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dvizma
Joined: 04 Apr 2016
Posts: 3
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| All adc channels are giving same reading |
 Posted: Mon Apr 04, 2016 12:41 pm |
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I am using PIC16F887 at 16Mhz. I am using four adc channels. However readings for all the channels are same. I used the same code with pic16f688 at 12Mhz and the readings were fine. Here is the code I am using.
| Code: |
#include <16F887.H>
#device ADC=10
#use delay(clock=16000000)
#fuses HS,NOWDT,NOPROTECT,NOBROWNOUT,NOPUT
void main()
{
output_high(led1);
delay_ms(200);
output_low(led1);
printf("\nStarted");
setup_timer_1(T1_INTERNAL|T1_DIV_BY_8);
//ext_int_edge(l_to_h);
//enable_interrupts(INT_EXT);
//enable_interrupts(GLOBAL);
setup_adc(ADC_CLOCK_DIV_32);
setup_adc_ports(sAN0|sAN1|sAN2|sAN4|VSS_VREF);
while(1)
{
unsigned int16 lcdA, lcdB, lcdC, lcdD;
set_adc_channel(4);
delay_us(20);
lcdA= read_adc();
set_adc_channel(2);
delay_us(20);
lcdB= read_adc();
set_adc_channel(1);
delay_us(20);
lcdC= read_adc();
set_adc_channel(0);
delay_us(20);
lcdD= read_adc();
printf("\n%lu,%lu,%lu,%lu",lcdA,lcdB,lcdC,lcdD);
delay_ms(20);
}
}
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asmboy
Joined: 20 Nov 2007
Posts: 2128
Location: albany ny
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| Posted: Mon Apr 04, 2016 1:10 pm |
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while you did increase the master clock
i note, you did NOT change this line
| Code: |
setup_adc(ADC_CLOCK_DIV_32); |
what would be nice is if you could div_64
but for this part - you can't - tough spot to be if
you MUST have 16mhz |
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dvizma
Joined: 04 Apr 2016
Posts: 3
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| Posted: Mon Apr 04, 2016 1:20 pm |
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As per 16F887.H, adc can have only three modes
#define ADC_CLOCK_DIV_2 0x100
#define ADC_CLOCK_DIV_8 0x40
#define ADC_CLOCK_DIV_32 0x80
So I can't use divide by 64 |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19535
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| Posted: Mon Apr 04, 2016 1:31 pm |
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Fosc/32, is legal to 20MHz.
Problems:
1) the code is incomplete. Printing to serial, yet no serial setup. Doesn't give us confidence that this is 'real'.....
2) What is feeding Vref?. If this was floating you might well get the same value from each channel, as the internal diode structures would clamp the Vref to each input as it was selected,,,,,
3) What is the impedance of the analog sources. Though you say the code is the same, has the hardware changed?. |
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asmboy
Joined: 20 Nov 2007
Posts: 2128
Location: albany ny
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| Posted: Mon Apr 04, 2016 2:15 pm |
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| Quote: | | I used the same code with pic16f688 |
worries me
can you
a) POST YOUR CURRENT SCHEMATIC ??
b} what IS the value you read that never changes ??
i assume as it appears on your LCD |
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dvizma
Joined: 04 Apr 2016
Posts: 3
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| Posted: Tue Apr 05, 2016 12:22 am |
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Sorry for the incomplete code. I am actually trying to build this
https://troels.leegaard.org/misc/grundtal20047/
When I started, I didn't have PIC16F887, so I read only the four back panel values using PIC16F688
Here is the working code for 16f688
| Code: |
#include <16F688.H>
#device ADC=10
#use delay(clock=12000000)
#fuses HS,NOWDT,NOPROTECT,NOBROWNOUT,NOPUT
#use rs232(baud = 9600,parity=N,xmit =PIN_c4,rcv= PIN_c5,ERRORS)
#define panA pin_a0
#define panB pic_a1
#define panC pin_a2
#define panD pin_c0
#define led pin_c2
void main()
{
char ch;
unsigned int16 A, B, C,D;
output_high(led);
setup_adc(ADC_CLOCK_DIV_16);
printf("\nStarting");
while(1)
{
set_adc_channel(0);
delay_us(20);
A= read_adc();
set_adc_channel(1);
delay_us(20);
B= read_adc();
set_adc_channel(2);
delay_us(20);
C= read_adc();
set_adc_channel(4);
delay_us(20);
D=read_adc();
printf("\n%lu,%lu,%lu,%lu",A,B,C,D);
delay_ms(40);
}
}
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It gave me these readings
| Code: |
206,307,830,324
205,896,307,205
509,580,571,0
307,221,867,307
221,835,307,205
563,492,198,289
537,492,68,571
273,841,307,221
905,307,273,320
265,326,307,832
614,17,524,614
807,358,307,273
281,206,311,828
236,354,844,204
0,614,571,476
358,281,236,904
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As you can see only one panel has a high value at every instant.
