sidereal clock for sale

On Fri, 14 Apr 2017 08:40:36 +0100, Martin Brown
wrote:

The way I did it was make a normal clock using a LCD display and 16F877
and provide a switch to allow solar or sidereal timekeeping with an
ability to tweak the second and digitally correct to 1ppm daily.

I built a sidereal clock back in the 1970s. I used discrete TTL logic
and a standard crystal (I don't recall the frequency- probably 10 or
20 MHz). It's easy enough to divide that down to get sidereal seconds
with quite high accuracy.

You only need an unusual crystal frequency if you're trying to convert
an existing clock into a sidereal clock.

If I were building a standalone sidereal clock today, I'd probably use
a small computer like an Arduino or Raspberry Pi and implement it in
software. This approach also makes it easy to keep the time synched
across a wireless network.

On 4/14/17 1:03 AM, Mike Collins wrote:
If an EMP destroys electronics I will be more worried about the lack of
food, water electricity and prescription medicine than sidereal time
clocks/.
Guns. Ya gotta have many many guns.

In sci.astro.amateur message b33eb50d-f4f9-44d5-aced-35c4500a6da2@googl
egroups.com, Thu, 13 Apr 2017 16:52:26, posted:


Convert An Existing Clock By Replacing the 32768 crystal with a 32858 crystal then calibrate it against WWV 1000 HZ tone using a variable
condenser of the right value. Sidereal time is simply one more day within the same civil year period. so like 32768 * 366.25/365.25 should be
the new frequency.

Use a readily-available 32768 Hz crystal clock and adjust it to run
accurately by normal time. One side of the crystal will be actively
driven at 32768. Tap it off, buffered, and use it as reference for a
phase-locked loop with a ratio of, say, one of these
365/366 1461/1465 12053/12086 146097/146497
which generates the right frequency for driving a sidereal clock. Use a
similar clock, if you like, and just remove the crystal and drive the
receiving side with your new frequency. If the result is wrong by about
8 minutes per day, use the reciprocal ratio.

https://en.wikipedia.org/wiki/Phase-locked_loop

Use something like a http://www.ti.com/product/CD4046B but possibly
faster.

http://www.ti.com/lit/ds/symlink/sn74lv4046a.pdf

Google for cmos pll ic

RS Components may still do good data/application sheets.


--
(c) John Stockton, Surrey, UK. Turnpike v6.05 MIME.
Merlyn Web Site - FAQish topics, acronyms, & links.

On Saturday, April 15, 2017 at 4:43:40 PM UTC-6, Dr J R Stockton wrote:
Tap it off, buffered, and use it as reference for a
phase-locked loop with a ratio of, say, one of these
365/366 1461/1465 12053/12086 146097/146497
which generates the right frequency for driving a sidereal clock.

That's one way.

But I'll admit that the method used by sidereal clock apps is probably simpler
even for an electronic circuit:

Determine the time of day. Determine the day of the year.

Add the day of the year as a fraction of the year to the time of day as a
fraction of a day - and get the sidereal time that way. As a bonus, one gets the
conventional time and date, so that the clock can be (accurately) *set* even if
you don't know what the current sidereal time _is_.

John Savard

What to make of people who try to conjure up two types of 'days' by trying to split apart the day/night cycle which constitutes a weekday ?. There are two day/night cycles due to separate rotations and where they combine we get the seasons so it comes down to basic familiarity with the polar day/night cycle where the Sun appears and disappears once each years from either poles and depending on where the Earth is in its orbit.

The fictional idea of a sidereal day apart from a solar day is a property of trying to bypass the central Sun as a reference for daily rotation and appealing to a rotating celestial sphere out to the point of Polaris and its Southern equivalent. Linking daily rotation directly to that rotating celestial sphere in order to justify RA/Dec is silly in the extreme
but who would know it ?.

The appeal of separate rotations and especially the rotation that represents the Earth's singular annual rotation due to orbital motion would draw in those who can distinguish between lunar orbital motion where one side of the moon constantly faces the Earth whereas the Earth does not demonstrate the same orbital behavior as it runs its circuit around the Sun.

