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CIRCUIT NOTEBOOK
Interesting circuit ideas which we have checked but not built and tested. Contributions will be
paid for at standard rates. All submissions should include full name, address & phone number.
Orrery (planetarium) using a Micromite LCD BackPack
An orrery (or planetarium) is a
model of the solar system showing
the position and motion of the planets. The oldest known orrery (called
the Antikythera mechanism) was discovered in a shipwreck in 1901 and
is thought to be over 2000 years old.
The first modern orrery was designed
in 1704, with the Sun at the centre of
the universe. This was presented to
Charles Boyle, the 4th Earl of Orrery
in 1704, and the term “orrery” was
coined. You can find further information about the history and development of orreries at https://w.wiki/3qv6
Traditionally, orreries were mechanical, but this one is electronic, showing
the position and motion of the planets on the Micromite’s colour touch
screen.
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It operates in two modes. The first is
similar to a mechanical orrery in that
the position of the planets is advanced
by one day every second. This shows
the motion of the planets relative to
each other, all revolving around the
Sun with the Moon revolving around
the Earth. Let’s call this demonstration mode.
Real-time mode shows a display for
any date and time from January 1st
1900 to any date in the future. Typically, the date and time will be set to
the current date and time, but can be
set to any date, for example, to find the
position of the planets on the day you
were born. The display then continues
to be updated in real-time.
There is also the option to display
the phases of the Moon, the position of
Australia’s electronics magazine
the Sun relative to the tilt of the Earth
and the rise and fall of the local tide.
The Sun is represented by a small
yellow circle in the centre of the display. Around the Sun are eight concentric circles representing the orbits
of the eight planets, and the position
of each planet is represented by either
a letter or an astronomical symbol. A
ring around the Earth represents the
orbit of the Moon, and a dot the position of the Moon.
Optionally, you can change the circles representing the orbits of the planets to ellipses. This makes better use
of the width of the screen.
The option to show or hide the
phases of the Moon is in the top lefthand corner, the position of the Sun
relative to the tilt of the Earth in the
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top right-hand corner, and the height
of the local tide in the bottom righthand corner. It can also show the time
in addition to the date in the bottom
left-hand corner. Note that the tide
and time are only displayed in realtime mode.
The display is updated once per
second in demonstration mode. The
display is updated each minute in
real-time mode if the time and/or
tide are displayed; otherwise, it is
every hour. Mercury moves approximately 4.1° every 24 hours, Venus
by 1.6° and the Moon by 13.4°. The
tide graphic increases or decreases in
height roughly every 9 minutes.
You would be lucky to see the outer
planets move – Neptune moves 1°
every 167 days! All positions are relative to the Earth’s northern hemisphere winter solstice. Between
screen updates, the Micromite clock
speed is reduced to 20MHz to save
power. Unfortunately, the touchscreen
appears to become inoperative below
20MHz.
Circuit description
The circuit of the Orrery is basically
identical to the Touchscreen Super
Clock from July 2016 (siliconchip.
com.au/Article/10004). That design
was essentially a BackPack with a
real-time clock module attached, and
this one uses the same hardware. The
only difference is that the Super Clock
could optionally get its time from a
GPS module, while the Orrery has no
such option.
The Micromite will use its built-in
clock without the real-time module,
but this can drift by a few seconds an
hour. Also, without the real-time clock
module, it will be necessary to set the
date and time each time the Orrery is
powered up.
Of course, the software is different,
and the BASIC source code is available
for download from siliconchip.com.
au/Shop/6/6051 When uploading the
BASIC code, make sure your Micromite LCD BackPack’s touchscreen has
been set up and touch calibrated as per
the BackPack articles.
Using it
When the Micromite is powered
up, it will immediately display the
orrery. If the DS3231 module has been
installed and previously initialised
with the correct date and time, this
will be shown in the bottom left-hand
corner of the screen. Otherwise, the
date and time will be set to the Micromite default of midnight on January
1st, 2000.
Touching the LCD panel will display
the setup screen with several options.
“Set date” will display three additional screens with a numeric keypad
to allow the correct date, time and then
time zone to be entered.
An incorrect entry can be corrected
with the “Delete” key and the date or
time saved with the “Save” key. If fitted, the DS3231 will be updated automatically.
The “Show / Hide moon”, “Show /
Hide time” and “Show / Hide earth”
buttons switch on or off the displays
in the corners of the screen. “Circle
/ Oval” switches between a circular
or elliptical display, while “Text /
Symbols” switches between alphabetic and astronomical symbols for
the planets. Real-time or demonstration mode is selected with the “Real
time / Fast mode” button.
The “LCD xx%” button sets the
brightness of the display, but this will
only have any effect if you have version 2 or later of the Micromite BackPack and have installed the optional
components for software control of the
screen brightness. Otherwise, you can
set the screen brightness via the trimpot on the Micromite PCB.
The set tide button shows an additional screen that allows the time of the
local high tide to be set and gives the
option to show or hide the tide display.
Note that over the long term, high
tides occur every 12 hours and 25
minutes, but individual high and low
tides can vary considerably, sometimes by up to an hour. As a result,
the tide display should only be used
as a rough guide.
Local tide tables for your area
should be readily available on the
internet, and it is probably best to look
at the pattern of high tides for your area
and choose one that falls close to the
average of 12 hours 25 minutes.
The tide display is based on the
local time that has been entered and
is unaffected by the time zone setting,
which only affects the position of the
planets and Moon.
The time of the local high tide
will need to be adjusted if your area
switches between winter and summer
time/daylight savings time.
Kenneth Horton,
Woolston, UK. ($120)
The Orrery screen can have the planet displayed by a letter or an astronomical symbol; the ring around the earth (‘E’)
defines the orbit and location of the Moon. The tide display at lower right is based on the entered local time and is
separate from the time zone setting which is used for the positions of planets and the Moon.
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