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'[OT]: Re: [PIC] Timer Tribulations'
2001\02\22@165102 by Tony Nixon

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Vasile Surducan wrote:
>
> On Wed, 21 Feb 2001, Tony Nixon wrote:
>
> > You will find that the clock will drift one way or the other depending
> > on temperature, so using the mains as a frequency source is much more
> > accurate.
>
>   You are certainly joking ! Or in your country mains frequency drift is
> under 0.5% ...
>
>   Vasile
>


Perhaps a bit of AC math about power consumption in a system as large as
a state grid may reveal why power companies try to keep the frequency as
stable as possible.

I'm definitely no expert here, but I'll bet it is definitely in the
power company's best interest.

Upteen million clocks around the world wouldn't be using the principle
if it was unreliable.


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2001\02\22@171757 by Don Hyde

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The US is hooked up into a single power grid so that power can be shared
from one region to another over long distances.  In order to do this easily,
it is necessary for all the generators not only to be producing the same
frequency, but the same phase as well.

AC motors and generators (which are pretty nearly the same thing) are a lot
like stepping motors we are familiar with.  For a given phase of the power,
their rotors want to be in a corresponding physical position.

If you tie two generators together that are not in phase, the one that's
ahead will supply current to the one that's behind, which will act as a
motor trying to catch up (which will also load down the one that's ahead,
slowing it down).  To do this, they will exchange current -- a lot of
current, because they will want to do this as nearly instantaneously as they
can.

So the load is getting heavy, and someone goes to switch on another
generator to handle the load, but it's out of phase.  Humongous relays clang
closed, and huge currents rush about as rotating machines as big as houses
jump and buck and make the ground shake, and the lights dim.

Actually what happens is circuit breakers take both generators off line
before something breaks, and now the grid really is overloaded...

Power companies pay a whole lot of attention to frequency and phase.  They
coordinate this, and keep the whole grid locked to very precise frequency
standards.  Sometimes when the load is heavy, they do get behind a few
cycles, but later on when the load lightens, they speed up.  If you observe
an electric wall clock carefully and compare it to something like WWV, you
may see it get a few seconds behind on a hot summer afternoon, but it will
be caught up by the next morning.

So the grid, at least in the US has great long-term stability, but only
pretty good short-term.

> {Original Message removed}

2001\02\22@233041 by Nikolai Golovchenko

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In Ukraine these clocks just don't work correctly. Currently we have
the mains frequency at about 49.3 Hz, and if you assume the frequency
is 50 Hz... :)

Nikolai

---- Original Message ----
From: Tony Nixon <.....Tony.NixonKILLspamspam@spam@ENG.MONASH.EDU.AU>
Sent: Thursday, February 22, 2001 23:49:33
 To: PICLISTspamKILLspamMITVMA.MIT.EDU
Subj: [OT]: Re: [PIC] Timer Tribulations

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2001\02\22@233538 by Tony Nixon

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Nikolai Golovchenko wrote:
>
> In Ukraine these clocks just don't work correctly. Currently we have
> the mains frequency at about 49.3 Hz, and if you assume the frequency
> is 50 Hz... :)
>
>  Nikolai


It'll give you more time to relax ;-)


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2001\02\22@233809 by Herbert Graf

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The thing to remember is it's not the actual frequency accuracy that counts
so much, it's the synching of phase that does. If they run the grid at
49.3Hz that's fine, as long as every generator is running at that frequency
with the same relative phase. TTYL

> {Original Message removed}

2001\02\23@033439 by Vasile Surducan

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On Fri, 23 Feb 2001, Tony Nixon wrote:

> Nikolai Golovchenko wrote:
> >
> > In Ukraine these clocks just don't work correctly. Currently we have
> > the mains frequency at about 49.3 Hz, and if you assume the frequency
> > is 50 Hz... :)
> >
> >  Nikolai
>
>
> It'll give you more time to relax ;-)
>
 I don't know why, but you ( americans ) look more relax than we are...
Even when you have painted the moon with  coca-cola sign, you found it
already painted in red... at 49,3 Hz

 Zdrasvuite Nicolai,
 Cheers Tony,

Vasile

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2001\02\23@052917 by Roman Black

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Hey! All this talk about clocks and 50Hz/60Hz mains
timing and getting crystal clocks accurate just
gave me a clever idea!

Using mains sync is probably the best for accuracy,
but has problems due to needing to provide a mains
supply and then insulate high voltages or use
a transformer etc. Just not practical for a
battery powered PIC device on the wall.

So how about this: Every time I use a high gain
input on some circuit and put the cro on it there
is always some 50Hz mains freq clearly visible
on the signal. Yes even on battery driven circuits.
Seems the average house has quite enough mains driven
devices and mains wires running through all the
walls that there is a very definite 50Hz/60Hz
RF signal everywhere in suburbia.

So... How about a simple two transistor high-gain
amp (or op amp) tuned for about 50Hz. This could
be fed into the PIC pin. Sure there would be some
ocassional false triggers but the PIC could be
smart enough to log input triggers in software
and "decide" which are the real ones based on the
general timer period which is always known.

If done correctly you could have a battery powered
PIC device anywhere in your home, mains sync'ed
and running with perfect time accuracy. And never
have to actually connect it TO the mains.

So this is the point where some smartie normally
says they already thought of it and have been
making them for years... ;o)
-Roman



Tony Nixon wrote:
>

> > > You will find that the clock will drift one way or the other depending
> > > on temperature, so using the mains as a frequency source is much more
> > > accurate.
> >
> >   You are certainly joking ! Or in your country mains frequency drift is
> > under 0.5% ...

