[time-nuts] Local Solar Time Clock

Jim Lux jimlux at earthlink.net
Sun Jan 19 14:28:53 EST 2014


On 1/19/14 11:21 AM, Tom Van Baak wrote:
>> Yeah.. that *is* the challenge.
>>   Use two outputs and make a sort of "H bridge"
>
> Jim,
>
> No problem.
>
> 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
>

> 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.
>
Exactly what I was going to do..


> 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.
>

So it's one pulse per second, with the polarity alternating on each pulse...

Easy enough..





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