Internal Voltage Reference_Solved!

[Dmitry Maximenko]

Hi!
I wonder, can we use the internal voltage reference for AD conversion for more precision?
For ex.16f1827 have Fixed Voltage Reference (FVR) with 1.024V, 2.048V and 4.096V
I would prefer 2.048V in my project.
In flowcode v4.5 Vref option for ADC are just VDD and VREF+. Is internal Voltage Reference not supported then?
How can we solve it?
Very grateful!

[Jan Lichtenbelt]

Dear Dmitry

In the datasheet of 16F1827 you see the reference voltage can be used for ADC. The register FVRCON has to be set to 0x82 (8 for FVR enabled and 2 for 2.048 V for ADC)
You can realise this with the C-code:
fvrcon= 0x82;

And set ADC to the Vref+ with 205 x 10 mV reference voltage.

Good Luck

Jan Lichtenbelt

PS: Mind the ADC error in the 16F1827
http://www.matrixmultimedia.com/mmforum ... =29&t=8746

[Dmitry Maximenko]

Hello Jan! Thank you and I have more questions:-) hope it´s ok.
If we look in a data sheet side 136 for pic16f1827:
-----------------------------------
14.3FVR Control Registers
bit 7 FVREN: Fixed Voltage Reference Enable bit
0 =Fixed Voltage Reference is disabled
1 =Fixed Voltage Reference is enabled
bit 6 FVRRDY: Fixed Voltage Reference Ready Flag bit
0 =Fixed Voltage Reference output is not ready or not enabled
1 =Fixed Voltage Reference output is ready for use
bit 5-4 Reserved: Read as ‘0’. Maintain these bits clear.
bit 3-2 CDAFVR<1:0>: Comparator and DAC Fixed Voltage Reference Selection bit
00 =Comparator and DAC Fixed Voltage Reference Peripheral output is off.
01 =Comparator and DAC Fixed Voltage Reference Peripheral output is 1x (1.024V)
10 =Comparator and DAC Fixed Voltage Reference Peripheral output is 2x (2.048V)
11 =Comparator and DAC Fixed Voltage Reference Peripheral output is 4x (4.096V)
bit 1-0 ADFVR<1:0>: ADC Fixed Voltage Reference Selection bit
00 =ADC Fixed Voltage Reference Peripheral output is off.
01 =ADC Fixed Voltage Reference Peripheral output is 1x (1.024V)
10 =ADC Fixed Voltage Reference Peripheral output is 2x (2.048V)
11 =ADC Fixed Voltage Reference Peripheral output is 4x (4.096V)

-----------------------
1)How did you get 0x82?
If I convert hex to bin :82= 10000010

2)for (4.096V)then 10000011= fvrcon= 0x83; ?
And set ADC to the Vref+ with ??? mV reference voltage for best resolution?.
I suppose that if I have 5 volts on vdd for my PIC then it better to use 4.096 volt fixed for best resolution and precision, right?
How about bit 6 FVRRDY? shall we leave it 0. (0= Voltage Reference output is not ready or not enabled)

3)Can I place C code box(fvrcon= 0x82;) for activating of internal reference in the beginning of program?
Thank you for help!
Best Regards

[Jan Lichtenbelt]

Hi Dmitry,

1) With 0x82 or bin 1000 0010 FVREN bit7=1 and ADFVR<1:0> = 10 or ref. voltage is 2.048 Volt. I choose FVRRDY bit6=0 in the case you do not need the reference voltage on the output.
2) Indeed 4.096 Volt is 0x83. For the rest I'm not a ADC specialist. Perhaps someone else can help you, or you try the different options yourself!

3) Indeed you can put the C-code at the beginning of the program, before you use the ADC.

Succes

Jan lichtenbelt

[Dmitry Maximenko]

Hi Jan,
I tried with fvrcon= 0x83; for 4.096V internal v.r.
And I changed in Vref Option to VREF+; Vref Voltage 401x10mV
Measurement became unstable. It jumped up and down. It felt like the PIC used the VREF pins that were not connected to anything and not to the Internal Voltage Reference. I have written C code in the c code box where I wrote the setting for the oscillator. (osccon = 0x68;
fvrcon= 0x83; ) What do you think, what could it be?

Thank you!

[Jan Lichtenbelt]

Hi Dmitry,

Upload your flowcode file, so the Forum can help you.
And did you look at:
http://www.matrixmultimedia.com/mmforum ... =29&t=8746

Jan

[Dmitry Maximenko]

Hi people,
Jan,thank you, I looked at the link you told about.
I have uploaded my FCD file with configuration for internal Voltage reference that not worked.
I tried to activate 4.096 volt internal voltage ref in C code as you recommended but unfortunately it does´t work:-(
I have added the file for PIC16F1827 for ADC stability so it worked nice when I use VDD+ as reference.
Please advice what to do to get Internal Voltage Reference to work.
Thank you!

[Jan Lichtenbelt]

Hi Dmitry,

If you use an external oscillator, delete osccon. If you like to use the internal oscillator, you should set the SCS<1:0> enable bits of the osccon register to 10. That means osccon = 0x6A; should be used in stead of osccon = 0x68;


Kind regards

Jan

[Dmitry Maximenko]

HI,
Yes I use internal oscillator 4 MHz.
Please, someone who can, advise what to do with internal voltage reference. It doesn´t work yet.
Thank you!

[Benj]

Hello,

Here is an updated ADC file with code to hard code in the FVR as the +VREF signal.

