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art
Joined: 21 May 2015
Posts: 181
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| AN1 and AN2 no output |
 Posted: Mon Oct 19, 2015 2:55 am |
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Hi, i would like to know why AN1 and AN2 result show 0. How to solve this problem?
| Code: |
#include <18F4550.h>
#DEVICE ADC=10
#fuses HS,NOWDT,NOPROTECT,NOLVP,NODEBUG,USBDIV,PLL5,CPUDIV1,VREGEN
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
main()
{
int value1,value2,value3;
setup_adc_port( AN0_TO_AN2);
setup_adc( ADC_CLOCK_INTERNAL );
while(true)
{
set_adc_channel( 0 );
value1 = Read_ADC();
delay_ms(100);
set_adc_channel( 1 );
value1 = Read_ADC();
delay_ms(100);
set_adc_channel( 2 );
value1 = Read_ADC();
delay_ms(100);
printf("\rAN0: %4i AN1: %4i AN2: %4i",value1,value2,value3);
}
} |
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alan
Joined: 12 Nov 2012
Posts: 357
Location: South Africa
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| Posted: Mon Oct 19, 2015 4:19 am |
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| Look at your code again. You declare value1 to value3 but only use value1 when reading the ADC. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon Oct 19, 2015 4:21 am |
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In addition to that:
The 18F4550 data sheet says:
| Quote: | For the A/D converter to meet its specified accuracy,
the charge holding capacitor (CHOLD) must be allowed
to fully charge to the input channel voltage level |
This means after you change the A/D channel, you must
wait for the specified acquisition time before doing an A/D
conversion. The data sheet specifies this as 2.45 usec.
Currently you have no delay after changing the A/D channels.
You need to add a delay after each channel change.
You could use delay_us(5), to be safe.
The data sheet also says:
| Quote: | The maximum recommended impedance for analog
sources is 2.5 kΩ. |
Make sure that the external circuits connected to the A/D pins
has a resistance 2.5K maximum. |
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art
Joined: 21 May 2015
Posts: 181
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| Posted: Mon Oct 19, 2015 4:48 am |
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Hi,
Sorry for typing mistake. But value2 and value3 result still 0.
| Code: |
#include <18F4550.h>
#DEVICE ADC=10
#fuses HS,NOWDT,NOPROTECT,NOLVP,NODEBUG,USBDIV,PLL5,CPUDIV1,VREGEN
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
main()
{
int value1,value2,value3;
setup_adc_port( AN0_TO_AN2);
setup_adc( ADC_CLOCK_INTERNAL );
while(true)
{
set_adc_channel( 0 );
value1 = Read_ADC();
delay_ms(100);
set_adc_channel( 1 );
value2 = Read_ADC();
delay_ms(100);
set_adc_channel( 2 );
value3 = Read_ADC();
delay_ms(100);
printf("\rAN0: %4i AN1: %4i AN2: %4i",value1,value2,value3);
}
}
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon Oct 19, 2015 4:58 am |
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Did you read my post ? What about the needed delays after you change
each ADC channel ? They are still missing from your code. |
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temtronic
Joined: 01 Jul 2010
Posts: 9221
Location: Greensville,Ontario
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| Posted: Mon Oct 19, 2015 5:19 am |
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this is wrong...
setup_adc( ADC_CLOCK_INTERNAL );
according to the datasheet it should only be used for FOsc <1MHz. You are running the PIC at 20 MHz
'INTERNAL' for all PICs is meant for 'sleep' mode operation.
And you still need the delay_us(5) after each setting of the adc channel.
Jay |
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ezflyr
Joined: 25 Oct 2010
Posts: 1019
Location: Tewksbury, MA
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| Posted: Mon Oct 19, 2015 6:15 am |
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Hi,
Why are you using '%i' in your printf statement? That is for pointers. You should use '%u' instead.
You know, CCS provides a lot of example code to demonstrate many PIC features and compiler functions. Have you looked at any of them? They are provided for a reason!
