[time-nuts] Local Solar Time Clock
Tom Van Baak
tvb at LeapSecond.com
Sun Jan 19 14:21:07 EST 2014
> Yeah.. that *is* the challenge.
> Use two outputs and make a sort of "H bridge"
1) equation of time:
See www.leapsecond.com/tools/eot1.c, source code that generates the equation of time and its derivative. Sample output attached. You can see the time varies from about -14 minutes to +16 minutes. The clock rate varies from -28 seconds to +22 seconds per day, which is about -324 ppm to +262 ppm. This is easy to do with "leap cycles" on a microcontroller. See my sidereal PIC code for an example: http://leapsecond.com/pic/src/pd28.asm
2) quartz clock stepper motor:
For waveforms of a typical quartz clock see PDF page 13-17 of http://leapsecond.com/ten/clock-powers-of-ten-tvb.pdf
See http://leapsecond.com/tools/comtick.c for an example of a PC program that drives a quartz clock stepper motor from a serial port.
When driving a quartz clock stepper motor from a microcontroller, the trick I use is to configure two pins as *input* (tristate), and set output latches to 0 and 1. Then once a second all you do is change the mode to *output* for 50 ms. During the 950 ms idle time, XOR the two output latches with 11.
That way you get the identical waveform as seen in the oscilloscope trace above. Pick current limiting resistors such that the clock ticks confidently but not violently.
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