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Voltage Information with FVR in PIC18F46K40

 
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sema_tufan



Joined: 03 Mar 2020
Posts: 14
Location: turkey

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Voltage Information with FVR in PIC18F46K40
PostPosted: Tue Dec 22, 2020 5:34 am     Reply with quote

How can I learn the voltage information from the instant battery with the FVR using the PIC18F46K40 processor?
I've done it before in PIC18f25k20. I pasted the codes I used into my PIC18f46k40 processor project. 0 read.

Code:
void batteryStatus()
{
FVREN=TRUE; //enable the FVR
setup_adc(ADC_CLOCK_DIV_16|VSS_VDD);
set_adc_channel(15); //select FVR as input channel
delay_us(30); //needs 15uSec minimum when reading FVR
value=read_adc(ADC_START_AND_READ);
supply=(1.2/value)*1024;
setup_adc_ports(NO_ANALOGS); //
}
temtronic



Joined: 01 Jul 2010
Posts: 8091
Location: Greensville,Ontario

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PostPosted: Tue Dec 22, 2020 5:53 am     Reply with quote

Quick comment..
I don't use that PIC, never used FVR either but....

this...
Quote:
setup_adc_ports(NO_ANALOGS); //

just looks wrong !

After the function executes, you won't have ANY ADC ???

Would have to read the ADC chapter to see if FVR can be read with 'no_analogs' selected...
sema_tufan



Joined: 03 Mar 2020
Posts: 14
Location: turkey

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PostPosted: Tue Dec 22, 2020 6:04 am     Reply with quote

setup_adc_ports (NO_ANALOGS); I copied this line extra. I did not add such a line of code in the project, but I always get 0 data.


temtronic wrote:
Quick comment..
I don't use that PIC, never used FVR either but....

this...
Quote:

setup_adc_ports(NO_ANALOGS); //

just looks wrong !

After the function executes, you won't have ANY ADC ???

Would have to read the ADC chapter to see if FVR can be read with 'no_analogs' selected...
temtronic



Joined: 01 Jul 2010
Posts: 8091
Location: Greensville,Ontario

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PostPosted: Tue Dec 22, 2020 6:17 am     Reply with quote

Is the variable 'supply' a floating point ?

One debug procedure is to breakdown the line
Code:
supply=(1.2/value)*1024;

into smaller parts and display the results.

1) display value // the actual ADC reading
2) 1.2/value // don't know where 1.2 comes from...
3) supply // which you say is zero

Be sure to format the display properly based on the variable types !

If it still doesn't work, code and post a small program that shows the problem, something we can 'cut/paste' compile/test.

Jay
PCM programmer



Joined: 06 Sep 2003
Posts: 21450

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PostPosted: Tue Dec 22, 2020 1:04 pm     Reply with quote

CCS has a defined constant for the FVR and it's not 15.
Look in 18F46K40.h, in the SET_ADC_CHANNEL section. It says:
Quote:
// Constants used in SET_ADC_CHANNEL() are:
// either use the channel number or one of the following
#define AVSS_CHANNEL 0x3C
#define TEMPERATURE_INDICATOR 0x3D
#define DAC_CHANNEL 0x3E
#define FVR_CHANNEL 0x3F

This also matches the 18F46K40 data sheet's ADC channel table.

The proper way to code it is not to use magic numbers.
Instead, do it like this:
Code:
set_adc_channel(FVR_CHANNEL);
sema_tufan



Joined: 03 Mar 2020
Posts: 14
Location: turkey

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PostPosted: Tue Dec 22, 2020 1:21 pm     Reply with quote

Thank you for your answers. I solved the problem with this code on PIC18f46k40 processor.
Code:

  FVREN=TRUE; //enable the FVR
  setup_adc(ADC_CLOCK_DIV_16|VSS_VDD);
  setup_vref(VREF_ON|VREF_ADC_2v048);  // Setup FVR
  set_adc_channel(FVR_CHANNEL); //select FVR as input channel
  delay_us(30); //needs 15uSec minimum when reading FVR
  resultResolution=read_adc(ADC_START_AND_READ);
  batteryVolt=(2.048/resultResolution)*1024;
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