_________________
John
If it's worth doing, it's worth doing in real hardware! |
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art
Joined: 21 May 2015
Posts: 181
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| Posted: Mon Oct 19, 2015 6:26 am |
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Ok, i've add delay_us(5) after change each adc channel. What should i replace setup_adc( ADC_CLOCK_INTERNAL ) ?
| Code: |
#include <18F4550.h>
#DEVICE ADC=10
#fuses HS,NOWDT,NOPROTECT,NOLVP,NODEBUG,USBDIV,PLL5,CPUDIV1,VREGEN
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
main()
{
int value1,value2,value3;
setup_adc_port( AN0_TO_AN2);
setup_adc( ADC_CLOCK_INTERNAL );
while(true)
{
set_adc_channel( 0 );
delay_us(5)
value1 = Read_ADC();
delay_ms(100);
set_adc_channel( 1 );
delay_us(5)
value2 = Read_ADC();
delay_ms(100);
set_adc_channel( 2 );
delay_us(5)
value3 = Read_ADC();
delay_ms(100);
printf("\rAN0: %4i AN1: %4i AN2: %4i",value1,value2,value3);
}
} |
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ezflyr
Joined: 25 Oct 2010
Posts: 1019
Location: Tewksbury, MA
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| Posted: Mon Oct 19, 2015 6:37 am |
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Hi,
How about consulting the CCS manual, and studying the 'setup_adc' function?
_________________
John
If it's worth doing, it's worth doing in real hardware! |
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art
Joined: 21 May 2015
Posts: 181
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| Posted: Mon Oct 19, 2015 6:23 pm |
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Hi guys,
It works, thank you very much  |
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ezflyr
Joined: 25 Oct 2010
Posts: 1019
Location: Tewksbury, MA
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| Posted: Mon Oct 19, 2015 6:37 pm |
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Hi,
You should post your corrected code, so the next guy can benefit from this thread! Pay it forward!
_________________
John
If it's worth doing, it's worth doing in real hardware! |
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art
Joined: 21 May 2015
Posts: 181
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| Posted: Mon Oct 19, 2015 7:06 pm |
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| Code: |
#include <18F4550.h>
#DEVICE ADC=10
#fuses HS,NOWDT,NOPROTECT,NOLVP,NODEBUG,USBDIV,PLL5,CPUDIV1,VREGEN
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
main()
{
int value1,value2,value3;
setup_adc_port( AN0_TO_AN2);
setup_adc( ADC_CLOCK_INTERNAL );
while(true)
{
set_adc_channel( 0 );
delay_us(5)
value1 = Read_ADC();
delay_ms(100);
set_adc_channel( 1 );
delay_us(5)
value2 = Read_ADC();
delay_ms(100);
set_adc_channel( 2 );
delay_us(5)
value3 = Read_ADC();
delay_ms(100);
printf("\rAN0: %4u AN1: %4u AN2: %4u",value1,value2,value3);
}
} |
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art
Joined: 21 May 2015
Posts: 181
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| Posted: Mon Oct 19, 2015 7:38 pm |
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| Sorry, I have another one question, if i change setup_adc_port( AN0_TO_AN2); to setup_adc_port( AN0_TO_AN5); , but at the same time i just used only AN0 and AN1. Do I have to connect AN2, AN3, AN4 and AN5 pin to ground? |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19499
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| Posted: Tue Oct 20, 2015 12:48 am |
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_Every_ unused input, should always be connected to something.
On digital inputs, ground, or supply. Doesn't matter which. Floating digital inputs, increase the risk of spurious operation, and will increase power consumption a little. If the pin floats into the transition region of the gate for a prolonged period, it can actually reduce the life of the chip....
On analog inputs, floating ones will increase noise seen on the other inputs (they are clamped by the Vref, not the supply rails, and if a spike is clamped into this, it is seen on the other inputs).....
Remember gates contain diode structures. Electrons flowing through a pin will create current _somewhere_. Currents in unwanted parts of a chip, are a recipe for unexpected behaviour.... |
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art
Joined: 21 May 2015
Posts: 181
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| Posted: Tue Oct 20, 2015 1:11 am |
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Dear Ttelmah,
Thank you very much for your clear explanation. |
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