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
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