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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. 76 Silicon Chip 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 siliconchip.com.au 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. siliconchip.com.au Australia’s electronics magazine December 2021  77