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Message |
red32terra
Joined: 28 Sep 2008
Posts: 7
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| sending string/characters during zero crossing |
 Posted: Wed Dec 10, 2008 5:20 am |
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Hi.
I am sort of a newbie in this thing and I am looking for any help on putc/puts characters during zero crossing. I am using PIC16F877A.
I want to send:
| Code: |
for (Ctr1=0;Ctr1<=7;Ctr1++)
{
putc (TXBuffer[Ctr1]);
Delay_us(500);
} |
Is it recommended to put it in an external interrupt rb0, like this:
| Code: | #int_ext
void ext_isr(){
for (Ctr1=0;Ctr1<7;Ctr1++)
{
putc (TXBuffer[Ctr1]);
Delay_us(500);
}
} |
or like this
| Code: |
void Xmit_at_zerocrossing()
{
while(input(PIN_B0))
{
for (Ctr1=0;Ctr1<7;Ctr1++)
{
putc (TXBuffer[Ctr1]);
Delay_us(500);
}
}
} |
Or any another idea? If so, how can I test that I sent all TXBuffer[7] during zero crossing. Tnx for any reply. Any help would be very much appreciated. |
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SherpaDoug
Joined: 07 Sep 2003
Posts: 1640
Location: Cape Cod Mass USA
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| Posted: Wed Dec 10, 2008 7:05 am |
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Are you trying to inject serial characters onto the 60Hz (50Hz) power line when the power line is crossing zero? That is not going to be easy to decode. It would be easier at the peak of the sine wave where voltage is changing more slowly.
_________________
The search for better is endless. Instead simply find very good and get the job done. |
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red32terra
Joined: 28 Sep 2008
Posts: 7
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| Posted: Wed Dec 10, 2008 2:40 pm |
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Hi sir.
You are right. We are injecting (asynchronously) serial characters onto zero crossings of a power line (sort of a timed transmission data communication) which somehow lessen noise during transmission in the power line. Will it really be difficult to decode??? How?
There was a thesis ( http://library2.usask.ca/theses/available/etd-02162005-150411/unrestricted/akerman.pdf ) that performed this. However, he used MC68360 QUICC instead of a PIC16F877. Can I perform this using CCS and PIC16F877A??
Thank you for any reply. |
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SherpaDoug
Joined: 07 Sep 2003
Posts: 1640
Location: Cape Cod Mass USA
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| Posted: Wed Dec 10, 2008 3:07 pm |
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I didn't read the whole thesis, but reading the abstract and conclusions confirmed my suspicions.
| Code: | In the tests
conducted, the noise spikes from power supply rectifier switch-off caused the most
errors. In other environments, however, it may be found that other noise spikes can cause
additional errors, such as those caused by fluorescent lights (near the zero crossings of
the 60 Hz mains signal). |
This to me means that near the zero crossings is a particularly bad choice of times to send data. The peaks also seem a poor choice. In the paper they are continually testing and adaptively choosing their time slots for data transmission. If you want success I suggest you do the same.
_________________
The search for better is endless. Instead simply find very good and get the job done. |
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FvM
Joined: 27 Aug 2008
Posts: 2337
Location: Germany
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| Posted: Wed Dec 10, 2008 3:26 pm |
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| Zero-crossing measurement isn't difficult to my opinion. It's generally used by circuits that perform zero voltage switching or phase-control of mains powered loads. Transformer supplied circuits can sense the mains voltage polarity at the rectifier AC input, others may use an opto-coupler to acquire it at the mains terminals directly. With a hold-off time, that surpresses possible multiple triggers at the zero crossing, no additional filtering is required, usually. |
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libor
Joined: 14 Dec 2004
Posts: 288
Location: Hungary
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| Posted: Wed Dec 10, 2008 4:00 pm |
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There's an application note on Microchip for X10 powerline communication:
AN236 |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Dec 10, 2008 4:26 pm |
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CCS has a driver and example file to interface a PIC to an X10 TW523
device:
| Quote: | c:\program files\picc\examples\ex_x10.c
c:\program files\picc\drivers\x10.c |
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Douglas Kennedy
Joined: 07 Sep 2003
Posts: 755
Location: Florida
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| Posted: Wed Dec 10, 2008 5:21 pm |
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TW523 is probably the way to go. You get the transformer isolation, a power supply for the pic and a send receive module that will speak x10 to the power line.
X10 has extended commands which you could use for customizing. The zero crossing environment isn't meant for speedy communication so messages need to be short. |
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FvM
Joined: 27 Aug 2008
Posts: 2337
Location: Germany
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| Posted: Thu Dec 11, 2008 12:39 am |
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| Although the intended application has some features similar to X10 as zero crossing synchronisation, it's apparently not X10, sending full characters with FSK modulation at higher baud rate. I didn't completely understand, if the shown code is actually performing as intended, but the linked literature is clear in this respect. It reports interesting results regarding mains synchronisation effects. |
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