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ADAM75
Joined: 16 Apr 2009
Posts: 6
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| signal alternative |
 Posted: Tue Apr 21, 2009 2:58 am |
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my problem is that I have a alternative signal between
(0 and 5) volts and a frequency of 50hz and I want to convert it into digital signals by the pic 16F877 via a serial link rs 232 but when I retrieve it I see my signal random points on the visual terminal exp: 2.5 0.5 3.85 3.2 1.25 4.36 ...........
while I wish that my signal shows 2.5 2.8 3.2 3.6 3.8 4.2 4.5 4.8 4.3 3.9 3.8 ..........
Here is my program
| Code: | #include "C:----------------------------------------------------------"
float courant;
void main()
{
setup_adc_ports(AN0);
setup_adc(ADC_CLOCK_DIV_32);
set_adc_channel(0);
delay_us(20);
while(true)
{
courant=read_adc();
courant = (courant*5)/1023;
printf("courant=%f\r",courant);
}
// TODO: USER CODE!!
} |
where is the problem if you enjoy |
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SherpaDoug
Joined: 07 Sep 2003
Posts: 1640
Location: Cape Cod Mass USA
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| Posted: Tue Apr 21, 2009 7:01 am |
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Can you accurately measure a DC source? Try a 1.5V alkaline cell or a 3V mercury cell. That would remove questions of timing.
Just what does your signal look like? Is it DC with a small AC ripple?
_________________
The search for better is endless. Instead simply find very good and get the job done. |
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Ttelmah
Guest
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| Posted: Tue Apr 21, 2009 7:22 am |
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What is your serial baud rate?.
The main limitation on the loop time for the PIC here, will be the time taken to send the data. You are sending potentially perhaps 13 characters each time round the loop. If you are running at 9600bps, then this will take nearly 14mSec. Add the time for the floating point arithmetic (depends on the processor clock, but probably at least another couple of mSec to perform both the original arithmetic, and the divisions needed to print the data), and you will only be taking perhaps 60 samples per second. What you have is exactly what you'd expect if sampling a 50Hz AC waveform, at such a slow interval....
Best Wishes |
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ADAM75
Joined: 16 Apr 2009
Posts: 6
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| signal alternative |
| Posted: Tue Apr 21, 2009 11:50 am |
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| then it is just after the program I cried[/img] |
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asmboy
Joined: 20 Nov 2007
Posts: 2128
Location: albany ny
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| Posted: Tue Apr 21, 2009 4:37 pm |
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a factor that is missing here:
What is the GOAL?
1- a good running average value ?
2- OR an instantaneous value / digitized stream where the samples you collect represent the ac waveform?
3- something else entirely?
#1 can be done with external R-C , or integration as we like to call it.
#2 requires understanding of a HOST of timing issues that you have not begun to get at, and that Tlemah is kindly alluding to in the most gentle of ways.
#3 is blue sky and might be part hardware - might be a higher clock speed pic - or some hardware hybrid design.
presenting us with a clearer goal, the feedback can be more specific and better directed. |
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