Searching \ for 'Long, accurate times...' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: piclist.com/techref/timers.htm?key=time
Search entire site for: 'Long, accurate times...'.

Truncated match.
PICList Thread
'Long, accurate times...'
1999\06\07@230817 by Jonathan Newport

flavicon
face
   Ok, I was wondering how I could get a long (1 second, for example)
accurate time interval without using a RTCC.  Would a 555 timer do the trick
putting it in astable mode and simply waiting for it to fire?  what about
decreasing the PIC clock speed?  Any suggestions?  Thanks...

J Newport

1999\06\08@102642 by Sam Laur

flavicon
face
>     Ok, I was wondering how I could get a long (1 second, for example)
> accurate time interval without using a RTCC.  Would a 555 timer do the trick
> putting it in astable mode and simply waiting for it to fire?  what about
> decreasing the PIC clock speed?  Any suggestions?  Thanks...

Sure, just grab yourself a watch crystal (32.768 kHz) and set the timer
prescale at 1/32. After that, just let the 8-bit timer overflow on its own,
if you're using a midrange PIC you'll have to enable timer interrupts, and
you'll be getting one once a second. If you need to time an event to be
exactly 1 second long, then clear the timer and enable the timer interrupt.
When interrupt occurs, 1 second has passed, do whatever you like :)

I just made myself a clock, with a 16F84, a 32.768 kHz crystal and a 4-digit
LED display, the old kind with bubble lenses and all :) Only took a couple
of hours, most of which was spent soldering it together. And like watch
crystals do, it's not really accurate - it lags something like 5-10 seconds
per day. And if I run it at 3V, it doesn't start oscillating immediately
when powered up - it might take anything up to 10 seconds. But then the
part isn't a 16LF84...

1999\06\08@110831 by Sean Breheny

face picon face
You can also use simple loops (as long as you don't need to be doing much
during the long time interval). For a (non-exhaustive) explanation of
several ways to get log,accurate loops, see my page on the subject:

http://www.people.cornell.edu/pages/shb7/lop.html

Sean


At 05:29 PM 6/8/99 +0300, you wrote:
>>     Ok, I was wondering how I could get a long (1 second, for example)
>> accurate time interval without using a RTCC.  Would a 555 timer do the
trick
{Quote hidden}

| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
spam_OUTshb7TakeThisOuTspamcornell.edu ICQ #: 3329174
________________________________________________________
NetZero - We believe in a FREE Internet.  Shouldn't you?
Get your FREE Internet Access and Email at
http://www.netzero.net/download/index.html

1999\06\08@112258 by Wagner Lipnharski

picon face
Does anyone already did any research about what is more accurate to get
1Hz division; the 60Hz power line frequency or a cheap 32768Hz crystal?
The fast answer could lead to the crystal, but it could not be the
truth.  I have an "old red led display table clock" that steals clock
from the 60Hz power, I never needed to adjust its timming error (it was
never noticed) except for day-light-savings adjustments.  Dallas RTC
DS-1644 has almost one minute/month error with an internal crystal.

--------------------------------------------------------
Wagner Lipnharski - UST Research Inc. - Orlando, Florida
Forum and microcontroller web site:  http://www.ustr.net
Microcontrollers Survey:  http://www.ustr.net/tellme.htm

1999\06\08@114159 by Andres Tarzia

flavicon
face
The long-term frequency stability of the power line is excellent, much
better than a 32KHz crystal.

Now, if you are going to compare with a temperature compensated crystal
(like Dallas' DS32Khz part with accuracy of +/- 1 minute per year at 0¡C to
40¡C) the answer is "I don't know". :)

I think that the better design would be something that works off the power
line but has a battery backup, along with a 32Khz crystal oscillator for the
brief periods when the power goes off.

Regards,
Andres Tarzia
Technology Consultant, SMART S.A.
e-mail: .....atarziaKILLspamspam@spam@smart.com.ar

PS: If you want ABSOLUTE accuracy, get a GPS receiver and read the time from
there.

{Original Message removed}

1999\06\08@114544 by eplus1

flavicon
face
part 0 1276 bytes
James Newton, Electronic Forms Plus,
eplus1spamKILLspamsan.rr.com <.....eplus1KILLspamspam.....san.rr.com>  1-619-674-9736 phone
1-619-674-9763 fax



> {Original Message removed}

1999\06\08@121717 by Dave VanHorn

flavicon
face
> Does anyone already did any research about what is more accurate to get
> 1Hz division; the 60Hz power line frequency or a cheap 32768Hz crystal?
> The fast answer could lead to the crystal, but it could not be the
> truth.  I have an "old red led display table clock" that steals clock
> from the 60Hz power, I never needed to adjust its timming error (it was
> never noticed) except for day-light-savings adjustments.  Dallas RTC
> DS-1644 has almost one minute/month error with an internal crystal.


