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'[PIC]: Acurate time interval and help with shift i'
2001\01\06@204120 by Peter May

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I noticed a posting just recently re a 1 second time interval. I need to a
very acurate 1 second interval to output data via a serial pin at 1 second
intervals. I was wondering if I would be say better to develope an external
timer with a 1 second pulse to run an interupt?

Secondly. I want to write details to an eprom (different project) and have
it recall it at a later stage. It's a weather station I am building for my
self as a learning tool. I want to store the figures like time, temp, wind
direction in degrees, etc etc etc.

I have no idea how to do this and see things like shift in shift out
mentioned everywhere but do not actually understand what all this is. Are
there any good examples on how to do this out there anywhere? Also given the
above example how do I figure out how many bytes each reading would take up
and therefore how many readings I can store?

Thanks.

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2001\01\07@013345 by Peter May

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I noticed a posting just recently re a 1 second time interval. I need to a
very acurate 1 second interval to output data via a serial pin at 1 second
intervals. I was wondering if I would be say better to develope an external
timer with a 1 second pulse to run an interupt?

Secondly. I want to write details to an eprom (different project) and have
it recall it at a later stage. It's a weather station I am building for my
self as a learning tool. I want to store the figures like time, temp, wind
direction in degrees, etc etc etc.

I have no idea how to do this and see things like shift in shift out
mentioned everywhere but do not actually understand what all this is. Are
there any good examples on how to do this out there anywhere? Also given the
above example how do I figure out how many bytes each reading would take up
and therefore how many readings I can store?

Thanks.

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2001\01\07@021428 by Roman Black

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Peter May wrote:
>
> I noticed a posting just recently re a 1 second time interval. I need to a
> very acurate 1 second interval to output data via a serial pin at 1 second
> intervals. I was wondering if I would be say better to develope an external
> timer with a 1 second pulse to run an interupt?

Hi, try using a crystal in a freq that gives division
into even seconds, then use the interrupt on timer0
to give you accurate ints at 1 second or smaller.
This is covered well in the piclist archives I believe
but I haven't done it myself.


{Quote hidden}

You will probably need to learn the I2C serial
system, used by the most common and best value
eeprom chips. The way I tackled this was to
download and print out the 24AA256 (32k x8)
eeprom datasheet by Microchip. It tells about
the eeprom chip, and gives probably the simplest
and clearest explanation of exactly what I2C
does and what the commands make that chip do.
Many other I2C info sources focus on ALL the
master/slave combinations and it can get very
hard to understand. :o)

Once you fully understand what you need to
send to the chip to make it work it is easy,
or you can make it hard by learning ALL about
I2C. ;o)
-Roman

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2001\01\07@080724 by Bob Ammerman

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You really shouldn't need any external clocking to time a 1 second interval,
unless you want to use a clock derived from the AC mains.

What kind of accuracy do you need?

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

{Original Message removed}

2001\01\07@084907 by Chris Carr

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It depends on what you mean by accurate. I use the 1 second output of
a GPS receiver as a cheap off-the-shelf source. Depending upon your location
the VLF Time Signals offer an even cheaper source but normally require some
work either building a receiver or adapting a Radio Clock.

Long Term accuracy of both is to Atomic Standards but beware the
instantaneous accuracy might be out by as much as +-50nS on GPS. The
instantaneous accuracy of VLF signals depends upon your location with
respect to the transmitting station.

Regards
Chris

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2001\01\07@090252 by Chris Carr

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It depends on what you mean by accurate. I use the 1 second output of
a GPS receiver as a cheap off-the-shelf source. Depending upon your
location
the VLF Time Signals offer an even cheaper source but normally require some
work either building a receiver or adapting a Radio Clock.

Long Term accuracy of both is to Atomic Standards but beware the
instantaneous accuracy might be out by as much as +-50nS on GPS. The
instantaneous accuracy of VLF signals depends upon your location with
respect to the transmitting station.

Regards
Chris
>

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