Battery monitoring - ever tried AN1072?

[Ioannis]

Roger, for this to work you need to get rid of the LDO and feed a 4,5Volt battery pack to the PIC. That way you will measure the Vdd voltage in respect with the VP6 input to the ADC. There is no other way to do it.

Your configuration would be:

ADCON0=%10110101   ' Here we drive the 0,6 volts to the ADC
ADCON1=%00110000   ' I prefer to be sure to have FRC for the beginning at least
VRCON= %00010000   ' Enable the VP6 reference

Now if you want to measure the Vdd, just do this:

ADCON0.1=1
while ADCON0.1: wend
Bat_Value.Byte1=ADRESH:Bat_Value.Byte0=ADRESL

But remember, you have to drop the LDO and supply your circuit from the battery directly.

Ioannis

[flotulopex]

...you need to get rid of the LDO and feed a 4,5Volt battery pack to the PIC. That way you will measure the Vdd voltage in respect with the VP6 input to the ADC.

Thanks Ioannis; I now understand what you mean.

This morning, I tried to manually setup the ADC but it was always "failing" (= giving same value all time); you just explained why it didn't work

I found an example on which I based my test code here.

I'll give your example a try

[flotulopex]

...and here are the two code example files I was talking about in my post#43 ;-)

AN1072src.zip

[towlerg]

There is a post by Darrel re this but I can't find it. I don't have any PICBasic code to hand but this in Proton might help -

  ADCON1 = %00100000                  ' ADCS=010 Fosc/32 4usec
  Symbol Go_Done = ADCON0.1
  Symbol ADON = ADCON0.0
  Symbol VP6EN = VRCON.4              ' 0.6V Reference Enable Bit

  Dim Ad_Result As ADRESL.Word        ' Convert the ADRESL register into a WORD variable
  Dim VDD       As Word


  VP6EN = 1                           ' Turn 0.6V reference ON
  ADCON0 = %10110101                  ' right justify, Vdd, select 0.6v ref, ADC on   
  DelayUS 100                         ' Wait for sample/hold capacitors to charge and VP6 to settle
  Go_Done = 1                         ' Start conversion
  While Go_Done = 1 : Wend            ' Poll the GO_DONE flag for completion of conversion
  ADCON0 = %10110100                  ' right justify, Vdd, Select 0.6v ref, ADC off   
  VP6EN = 0                           ' Turn 0.6V reference OFF
  VDD = 6144/Ad_Result                ' convert input reading to VDD voltage *VDD must be a Word
                                      ' 0.6 * 1024 = 614.4 - 6144 To get 1/10th

George

[flotulopex]

Finally YOU made it!!!

I just changed my circuit to power it directly from my variable power-supply and simulate the batterie's weakening.

@5VDC, my display shows a value of 135 and @4,2VDC (can't go lower or my display won't work anymore) I read 147.

So, except the particular init sequence for the LCD I use, the code example here under is working fine and should be quite standard.

' 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=%10110101   ' Here we drive the 0,6 volts to the ADC
    'ADCON1=%00110000   ' I prefer to be sure to have FRC for the beginning at least
    VRCON= %00010000   ' Enable the VP6 reference
    ADCON0.1=1
    WHILE ADCON0.1 : WEND
    Bat_Value.HIGHBYTE = ADRESH : Bat_Value.LOWBYTE = ADRESL
    LCDOUT $FE,2,DEC4 Bat_Value
    PAUSE 1000
GOTO MAIN

END

Using the internal 0,6V reference:
- 0,8Vbatt difference = 12 value change
+ no external components

Using an external voltage divider:
+ 0,8Vbatt difference = 84 value change
- external components


Thanks a lot for all your help

[flotulopex]

...and while testing things, here is something I just tried based on the code in my previous post using the ADCIN command:

' Start program

MAIN:
    ADCON1 = %00110000   ' I prefer to be sure to have FRC for the beginning at least
    VRCON  = %00010000   ' Enable the VP6 reference
    ADCIN 13, Bat_Value  ' ADCON0 = %10110100 where bits 5:2 are the 0,6V reference's channel address (1101 = 13)
    LCDOUT $FE,2,DEC5 Bat_Value
    PAUSE 1000
GOTO MAIN

END

The results are @5VDC I read 8640 and 9790 @4,2VDC (?!) but it looks to work somehow.

[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