You won't see any long-term problems on the power line other than missing
cycles.
They adjust the power frequency to keep in sync with atomic clocks. It used
to be done manually, a very fine vernier, it's probably now under computer
control. For the best of all worlds, use your own osc or internal counter,
and re-sync to the power line periodically.

1999\06\08@154000 by Eric Oliver

flavicon
face
Wagner,

I remember reading in a newsgroup one time ( there was a long thread about
the US power grid, etc. ). I remember that someone said that the power
companies track the frequency and periodically compensate to keep the
average at 60hz. If this is true, it would seem that the power line
frequency is more accurate over some arbitrary period.  Would be interested
to know if it is indeed true.

Eric

On Tuesday, June 08, 1999 10:23 AM, Wagner Lipnharski
[SMTP:EraseMEwagnerlspam_OUTspamTakeThisOuTEARTHLINK.NET] wrote:
{Quote hidden}

1999\06\08@154412 by Richard Martin

picon face
Wagner:
I think the U.S. power grid allows local phase changes and
adjusts the '60hz' speed once a day to get the right number
of seconds per day. At least it was 'once a day' some time ago
when I learned this. This means that no particular interval
can be trusted, and only one 24hr interval. IF you know when they
fix it.

The local 'atomic clock' is the time signal on a national TV feed.
There was an article in a 'hobby' mag (maybe Popular Electronics)
that gave a super accurate clock based on this. Or use WWV,
<but we already have 'receivers' for tv>

Dick M.

1999\06\08@162213 by Bob Drzyzgula

flavicon
face
60Hz AC will likely be more long-term accurate, while the
32KHz crystal will probably be more precise. The 32KHz
crystal will probably also have a somewhat more predictable
error function and you can likely calibrate your device
to adjust for some major portion of the error. If you can
monitor both signals, you could probably arrive at a quite
good time base, especially after a few days of calibration.

If you can interface to a SW receiver, of course you
can use WWV; NIST suggests that the recieved accuracy
is about 0.1 ppm for frequency and 1 ms for timing.

--Bob

On Tue, Jun 08, 1999 at 11:22:58AM -0400, Wagner Lipnharski wrote:
{Quote hidden}

--
============================================================
Bob Drzyzgula                             It's not a problem
bobspamspam_OUTdrzyzgula.org                until something bad happens
============================================================

1999\06\08@190701 by Reginald Neale

flavicon
face
>Does anyone already did any research about what is more accurate to get
>1Hz division; the 60Hz power line frequency or a cheap 32768Hz crystal?
>The fast answer could lead to the crystal, but it could not be the
>truth.  I have an "old red led display table clock" that steals clock
>from the 60Hz power, I never needed to adjust its timming error (it was
>never noticed) except for day-light-savings adjustments.  Dallas RTC
>DS-1644 has almost one minute/month error with an internal crystal.
>

 Wagner:

 It all depends on your time scale. If it's on the order of seconds,
 the crystal is probably better. If it's on the order of days, the
 power line is probably better. If it's in between, more info is needed.

 Measuring the accuracy of the power line over time is like measuring
 the accuracy of your car's position over the length of a trip. If
 you're only going a couple of miles, At any one time your position
 could deviate from the desired position by a few yards. If you're
 only going a couple of miles, the percentage accuracy is not great.
 If you're driving across the country, a couple of yards at your final
 destination is still pretty good accuracy. With care, your final
 position could be within a few ppm of the desired one.

 Regards,
 Reg Neale

1999\06\08@192557 by Jonathan Newport

flavicon
face
   Thanks for all your responses, I just happen to have a watch crystal, so
I may try that out...anyways, I am working on an autonomous data acquisition
device which derived its period from the on board timer.  But it seemed when
I was taking many samples (100samps/sec 3000samples), I would only get about
25seconds of sampling instead of the 30 that I should be getting.  should
the error be this large?  Maybe I'll go through my code again...I was also
thinking about using it for an exposure timer for my camera that has a
remote switch input....thought you might like to know....anyways, thanks
again...

Jonathan Newport



{Original Message removed}

1999\06\08@210005 by Nick Taylor

picon face
Hello All - -

If you want "really accurate" time, Radio Shack and Oregon Scientific
both have clocks which self synch with WWVB one or more times daily.
Either clock is about US$30.

Here is a link to one attempt to hack the R.S. clock:
    http://www.bldrdoc.gov/timefreq/index.html

- - - Nick - - -

1999\06\08@212337 by Lynx {Glenn Jones}

flavicon
face
Why is this done? I mean why does the power line need to be EXACTLY 60Hz?

