Battery voltage monitoring for use on 16F1825

[longpole001]

Any feed back on why the ACD is not working , how to workout the calculation for the what result i should see ?

[prstein]

I notice a couple of oddities in your code that may (or may not!) be part of the problem. You are using the PBP ADCIN command but not any of the PBP defines. I don't know if PBP needs the defines beyond setting some register bits which you do directly. Below is a gentle re-arrangement of your code, trying to follow the exact order recommended in the manual. Also, it explicitly waits until the FVR is ready and, instead of using ADCIN, manually starts the conversion, waits for it to finish, and then reads the result.

' ---------- Gets a Voltage reading on Port1.0 --------- 
 
 ' Note:  - Application circuit has a 3.3v voltage reg fitted so could use VDD as Vref in ASCON1 register
 '        - have used the ADC Fixed Voltage Ref Modual in 16F1825.
 '        - PortA.0 ia also used as Digital Output of Power LED active low via Pch - Mosfet
 '        - Supply Voltage input range is 8.1V - 3.5V to Voltage divider ( Vsupply --> 27k -|- 15K -- GND)  giving ADC input on PORTA.0 = 2.8 - 1.4V
 '                                                                       (                PortA.0        )
 
 Get_volts :
  TRISA.0 = 1           ' setup Port A.0 input=1,output=0 for I/O pins ( Note RA3 - is input only (digital)- refer spec)
  ANSELA =  %00000001           ' Set Port A.0 - Analoge I/O  , 0 = Digital  1 = Analog
  
  FVRCON  = %10000010           ' Bit 7 =1 enable Fixed Voltage Ref Modual, Bit 6 = VRef ready bit =1 always ok on 16F1825, Bit 5 - Temp indicator 1= enable/0 = disable
                                ' Bit 4 = Temp Indicator Range Sel 0=Vout -Low range / 1= Vout -High range , Bit 3-2 = 00( DAC Fixed volt sel )
                                ' Bit 1-0 = 10 - ADC Fixed Vref of 2.048v
  
while FVRCON.6 = 0 : wend  'wait for FVR to be ready
                                    
  ADCON0 =  %00000001           ' bit 7 -N/A , Bit 6-2 = ADC chan Sel /Tempature output /FVR output = AN0 sel = 00000 ,
                                ' Bit 1 - Go/_done status flag - 1 = Go do ADC / 0 = Done ADC , Bit 0 = Enable ADC = 1  / 0 = Disable ADC
  
  ADCON1 =  %10100011           ' bit 7 = 1 ADFM ( ADRESH, ADRESL - right justify ).Bit 6-4 ADCS = 010 - Fosc/32 conversion clock 
                                ' Bit3 - N/A , Bit2 = 0 (Vref- is connected to Vss) , Bit1-0 = 11 - Vref+ connected to FVR Modual 
  
  
  pauseus 10                    ' allow Vref to stablise - ??? - not required for the 16F1825/29 ?? 
  
  
'  adcin  0, ADval               ' Read PortA.0 value into variable , this applies the fixed voltage ref (via ADCON0,ADCON1,FVRCON)
'                                ' to comparitor and ADC pin selected and gives result   ???
  ADCON0.0 = 1    'start the conversion
  while ADCON0.0 = 1 : wend   'wait for it to finish
  ADVal.byte0 = ADRESL
  ADVal.byte1 = ADRESH
  
   write $01 ,ADval.byte0       ' debug of voltage measurement - lower byte 
   write $02 ,ADval.byte1       ' debug of voltage measurement - upper byte 
   
     If ADval <= 1024 then      ' Have no idea of the value its going to get ??  , but if below value of 1.6V ( 4.5v Vsupply) then set Power low values
           Pulse_off  = 500     ' Set Pulse_off duration to 500us to signal power low to IR_RX 
           Flash_rate =  10     ' Set Power Led toggle to fast rate to show low power  
        Else 
           Pulse_off  = 276     ' Set Pulse_off duration to 300us( adj) to signal NOT power low to IR_RX 
           Flash_rate = 100     ' Set Power Led toggle to Normal rate to show NOT low power   
     endif   
      
                                ' Restore PortA.0 to digital . ACD OFF etc 
   ADCON0 =  %00000000          ' Set ADC to Disable  - Bit 0 = Enable ADC = 1  / 0 = Disable ADC
   ANSELA =  %00000000          ' Set Port A.0 = 0 Digital, 0 = Digital  1 = Analog
   TRISA.0 = 0          ' setup Port A.0 input=1,output=0 for I/O pins ( Note RA3 - is input only (digital)- refer spec) 
 
 return

Hope this helps...

Best Regards,
Paul

[peterdeco1]

A while back I added a battery voltage tester to an existing circuit board. I didn't have a choice - the PIC was operating from the battery directly without a regulator at 5.4V (6V battery through series protection diode). Using a jumper wire I connected the ADC to an on-board regulator in another part of the circuit. Now it measured voltage in reverse; the lower the battery voltage, the higher the ADC reading. With trial and error I found 167 to be my alert number for low battery.

ADCIN 1, BATTERYCONDITION
IF BATTERYCONDITION >= 167 THEN HIGH PORTB.0.

Portb.0 connected to Nch FET. For low voltages I always use a logic-level FET with a very low gate threshold voltage. I prefer IRLZ44N. It's a power transistor that I use to supply 2A without needing a heatsink. Just barely gets warm at that current.