[time-nuts] Local Solar Time Clock

[Chuck Harris]

The usual quartz clock that runs off of a AA cell is a little
trickier to drive than you might think.  You need to feed
its stepper motor coil with an alternating +1.5V and -1.5V pulse.
The pulse follows the rising or trailing edge of a 1/2 Hz square
wave.  I have driven them using a series capacitor and resistor
to ground...arranged as a differentiator, but I don't recall the
part values anymore.

You arduino could certainly be made to generate such a pulse using
a couple of resistors and a couple of digital outputs in a simple
DAC sort of circuit.

-Chuck Harris

Jim Lux wrote:
> On 1/19/14 2:00 AM, P Nielsen wrote:
>> To Jim Lux. After you get it working, would you consider putting the details
>> online, or selling as a kit?
>>
>
> Half coded.
>
> I'll publish all the details..
> It's pretty easy.. a Arduino, a clock, a wall wart to power it.  I haven't tried it
> yet (no clock to test with until the stores open), but I'm assuming that it's just a
> wire from the digital output port to the clock.  Might need a resistor in series.
>
>
> The other burning question is "how accurate" does it have to be. The scheme I have
> now basically has a table of "rate" vs day of year (which I still need to calculate).
>
> Right now, the EOT is changing almost 30 seconds/day, which implies that the clock
> could be some seconds off during part of the day (although "true" at noon).
>
> Given the tens of ppm accuracy of the crystal = some seconds/day it seems that I want
> a bit better algorithm.
> Rather than drive from a table, maybe actually calculating it. the Arduino is no ball
> of fire for floating point computation, but still, it doesn't have that much to do.
> It could be that I can just calculate the rate every second.
>
> But then I have to differentiate the equation of time... and I haven't had enough
> coffee yet to differentiate the chain of sinusoids analytically.
>
>>
>>
>> P Nielsen