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2001\02\23@060754 by Roman Black

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Nikolai Golovchenko wrote:
>
> In Ukraine these clocks just don't work correctly. Currently we have
> the mains frequency at about 49.3 Hz, and if you assume the frequency
> is 50 Hz... :)
>
>  Nikolai



Ha ha! So they are ripping you off 0.7Hz!!

You are getting less than what you pay for,
I wonder if that applies, seriously??? :o)
-Roman

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2001\02\23@062040 by Roman Black

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Vasile Surducan wrote:
{Quote hidden}

Ha ha! Friendly competition!! :o)

Hey, I just realised, the Coca Cola sign already
IS red!! Is that telling us something??? ;o)
-Roman

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2001\02\23@074924 by Nikolai Golovchenko
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Well, isn't Tony from Australia? :)

I guess people in California are supposed to be most relaxed ... for a
number of reasons... :)

Let the light be!

Nikolai

---- Original Message ----
From: Vasile Surducan <vasilespamspam_OUTL30.ITIM-CJ.RO>
Sent: Friday, February 23, 2001 10:17:34
 To: @spam@PICLISTKILLspamspamMITVMA.MIT.EDU
Subj: [OT]: Re: [PIC] Timer Tribulations

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2001\02\23@074929 by Nikolai Golovchenko

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They rip us anyway!

Usually houses don't have gas, heat or water counters. So everyone
pays an "average" rate relative to apartment size. I heard the tenants
of an apartment house installed the counters, and the actual payment
should have been something like 20% less. But no one lets them pay
less!!

Seriously, the problem with low frequency, as far as I know, deals
with overloaded power system. There are shortages of fuel, etc... And
also someone decided to shut down the Chernobyl nuclear station. :)

Nikolai

---- Original Message ----
From: Roman Black <KILLspamfastvidKILLspamspamEZY.NET.AU>
Sent: Friday, February 23, 2001 13:09:22
 To: RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU
Subj: [OT]: Re: [PIC] Timer Tribulations

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2001\02\23@080811 by Bob Ammerman

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Excellent idea Roman, just don't take the widget camping with you ;-)

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

{Original Message removed}

2001\02\25@165621 by Tony Nixon

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Vasile Surducan wrote:
>   I don't know why, but you ( americans ) look more relax than we are...
> Even when you have painted the moon with  coca-cola sign, you found it
> already painted in red... at 49,3 Hz
>
>   Zdrasvuite Nicolai,
>   Cheers Tony,
>
> Vasile

Ozzie mate :-)

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2001\02\25@165827 by Tony Nixon

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Roman Black wrote:
>
> Hey! All this talk about clocks and 50Hz/60Hz mains
> timing and getting crystal clocks accurate just
> gave me a clever idea!
>
> Using mains sync is probably the best for accuracy,

I thought about this ages ago, but I wonder how many 'ticks' get
corrupted when electric motors, welders, etc. etc. are started and
stopped.

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2001\02\25@193024 by Robert Rolf

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Tony Nixon wrote:
> Roman Black wrote:
> >
> > Hey! All this talk about clocks and 50Hz/60Hz mains
> > timing and getting crystal clocks accurate just
> > gave me a clever idea!
> >
> > Using mains sync is probably the best for accuracy,
>
> I thought about this ages ago, but I wonder how many 'ticks' get
> corrupted when electric motors, welders, etc. etc. are started and
> stopped.

Thats probably why those old clocks had little flywheels in them <G>.
They only tracked the average frequency, not the instantaneous one.
As if anyone would notice the cumulative 1000/60 error when their
alarm clock goes off.

R

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2001\02\25@221045 by Tony Nixon

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Robert Rolf wrote:
>
> Tony Nixon wrote:
> > Roman Black wrote:
> > >
> > > Hey! All this talk about clocks and 50Hz/60Hz mains
> > > timing and getting crystal clocks accurate just
> > > gave me a clever idea!
> > >
> > > Using mains sync is probably the best for accuracy,
> >
> > I thought about this ages ago, but I wonder how many 'ticks' get
> > corrupted when electric motors, welders, etc. etc. are started and
> > stopped.
>
> Thats probably why those old clocks had little flywheels in them <G>.
> They only tracked the average frequency, not the instantaneous one.
> As if anyone would notice the cumulative 1000/60 error when their
> alarm clock goes off.

I guess you could create a similar flywheel in software.

Keep track of the 50Hz signal and if a valid signal change occurs
outside a hysteresis point, ignore it.

Can also be used to provide a timebase for brief power outages.

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2001\02\25@222731 by Scott Dattalo

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On Mon, 26 Feb 2001, Tony Nixon wrote:

> Robert Rolf wrote:
> >
> > Thats probably why those old clocks had little flywheels in them <G>.
> > They only tracked the average frequency, not the instantaneous one.
> > As if anyone would notice the cumulative 1000/60 error when their
> > alarm clock goes off.
>
> I guess you could create a similar flywheel in software.

Yeah, but don't hit any breakpoints while you're simulating or your code will
crash!

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2001\02\25@234115 by Tony Nixon

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Scott Dattalo wrote:

> > I guess you could create a similar flywheel in software.
>
> Yeah, but don't hit any breakpoints while you're simulating or your code will
> crash!

Lose it's momentum don't you mean ;-)

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2001\02\26@025626 by Roman Black

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Tony Nixon wrote:
>
> Roman Black wrote:
> >
> > Hey! All this talk about clocks and 50Hz/60Hz mains
> > timing and getting crystal clocks accurate just
> > gave me a clever idea!
> >
> > Using mains sync is probably the best for accuracy,
>
> I thought about this ages ago, but I wonder how many 'ticks' get
> corrupted when electric motors, welders, etc. etc. are started and
> stopped.

That's why you use software correction to make
up for missed ticks, and only allow a small window
for tick timing. It should self-correct given that
it will receive 100 ticks/second.
-Roman

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