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Christophe
Joined: 10 May 2005
Posts: 323
Location: Belgium
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| disabling enabling ADC |
 Posted: Tue May 17, 2005 7:38 am |
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Hi..
it is true that the PIC comsumes less power when the ADC is disabled.
By stating this:
setup_adc_ports(AN0_AN1_AN3);
setup_adc(ADC_CLOCK_INTERNAL);
set_adc_channel( 0 );
Are you enabling the ADC (and consuming more power)?
Is it better ONLY to enable the ADC pheripheral when needed and disable when you've done using it?
About output impedance:
Vbat (0 - 5V)
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100k
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*--------------- AN0
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150k
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GND
What is the output impedance? And what should the adc setup be? (time necessary for C to be loaded with voltage is important) |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue May 17, 2005 1:39 pm |
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It depends upon what PIC you're using.
If you use a modern "Nanowatt" technology PIC, the A/D uses almost
nothing when it's turned on (but not converting).
Example:
The 16F88 running at 5v, uses a typical 3 nA when it's on, but not
converting. This number is from section 18.2 of the data sheet.
That's practically nothing. |
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cmdrdan
Joined: 08 Apr 2005
Posts: 25
Location: Washington
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| Posted: Tue May 17, 2005 6:00 pm |
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Christophe --
Your source impedance is the Thevenin equivalent resistance of the voltage divider, in this case 60k ohms. Unless you're running the part from less than 5 volts, the voltage divider isn't necessary.... |
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Christophe
Joined: 10 May 2005
Posts: 323
Location: Belgium
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| Posted: Wed May 18, 2005 1:13 am |
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Well I am using PIC16LF877A @3V (Vdd)
So is that using nanowatt technology?
PIC16LF87XA — 90 — μA
How can you turn the interface on and off?
do_adc {
put_on (adc) //how?
...
put_off (adc) // how?
return (..)
}
My settings are:
setup_adc_ports(AN0_AN1_AN3);
setup_adc(ADC_CLOCK_INTERNAL);
I only use AN0 and AN1 as analog inputs; with these settings AN3 is also an analog input; and I want to use it as a digital input..
Last edited by Christophe on Wed May 18, 2005 1:39 am; edited 1 time in total |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed May 18, 2005 1:38 am |
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| Quote: | Well I am using PIC16LF877A @3V (Vdd)
So is that using nanowatt technology? |
No. If it's nanowatt, it will say so on the first page of the data sheet.
Like this:
| Quote: | PIC16F87/88
Data Sheet
18/20/28-Pin Enhanced Flash
Microcontrollers with
nanoWatt Technology |
| Quote: | | How can you turn the interface on and off? |
Look in the CCS manual. The section on the setup_adc() function
says this:
| Quote: | Some typical options include:
• ADC_OFF
• ADC_CLOCK_INTERNAL
• ADC_CLOCK_DIV_32 |
So, to turn it on, you do this:
| Code: | | setup_adc(ADC_CLOCK_DIV_32); |
To turn it off you do this:
| Code: | | setup_adc(ADC_OFF); |
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Christophe
Joined: 10 May 2005
Posts: 323
Location: Belgium
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| Posted: Wed May 18, 2005 1:40 am |
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Thank you very much,
so when it's off, I can use the pins again as digital i/o ?
edit:
by stating this:
setup_adc_ports(AN0_AN1_AN3);
and the ADC is off, can I use A0 A1 and A3 as digital i/o ? |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed May 18, 2005 2:04 am |
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| Quote: |
so when it's off, I can use the pins again as digital i/o ?
setup_adc_ports(AN0_AN1_AN3); |
No. That statement configures AN0, 1, and 3 as analog.
You have to configure them as digital with this statement:
setup_adc_ports(NO_ANALOGS); |
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Christophe
Joined: 10 May 2005
Posts: 323
Location: Belgium
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| Posted: Wed May 18, 2005 2:36 am |
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PCM,
can you confirm the following code:
| Code: |
//****************************************************************************//
//Meten Adapterspanning
//Vadap = (82+150)/150*waarde*3/255
int8 meet_Vadap()
{
int8 waarde = 0;
if (!input(POWER_GOOD))
{
setup_adc_ports(AN0_AN1_AN3);
setup_adc(ADC_CLOCK_DIV_32);
set_adc_channel( 1 );
delay_us(5);
waarde = read_adc();
setup_adc(ADC_OFF);
setup_adc_ports(NO_ANALOGS);
return waarde;
}
else
{
waarde = 0;
return waarde;
}
}
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thank you
edit: seems to be not working;
after setup_adc_ports(NO_ANALOGS);
How is the A-port set up? (by means the power-good pin)
edit: I solved the problem; after setup_adc_ports(NO_ANALOGS); you HAVE to reset your pins as inputs.. |
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