------------------------------------------------------------------------------
A member of the PI-100 Club:
3.1415926535897932384626433832795028841971693993751
058209749445923078164062862089986280348253421170679

On Tue, 8 Jun 1999, Dave VanHorn wrote:

{Quote hidden}

1999\06\08@214243 by Nick Taylor

picon face
Lynx {Glenn Jones} wrote:
<snip>
> Why is this done? I mean why does the power line need to be EXACTLY 60Hz?


So that your alarm clock will buzz at the right time!

- - - Nick - - -

1999\06\09@030727 by Eric Smith

flavicon
face
Nick wrote:
> Here is a link to one attempt to hack the R.S. clock:
>      http://www.bldrdoc.gov/timefreq/index.html

No, that's the NIST page.  Useful, but no info on R.S. clocks.

1999\06\09@055758 by Sebastián Dols

flavicon
face
Subject: Re: Long, accurate times...
---
Well, and what about clocking via the power lines here in Europe, where the
line frequency is 50 Hz?. I think this makes the whole approach unusable,
because the 120% freq-conversion-factor is securely a new error source.

Only as a comment, you know.

Keep on PICing

/S

1999\06\09@074105 by Nigel Orr

flavicon
face
At 11:22 08/06/99 -0400, you wrote:
>Does anyone already did any research about what is more accurate to get
>1Hz division; the 60Hz power line frequency or a cheap 32768Hz crystal?

Short term, the crystal, long term, the line (at least in the UK).  AIUI,
the power companies can easily 'count' the number of cycles that have been
generated, and compare that to a very accurate clock, so in the long term,
the number of cycles will be exactly 50 per second.  However, there is a
permitted variation (short term) of about 5%(?).

>DS-1644 has almost one minute/month error with an internal crystal.

Most digital watches claim accuracy within +/- 15s/month.  That is about
+/-6ppm.  1 minute per month would be about 23ppm, which is far from
unreasonable for a crystal spec.

Nigel

1999\06\09@075058 by Michael Rigby-Jones

flavicon
face
Which is why appliances that use the mains frequency as a timebase always
specify 50 or 60Hz for operation.
If wouldn't be very hard to code a clock that could use either frequency
though.  In fact a PIC could detect the frequency by using a simple software
counter and adapt the timebase parameters to suit.

Regards

Mike Rigby-Jones

> {Original Message removed}

1999\06\09@103611 by Nick Taylor

picon face
Eric Smith wrote:
>
> Nick wrote:
> > Here is a link to one attempt to hack the R.S. clock:
> >      http://www.bldrdoc.gov/timefreq/index.html
>
> No, that's the NIST page.  Useful, but no info on R.S. clocks.

Here is the correct link to the R.S. clock hack:
    http://psn.quake.net/wwvbsdr.html

1999\06\09@114031 by Wagner Lipnharski

picon face
I wonder how the power grid keeps phase sync adjusting the frequency, or
worst, the phase, between each other power plant only few times a day.
In Brazil they have a huge power grid "on very tied sync" at the south,
including the world largest hydroelectric Itaipœ plant. One plant can
not have its phase out of sync, or the grid starts to fall down and a
complete blackout happens. I am not an expert on this, so I may be wrong
about how they do it.
Wagner.

Dave VanHorn wrote:
{Quote hidden}

1999\06\09@172257 by Nigel Goodwin

flavicon
picon face
In message <@spam@01BEB1BA.C6E914F0.ericKILLspamspamkedcoent.com>, Eric Oliver
<KILLspamericKILLspamspamKEDCOENT.COM> writes
>Wagner,
>
>I remember reading in a newsgroup one time ( there was a long thread about
>the US power grid, etc. ). I remember that someone said that the power
>companies track the frequency and periodically compensate to keep the
>average at 60hz. If this is true, it would seem that the power line
>frequency is more accurate over some arbitrary period.  Would be interested
>to know if it is indeed true.

I presume the USA is the same, but in the UK the mains frequency is
extremely accurate - in the long term!. It's ideal for mains driven
clocks as it's regularly corrected - years ago they used to have a large
analogue clock in power stations that had two hands, one fed from the
mains frequency, the other from an accurate source (in the UK probably
the Atomic clock at Rugby). They would adjust the frequency at midnight
to make the two hands line up, thus correcting any slight errors which
may have occurred during the day.

I presume it's not perhaps so crude these days, and most probably
completely automatic?.
--

Nigel.

       /--------------------------------------------------------------\
       | Nigel Goodwin   | Internet : RemoveMEnigelgTakeThisOuTspamlpilsley.demon.co.uk     |
       | Lower Pilsley   | Web Page : http://www.lpilsley.demon.co.uk |
       | Chesterfield    | Official site for Shin Ki and New Spirit   |
       | England         |                 Ju Jitsu                   |
       \--------------------------------------------------------------/

More... (looser matching)
- Last day of these posts
- In 1999 , 2000 only
- Today
- New search...