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otavio_fisica
Joined: 20 Jul 2006
Posts: 29
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| Problems with ADC in the PIC16F689 |
 Posted: Sat Jul 28, 2007 9:49 pm |
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Hi...
I have some problems with the A/D converter of the PIC 16F689. The code I am using is the following:
| Code: | long int angulo;
void main()
{
setup_adc_ports(sAN0|VSS_VDD);
setup_adc(ADC_CLOCK_INTERNAL);
set_adc_channel(0);
setup_spi(SPI_SS_DISABLED);
setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1);
setup_timer_1(T1_DISABLED);
setup_comparator(NC_NC_NC_NC);
delay_us(50);
while(true){
output_high(PIN_C5); //this is just a led pin.
angulo = 0;
angulo = read_adc(); //reads the adc and then stores the result in the variable angulo
delay_ms(100);
printf("%Lu",angulo); //prints the result through the serial port.
output_low(pin_c5);
}
} |
The problem is that the ADC just doesn't seem to work. When I attach the pin AN0 to the VSS, the result should be 0 and it should be 1024 when the pin is attached to the VCC. But what I got was a 48 for when it is tied to the VSS and a crazy value in the other case.
Can you identify some problem with my code?
Any help would be of great value...
Thanks. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sat Jul 28, 2007 10:44 pm |
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1. Do you have a debugger (ICD-U40, or ICD2) connected to your board
while you are running these tests ?
2. Post all the #fuse, #device, and #use statements for your program.
3. Post your compiler version. |
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Guest
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| Here it is. |
| Posted: Sun Jul 29, 2007 7:06 am |
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Oh, sorry. My .h file is the following one.
| Code: |
#include <16F689.h>
#device adc=10
#FUSES NOWDT //No Watch Dog Timer
#FUSES XT //Crystal osc <= 4mhz
#FUSES NOPROTECT //Code not protected from reading
#FUSES NOBROWNOUT //No brownout reset
#FUSES NOMCLR //Master Clear pin used for I/O
#FUSES NOCPD //No EE protection
#FUSES NOPUT //No Power Up Timer
#FUSES NOIESO //Internal External Switch Over mode disabled
#FUSES NOFCMEN //Fail-safe clock monitor disabled
#use delay(clock=4000000)
#use rs232(baud=9600,parity=N,xmit=PIN_B7,rcv=PIN_B5,bits=8,stream=sensor) |
My compiler's version is IDE, PCB, PCM, PCH 4.032.
I thought of some problem in the serial communication, but it is ok. I made the PIC transfer integer numbers to the other one in a FOR loop, and it worked perfectly. I don't know what may be happening. |
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otavio_fisica
Joined: 20 Jul 2006
Posts: 29
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| Posted: Sun Jul 29, 2007 7:07 am |
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I also do not have a debugger in my system.
I forgot logging in in the last reply. Sorry. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Jul 29, 2007 5:29 pm |
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Do you have a programmer attached to your board ? It uses the
AN0 pin.
I don't have a 16F689, but I do have a 16F690. I installed vs. 4.032
and compiled your program for the 16F690. I added a 500 ms delay
in your loop, because your loop was too fast.
I put a 5K trimpot on pin 19 (AN0), with the end terminals connected
to +5v and to Ground. I slowly turned the pot from one end to the
other, and it worked:
| Quote: | 1023
1023
1023
902
817
787
747
699
625
559
470
362
297
238
168
81
0
0 |
If the debugger (ICD2) is attached, then I get some missing codes.
That's because the AN0 pin is used by the debugger, and the debugger
loads down the pin. (I am using the ICD2 as a programmer).
| Quote: | 1023
1022
1022
<== Note missing codes
791
618
504
434
357
161
0
0
0 |
I suggest that you try a different pin which is not used by the debugger.
Try using AN4 instead, on pin 16. Make the changes shown in bold:
| Quote: | setup_adc_ports(sAN4 | VSS_VDD);
setup_adc(ADC_CLOCK_INTERNAL);
set_adc_channel(4); |
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otavio_fisica
Joined: 20 Jul 2006
Posts: 29
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| It still does not work |
| Posted: Mon Jul 30, 2007 7:13 am |
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I do not have any ICD attached to my system. Yet I tried to change the pin, but the result was the same. After many tests, I tried the following code:
| Code: | float media,final;
int16 i, angulo, parcial;
byte ser, a, saida;
int saidera;
while(true){
angulo = 0;
for (i=1;i<=3; i++){
parcial = read_adc();
angulo = angulo + parcial;
delay_ms(200);
}
media = angulo/3;
media = 255*media;
media = media/1023;
saidera=(int8)media;
putc(saidera);
}} |
As you can see, I tried sending the value saidera. The calcullus with media were only tests. They will be different. I tried these ones just to change the scale to a int8 number that will be transmitted through the serial line. The calcullus will be different, but the result will still be a int8 number.
What I got was a 63 for when the analog channel is tied to the VCC and a 0 for when it is tied to the VSS. When it is tied to the system I want to measure, it works fine, but in this strange scale that goes from 0 to 63. According to my code, it should be from 0 to 255.
I tried many different variations of this code in the simulator, and everytime I implement the code in the hardware system, the result is the same.
I don't have any idea of what is happening. |
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otavio_fisica
Joined: 20 Jul 2006
Posts: 29
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| Posted: Mon Jul 30, 2007 7:16 am |
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Oh, I forgot... I tried to do it with that delay of 100us and then I changed to 200ms, for PCM said it was too fast. The result was the same for both the delays.
Just one more information.
Thanks for your help. |
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otavio_fisica
Joined: 20 Jul 2006
Posts: 29
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| I tried this other code |
| Posted: Mon Jul 30, 2007 9:17 am |
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I tried this other code:
| Code: | while(true){
angulo = 0;
for (i=1;i<=3; i++){
putc(i);
delay_ms(200);
parcial = read_adc();
angulo = angulo + parcial;
}
media = (float)4*angulo/3;
media = 255*media;
media = media/1023;
saidera=(int8)media;
putc(saidera);
} |
The variables are of the same type of the ones of the last post.
I tried this because I think the problem was with the convertion of the variable media to a int8 type. I think the compiler was truncating the first two bits of the variable media (which uses only 10 bits). So I tried multipling the variable angulo by 4, so that the first two bits would be 0. During the convertion, the variable saidera would store the correct value of media.
I have difficulties on sending a in16 variable through the serial port to another pic. I mean, with the other pic, I can't get the result correctly to store it in a int16 variable. That's because I want to make all the calcullations before sending the value. If I could send directly the variable angulo, after the for loop, it would also solve my problem. I think it would be a better solution. But, if there's no other possibility, I think it's fine to do what I tried now. Do you agree? Any suggestion? |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon Jul 30, 2007 12:00 pm |
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| Quote: | float media,final;
int16 i, angulo, parcial;
byte ser, a, saida;
int saidera;
while(true){
angulo = 0;
for (i=1;i<=3; i++){
parcial = read_adc();
angulo = angulo + parcial;
delay_ms(200);
}
media = angulo/3;
media = 255*media;
media = media/1023;
saidera=(int8)media;
putc(saidera);
}} |
This code is too complicated for an initial test. Your purpose is to get
the A/D to give a good output. Use the test program that I posted
earlier. Don't do this complex math now. |
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