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Synchronizing flashing LEDs and RTCs

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2005-2006 » Archive through 28 March, 2006 » Synchronizing flashing LEDs and RTCs « Previous Next »

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Atferrari
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Username: Atferrari

Post Number: 155
Registered: 05-2005


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Posted on Tuesday, 14 March, 2006 - 11:42 pm:   Edit Post Delete Post Print Post

There are three independent 16F877 (eventually 16F628), (no clock sharing), monitoring three inputs each. Depending if set or clear plus other internal variables the respective LEDs will flash, stay permanently on or permanently off.

Additionally, each micro would be fitted with an RTC DS1307 for timestamping when the inputs go high.

Being the three micros in the same functional level (exactly the same software with no one being master/supervisor of the rest) and without any additional glue logic, how could I:

a - Have the required LEDs in the different modules, flashing at the same pace, even if a module (any one) is turned off?

b - Have the three RTC synchronized for a meaningful time stamping?

No one will be master of the rest and no data will be passed to anyone.

Thanks for any good idea.
Agustín Tomás - Buenos Aires - Argentina
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Obiwan
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Username: Obiwan

Post Number: 253
Registered: 12-2005

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Posted on Tuesday, 14 March, 2006 - 11:58 pm:   Edit Post Delete Post Print Post

If no data is to be passed, I don't think you can do it.

I think you have to pass something, somehow, sometime.

Because even slight differences in the clock will eventually end up in different flash times. the rate will be almost eaxctly the same. But over time the start time will start to differ.

I'm not sure what you mean by "meaningful time staping". I mean, isn't the time the same for all three?? Providing the RTC is fairly accurate? That part could be independent, and eventually, they will be off as well.

Either you'll have to reset the things based on some external stimuli, assuming they can run for a short period of time and remain in almost exact sync.

But the bit about flashing a LED based on the state of another, that requires information to be passed.
May the Force be with (most of) you.....
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Atferrari
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Username: Atferrari

Post Number: 156
Registered: 05-2005


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Posted on Thursday, 16 March, 2006 - 08:13 am:   Edit Post Delete Post Print Post

Hola Obiwan,

Each module takign care of its own inputs and LEDs; but when all flashing, doing it at the same time, synchronized.

I still try the way to get that "external stimuli" from one of the micros instead!. I think you got the point!...but I thinks that it's close to impossible.

If in the next days I can not work out any reasonable idea I'll give up.

Forget RTCs; found they are not needed for the moment.

Thanks for replying
Agustín Tomás - Buenos Aires - Argentina
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Zeitghost
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Username: Zeitghost

Post Number: 119
Registered: 01-2006

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Posted on Thursday, 16 March, 2006 - 08:53 am:   Edit Post Delete Post Print Post

If you run the three PICS off a common external clock, they'll stay synced together...

However in my application, I found it necessary to link the 3 /MCLEAR inputs so that the PICS came out of reset more or less together.

And there were still slight timing differences... which was a pain.
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Atferrari
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Username: Atferrari

Post Number: 157
Registered: 05-2005


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Posted on Thursday, 23 March, 2006 - 01:37 am:   Edit Post Delete Post Print Post

After some thinking I found that if one of them puts a 1 on the other PICs' pins they could start from there to synchronize to the first one.

I am awaitng my three modules to start the testing.
Agustín Tomás - Buenos Aires - Argentina

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