[time-nuts] Mains Frequency -again

[Andy Talbot]

Well, I do everything in PICs with a assembler, but you have a point.  A
flash memory chip is one route.  An FTDI Vinculum and USB memory stick,
another.
Andy
www.g4jnt.com



On Wed, 24 Feb 2021 at 14:05, Dan Kemppainen <dan at irtelemetrics.com> wrote:

> Andy,
>
> Perhaps one of the little openlog units from sparkfun, or one of the
> clones would work for logging?
>
> https://www.sparkfun.com/products/13712
>
> Honestly, I have two and a pair of 32Gb Cards, but have not tried them
> yet. Seems like a good solution for a project like this. I don't know
> how they buffer writes to the microSD, or what the write life on an
> SDcard would be like.
>
> Dan
>
>
> On 2/24/2021 7:35 AM, time-nuts-request at lists.febo.com wrote:
> >
> > My monitor uses a 16F628A PIC device clocked from a 10MHz TCXO.   50Hz
> > mains is fed to the  capture/compare module which is set to measure the
> > number of periods of the prescaled clock in every fourth cycle of the
> > mains.  A simple integer division and the answer is the mains frequency
> in
> > milliHz units..  I only measure to about 0.002Hz resolution as the
> > variation is so wide (~~ 0.2Hz RMS) this is quite enough .
> > Completely separately, a four bit counter is incremented by this divided
> > mains signal every 80ms, and also decremented every 80ms by the divided
> > down clock.   Software is written so that increment and decrement cannot
> > clash.
> >
> > The result is a 32 bit twos-complement count, to 80ms resolution, of
> mains
> > timing difference from that of the TCXO.   A bit of arithmetic and the
> > answer can be shows as a timing discrepancy in seconds on the display.
> >
> > It would be a matter of just a few minutes of extra code writing to add a
> > serial output to transfer data to a logger .   Which I may yet do, but
> that
> > would require getting an old laptop out of storage and leaving it on 24/7
> > to do the logging - don't keep my main PCs on continuously.
> >
> > Not sure this list passes-through attachments;  if not the oicture is
> here
> > http://www.g4jnt.com/DropF/img2783.JPG
> >
> > Andy
> > www.g4jnt.com
>
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