When switching to PIC16F887 I am using the exact code below:
| Code: |
#include <16F887.H>
#device ADC=10
#use delay(clock=16000000)
#fuses HS,NOWDT,NOPROTECT,NOBROWNOUT,NOPUT
#use rs232(baud=9600, xmit=pin_c6, rcv=pin_c7, bits=8,parity=N, ERRORS)
#define panA pin_a0
#define panB pin_a1
#define panC pin_a2
#define panD pin_a4
#define led1 pin_d6
unsigned int16 lcdA, lcdB, lcdC, lcdD;
void main()
{
output_high(led1);
delay_ms(200);
output_low(led1);
printf("\nStarted");
//setup_timer_1(T1_INTERNAL|T1_DIV_BY_8);
//ext_int_edge(l_to_h);
//enable_interrupts(INT_EXT);
//enable_interrupts(GLOBAL);
setup_adc(ADC_CLOCK_DIV_32);
setup_adc_ports(sAN0|sAN1|sAN2|sAN4);
while(1)
{
set_adc_channel(4);
delay_us(20);
lcdA= read_adc();
set_adc_channel(2);
delay_us(20);
lcdB= read_adc();
set_adc_channel(1);
delay_us(20);
lcdC= read_adc();
set_adc_channel(0);
delay_us(20);
lcdD= read_adc();
printf("\n%lu,%lu,%lu,%lu",lcdA,lcdB,lcdC,lcdD);
delay_ms(30);
}
}
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The readings which I am getting are:
| Code: |
284,313,353,377
560,466,432,421
558,524,500,480
284,368,396,417
281,315,348,376
560,464,432,421
560,525,499,476
283,379,420,432
561,492,475,469
560,537,526,516
284,371,409,436
284,313,352,376
560,462,435,428
561,533,508,495
284,379,418,440
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'
I am changing the crystal to 20MHz. Let's see if it helps |
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temtronic
Joined: 01 Jul 2010
Posts: 9241
Location: Greensville,Ontario
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| Posted: Tue Apr 05, 2016 5:39 am |
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OK, silly question......
If the first PIC and code functions 100% WHY don't you set the clock for the 2nd PIC to be 12MHz, same as the first one ?
This way the pulse widths and timings will be 100% the same...
Also
Is the physical setup for the 2nd PIC the same as the 1st? Reading 8 bit analog requires good PCB layout, 10 bit or more needs GREAT PCB layout !
And...
I see all of the ADC readings are not 'solid' or 'stable'. Is the scale in an enclosed box with a known weight? Are you using shilded cables? More information about the actual measuring setup would be helpful.
Jay |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19535
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| Posted: Tue Apr 05, 2016 7:29 am |
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An obvious screaming difference.
You are leaving the ADC set at it's default port settings in the first code.
In the second you are specifying to use the VREF input. As I said at the start _what have you got connected to Vref_?..... |
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temtronic
Joined: 01 Jul 2010
Posts: 9241
Location: Greensville,Ontario
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| Posted: Tue Apr 05, 2016 8:25 am |
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I'm still trying to figure out..
where 'all the adc channels are giving the same reading ?
In neither the 'working' program or the 2nd, NONE of the data is the same for all 4 channels.
Looks like 'random' numbers.
I'd like to know more about the actual hardware setup.
Jay |
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gpsmikey
Joined: 16 Nov 2010
Posts: 588
Location: Kirkland, WA
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| Posted: Tue Apr 05, 2016 11:00 am |
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Kind of afraid to ask, but this is on real hardware right? (not Proteus)
_________________
mikey
-- you can't have too many gadgets or too much disk space !
old engineering saying: 1+1 = 3 for sufficiently large values of 1 or small values of 3 |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Apr 05, 2016 11:47 pm |
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| Quote: | I am using PIC16F887 at 16Mhz. I am using four adc channels. However readings for all the channels are same.
The readings which I am getting are:
284,313,353,377
560,466,432,421
558,524,500,480
284,368,396,417
281,315,348,376
560,464,432,421
560,525,499,476
283,379,420,432
561,492,475,469
560,537,526,516
284,371,409,436
284,313,352,376
560,462,435,428
561,533,508,495
284,379,418,440
|
Can you explain how these readings are "all the same" ? It looks to me
like they either increase or decrease as you look at each group of four
entries. They are not "all the same". |
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temtronic
Joined: 01 Jul 2010
Posts: 9241
Location: Greensville,Ontario
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| Posted: Wed Apr 06, 2016 5:20 am |
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I had a look at the link the provided and if you then go to the 'A sketch' sub-link you can see what he's trying to do.
Simply put he's trying to read a muxed 4by7seg LCD display from a scale. By decoding which segments are on or off, you can decode the actual reading.That saves reading 4 strain gauges and complicated math.....
The code the OP presents is NOT a complete 'translation' so that's one reason we are struggling with his code.The code from the link is flawed (the function digitalREAD() is not posted). What isn't known is the speed of the 'LCD reader' micro!
I recall using the 'read-the-display' cheat 20 years ago, though using LEDs back then, seemed easier no backbplane signals to deal with.
Jay |
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nailuy
Joined: 21 Sep 2010
Posts: 159
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| Posted: Mon Apr 11, 2016 1:41 pm |
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| Code: | | setup_adc_ports(sAN0|sAN1|sAN2|sAN4|VSS_VREF); |
I think problem is from here.
On data sheet you can select vref+ as AN3 or VDD.
If on your schematic this input AN3 do not have perfect stabilizer you may have this variable data.
also must have something how to select this Vref+ (AN3 or VDD).
I hope this it will help you...
Best regards. |
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