PIC_ADC_23.c

(8.18 KiB) Downloaded 468 times

You will also need the line of C code near the start of your program to set up the FVR.

E.G.

Code: Select all

fvrcon= 0x83;

[Dmitry Maximenko]

HI Benjamin!

Power voltage for PIC16f1827 is 5 volt in my project.
What about Vref Voltage xxx x10mV parameter for A/D Properties?
If i use 4.096 Volt internal voltage, should it be 401 x10mV ? Or it does n´t meter what is xxx?

Thank you for reply!
Best Regards

[Benj]

Hello,

The Vref voltage in the component properties simply controls how the ReadAsVoltage and ReadAsFloat macros scale the incoming data to give you back a meaningful reading.

4.096V would be 409 or 410 in the component properties depending on which way you want to do it.

[Dmitry Maximenko]

Thanks for all answers, now it works!

[Creative25]

Hi.
I am trying to use FVR wit a pic 16F1939 using Flowcode5
However it just gives me random numbers

osccon=0x7A;
fvrcon= 0x82;

On the ADC properties I use Vref+ 205 X 10
Pin number 5 is also used for The LCD Display.
If I use VDD as a reverence voltage it works fine.

What could be the Problem?

Uli

[Dmitry Maximenko]

Hi,
It can be problem with ADC file in flow (for 16f1827is PIC_ADC_23.c). I have got new one from Benj.
Best Regards
Dmitry

[Creative25]

Hi,
It can be problem with ADC file in flow (for 16f1827is PIC_ADC_23.c). I have got new one from Benj.
Best Regards
Dmitry

Does this file also work for the Pic 16F1939?
Uli

[Dmitry Maximenko]

No, I don´t think so. This file is for 16f1827. Please ask Benj on Flow forum. He answered me before.
He will surely respond by Monday. The guys are fast!
Best Regards
Dmitry

[Benj]

Hello,

This modified v5 CAL file should work with the 16F1939 device to use the internal VREF. A backup of the original CAL file should be made in case you need to use the same device or a similar device using the ADC normal settings.

The file should be placed into the following directory.
C:\Program Files\Flowcode\v5\CAL\PIC
or
C:\Program Files (x86)\Flowcode\v5\CAL\PIC

[Creative25]

Thanks for your Reply
At the moment I was intending use internal reference on only one ADC
Because on the other channels I want to have a higher Reference voltage.
Is it possible to have different reference voltages on different ADC channels?
Say 2048 on one and 4096 on the other? Do i have to enter the corresponding C code in front of each Adc Reading Macro?
Best regards:
Uli

[Benj]

Hello Uli,

If you look at line 2155 of the updated component C file I sent you then you will see the following code.

Code: Select all

//Assign FVR functionality
st_bit(adcon1, ADPREF1);
st_bit(adcon1, ADPREF0);

If you change this to look like this,

Code: Select all

//Assign FVR functionality
if (FCV_ADCVAR & 0x02)
 st_bit(adcon1, ADPREF1);
else
 cr_bit(adcon1, ADPREF1);
if (FCV_ADCVAR & 0x01)
 st_bit(adcon1, ADPREF0);
else
 cr_bit(adcon1, ADPREF0);

And then create a byte variable in your program called adcvar then you can assign the two ADPREF bits to the lower two bits of your Flowcode variable. Make sure the variable is setup correctly before you call the ADC sample routine and it will use the reference as specified by your adcvar variable.

[Creative25]

Hi Benj
Thanks for your reply
It is a bit too difficult for me to understand.
"then you can assign the two ADPREF bits to the lower two bits of your Flowcode variable"
I don understand at all because I only know Flowcode
Could you explain?

I filled in the code you Posted,
Also I created the variable but I do not know how to set the preferred reference voltage for each ADC.
I made an example program for reading the ADC where I would like to have a reference voltage of 1.024 on ADC(0)
And a reference voltage of 2.048 on ADC(1)
Could you fill in the missing parts?

Best Regards:
Uli

[Creative25]

Hi
Can someone explain what this Line Means?
if (FCV_ADCVAR & 0x02)
Does it mean "if (flowcode variable) adcvar=0X02" ?

Best Regards
Uli

[Creative25]

I have still not been able to figure out this one.
I have tried with a calculation before the ADC Macros "adcvar=0x02" and "adcvar=0x01" but it does not work
Also I tried to put the same C code in front of the ADC macros, this gives an error message.

Best Regards:
Uli

[Benj]

Hello Uli,

if (FCV_ADCVAR & 0x02)

The line above ands the value 2 or 0x02 or 0b00000010 with the variable adcvar. If the bit is set then the if statement will return true and the line underneath will be called.

It looks like you need to assign the correct +vref functionality in the ADC which was done previously and then configure the reference voltage before you start your ADC sample.

[Creative25]

Hi Benj
I finally made some progress.
I used the original PIC_CAL_ADC.c file as described.
Before each ADC is used the following c code: "fvrcon=0x83;" for 4.098 volt and "fvrcon=0x82;" for 2.048 volts
It works fine. (see attachment)
(I also tried "fvrcon=0x81;" for 1.024 volt but this did not work well, the readings become unstable. Also the datasheet for the Pic16F1939 does not state that you can use 1.024 for fvr as a reverence voltage, it only mentions 4.098 and 2.048)
This way I can change the Internal voltage reference and it gives good results, is this a good way of doing it?

Best Regards:
Uli