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weg22
Joined: 08 Jul 2005
Posts: 91
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| Help reading in an analog signal |
 Posted: Wed Nov 08, 2006 3:33 pm |
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Hi all,
I'm looking to read in an analog voltage from an infrared sensor:
http://www.acroname.com/robotics/parts/R144-GP2Y0A02YK.html
and display the digital value. I plan to hardwire the sensor output to PIN_F0 of my pic 18F8722. I've never done A/D conversion with a PIC before, so I was wondering if my code below looks okay? Also, I'm not sure how the #device adc=8 factors in??
The sensor is due in on Friday, so it's not like I can just hook it up and see if it works...trying to get the bugs ironed out beforehand :-)
| Code: |
#include <18F8722.h>
#device adc=8
#include <stdlib.h>
#include <math.h>
#fuses HS,NOWDT,NOPROTECT,PUT,NOLVP
#use delay(clock=10000000)
#use rs232(baud=9600, xmit=PIN_A4, rcv=PIN_A5, stream=PC)
#define LED PIN_A0
main()
{
int value=0;
while(1)
{
// setup to do A/D conversion on AN5
setup_adc_ports(AN0_TO_AN5);
setup_adc(ADC_CLOCK_DIV_8);
set_adc_channel(5);
delay_us(20);
value = read_adc();
setup_adc(ADC_OFF);
fprintf(PC, "IR Value: %u\r\n", value);
}
} // end of main
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Nov 08, 2006 3:59 pm |
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Look at the items shown in bold below:
| Quote: | #use rs232(baud=9600, xmit=PIN_A4, rcv=PIN_A5, stream=PC)
#define LED PIN_A0
// setup to do A/D conversion on AN5
setup_adc_ports(AN0_TO_AN5);
setup_adc(ADC_CLOCK_DIV_8);
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You're setting up AN0-AN5 as analog pins.
Here is the correspondence between the PIC pins and Analog pins,
from the 18F8722 data sheet:
| Code: |
RA0 AN0
RA1 AN1
RA2 AN2
RA3 AN3
RA5 AN4
RF0 AN5 |
But you can't specify pin RA5 as the UART rcv pin, and also configure it
as an analog pin. The same thing with the LED pin. It must be a digital
pin. You can't configure it as analog, which you are doing with the
setup_adc_ports(AN0_TO_AN5) statement. |
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weg22
Joined: 08 Jul 2005
Posts: 91
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| Posted: Wed Nov 08, 2006 5:27 pm |
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Yeah, I kinda figured that. The problem is I am using a PCB that's been made up a while back. It uses PIN_A0 as the LED pin so I can't change that. And all the other analog pins are used up except for RF0, RF2, and RF4. So I need to use one of those 3 pins as the analog but based on the 18F8722.h file, there's no way to specify this without including AN0-AN4. I guess I have to hard code this myself, but I'm not sure how?
Besides that small mistake, does everything else in the code look correct? |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Nov 08, 2006 6:29 pm |
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The 18F8722 doesn't permit the enabling/disabling of individual analog
pins. It has to be done in pre-defined groups. You probably have
to cut and jumper the board. I can't really help. |
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weg22
Joined: 08 Jul 2005
Posts: 91
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| Posted: Thu Nov 09, 2006 8:17 am |
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Oh, I thought you could come up with a workaround to that...but I guess not. So if I do decide to cut the LED from A0 and hard wire it to G0, will the code below work?
Also, what if I wanted to read an analog signal on pins A0 and A1...what else would I have to change in the code below besides the setup_adc_ports statement?
Thanks in advance,
-weg
| Code: |
#include <18F8722.h>
#device adc=8
#include <stdlib.h>
#include <math.h>
#fuses HS,NOWDT,NOPROTECT,PUT,NOLVP
#use delay(clock=10000000)
#use rs232(baud=9600, xmit=PIN_A4, rcv=PIN_A5, stream=PC)
#define LED PIN_G0
main()
{
int value=0;
while(1)
{
// setup to do A/D conversion on AN5
setup_adc_ports(AN0);
setup_adc(ADC_CLOCK_DIV_8);
set_adc_channel(0);
delay_us(20);
value = read_adc();
setup_adc(ADC_OFF);
fprintf(PC, "IR Value: %u\r\n", value);
}
} // end of main
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