[time-nuts] Next step up from basic GPS/PPS timekeeping

Jim Harman j99harman at gmail.com
Thu Feb 25 16:07:20 EST 2016


On Thu, Feb 25, 2016 at 1:08 PM, Neil Green <ncguk at hotmail.co.uk> wrote:

> I’ve decided to build this:
>
> http://www.hackersbench.com/Projects/1Hz/
>
> which has an easy to follow diagram. Parts have cost less than £5. I’m not
> expecting great things from it by any means, but it’s something I can get
> my head around and should improve my understanding (a little).
>

Good start!

Once you have built it and observed how sensitive it is to temperature
variations, you might want to take a look at this:

https://www.adafruit.com/products/3013

This breakout is based on the DS3231 chip, which is a temperature
compensated 32 KHz real time clock with a built in crystal and optional
battery backup.  It also has a 1 pps output.

It is reasonably stable and accurate out of the box, but if you want to
adjust it you can send it commands from a microprocessor that tweak its
frequency up and down in increments of about 0.1 ppm (about 3 seconds per
year). It does this by switching in and out tiny on-chip capacitors.


-- 

--Jim Harman


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