_Value.HIGHBYTE = ADRESH : Bat_Value.LOWBYTE = ADRESL
    LCDOUT $FE,2,DEC4 Bat_Value
    PAUSE 1000
GOTO MAIN

END

[towlerg]

Did you see how to convert he ADC count in Bat_Value to volts?

I see you are still not using a recommended value for ADCS in ADCON1.

George

[flotulopex]

Yes George,

For any reason, either ADCON1.ADCS setting will affect the results.

For those interested in the maths (where "2n" is 1024 because I use 10bits in ADC):


Regarding my results and comparing them to the table A-1 (Appendix A: AC Result Table in AN1072), something must be wrong.

A 135 ADC result corresponds to 4,52V and 147 to 4,16V (?!).

Grrrrrr! I didn't notice I hadn't removed the voltage regulator on my breadboard. My PICkit2 programmer delivers 4,78VDC (even if it shows 5V in the "VDD PICkit2" field) so the "new" ADC values I get now seem to be much closer to what they are supposed to be "on the paper".

For 4,82V displayed on my FLUKE87, the ADC result is now 127 (exact as table A-1) and @4,31V I get 142 (exact as table A-1).

((1024 - 1) / 4,82) * 0,6 = 127 and ((1024 - 1) / 4,31) * 0,6 = 142

[Ioannis]

Glad you did it Roger! Bravo!

Ioannis

[towlerg]

For any reason, either ADCON1.ADCS setting will affect the results.

I don't know the internals of ADCIN, but unless it sets the ADCS bits to something else, you're ADC clock source will be Fosc/2 which at 8Mhz will give a Tad of 250ns. Fosc/16 or Fosc/32 are recommended.

George