If direct imaging of the planet's dual rotations doesn't make a difference then nothing will yet not everyone can be prone to celestial sphere reasoning -

https://www.youtube.com/watch?v=CFrP6QfbC2g

Draw a breath and allow the imaging of the motions tell their story.

On Sunday, April 16, 2017 at 3:43:16 AM UTC-6, Gerald Kelleher wrote:

The fictional idea of a sidereal day apart from a solar day is a property of
trying to bypass the central Sun as a reference for daily rotation and appealing
to a rotating celestial sphere out to the point of Polaris and its Southern
equivalent. Linking daily rotation directly to that rotating celestial sphere in
order to justify RA/Dec is silly in the extreme

but who would know it ?.

The Earth orbits the Sun, as Kepler discovered, in an *ellipse*, not a perfect
circle.

So while the Earth revolves on its axis at a nearly regular pace - one that was
more accurate than man-made clocks, before atomic clocks were invented - the
shape of the Earth's orbit means that the sundial is affected by the Equation of
Time.

Therefore, when astronomical observatories observed the heavens for purposes of
timekeeping, they did so by making transit circle observations of the stars.

And so referencing the Earth's rotation to the distant stars, rather than to the
Sun, does not seem at all "silly" to us here, but is instead the most natural
and obvious way to study the Earth's rotation in isolation, by itself, rather
than compounded with the Earth's orbital motion around the Sun.

I know you think differently about this than I, and others, do. But it's not
enough just to _say_ that something is silly. If you expect to convince anyone,
you will need to say _why_ it is silly.

John Savard

In an era when nuclear weapons are back on the agenda I wouldn't have the time to deal with the us/we of this forum although it is the only place I know to further the insights.The intrusions are more or less meaningless vandalism or graffiti by those who live in a bubble yet imaging is still pouring in even when interpretation doesn't keep pace.

VR technology looks like it would further many of the insights that were stitched together in this forum using graphics that were not originally dedicated to the components of a narrative. All it needs are people of courage,endeavor and stature instead of the dull and compliant that plague threads that are never meant for them.

The development of timekeeping from the original motion of a star from the left to the right of the Sun and its first annual appearance at dawn (right of the Sun) is a benchmark for many,many topics of discussion and development. It doesn't invite the mindless but it does require wider circulation.

On Sunday, 16 April 2017 22:44:48 UTC+2, Gerald Kelleher wrote:
In an era when nuclear weapons are back on the agenda I wouldn't have the time to deal with the us/we of this forum although it is the only place I know to further the insights.The intrusions are more or less meaningless vandalism or graffiti by those who live in a bubble yet imaging is still pouring in even when interpretation doesn't keep pace.

Is there a strong market for infant science fiction?

On Thursday, April 13, 2017 at 6:29:33 PM UTC-6, Quadibloc wrote:
On Thursday, April 13, 2017 at 6:23:58 PM UTC-6, Quadibloc wrote:
On Thursday, April 13, 2017 at 5:52:28 PM UTC-6, wrote:

Convert An Existing Clock By Replacing the 32768 crystal with a 32858 crystal

Um, isn't the problem that they don't _make_ 32858 crystals that you can just
easily run out and buy?

I found this thread:

https://forum.cosmoquest.org/archive...p/t-54749.html

Somebody ordered 500 custom quartz crystals at 32.8577 kHz, which is more
accurately the needed frequency. Maybe he still has some.

On a related topic, on my web page at

http://www.quadibloc.com/science/cal0501.htm

I recently made an addition, noting that a quartz crystal with a frequency of
4.95827 MHz would not only oscillate 495,827 times in one-tenth of an SI second,
but would also oscillate 509,458 times in one-tenth of a Martian second derived
by dividing the length of 88775.260726 second Martian day by 86,400. At least it
would be as accurate as the available precision for the length of the Martian
day is; 88775.2607260193575818... seconds per day.

Continued fractions are your friend.

John Savard

It seems that I used an incorrect figure for the length of the Martian solar
day. Using a correct figure instead, I now only need a 437.23 kHz quartz
crystal.

I haven't updated my web page yet with the correction, but I will soon.

John Savard