Notes

Program Description : Overview : Files

If you wish to contact the Author

email sidereal at cashin dot net [use symbols and no spaces].

Display of UTC and LMST when GPS signal is lost

If the GPS signal is corrupted or lost, display of LMST will continue for several seconds using interpolated data (described elsewhere). This is indicated visually by lighting the decimal point on the first digit of the display. Normally this should light only once every 6 minutes when there are two sidereal seconds in one UTC second. If it lights more frequently then there is a problem which should be investigated. If the display is set to UTC, the display is only updated for valid GPS messages, so it will 'freeze' if the signal is lost.

Thoughts about enhancements

This project was started with the aim of producing a simple sidereal clock, and that has been achieved. This may be of great interest to many people or of little interest to anybody. If there is no interest, there seems no point in making changes to the design, it can remain an indulgence on the author's part. However, if there is interest, it may be worth taking things further. The PIC processor has not been used to its full extent, there is unused memory, some unused I/O pins, and the USART TX is not used. Some ideas for enhancement:

• Add the ability to advance/retard the clock by a small amount to compensate for the UTC/UT1 offset and the LMST/LAST offset. This would require some sort of menu structure and a  few pushbuttons. What would be the range and granularity? e.g. +– 1 second in 0.1 second steps.
• Add the ability to vary the brightness (see the documentation for the MAX 7219 chip). At the moment the brightness is set low.
• Add a stopwatch facility where a signal is input to one of the pins, and a timestamp is output on the serial port. This could have quite a high resolution, e.g. to 1/100 second. The capture could be on both rising and falling signal connected e.g. to a photometer to measure a transit (I am making this up as I have no clue if it is useful).
• Add a second display to output both UTC and LMST. It takes about a millisecond to update the displays, so one of them will be delayed when both seconds start concurrently.

I considered displaying local civil time, but rejected the idea. It doesn't require much mental gymnastics to convert UTC to local time, especially if it just to set another clock.

Any thoughts?