[time-nuts] accurate portable time source

Brooke Clarke brooke at pacific.net
Fri Dec 28 18:19:49 EST 2007


Hi Ronald:

Here are a some of ideas for the heart beat for a LCD based clock like the ones 
I've been developing.

Best) A Vectron EX-380 series Vacuum OCXO only draws 0.35 Watts and if the 5 
volt version that's only 70 ma.  So a single AA would have enough energy, three 
AAA Ni-MH would be great.  That was the good news.  The bad news is that they 
are made of unobtanium (i.e. very expensive or need to be bought in large lots).

Good) An alternative is the DS3231.  This is an advanced version of the DS32khz 
TCXO and is adjustable to 0.1 ppm using the digital serial interface. 
Provision for a coin cell back up battery.

unknown) One of the DS3231 parts, in a thermal enclosure that has a time 
constant in excess of 24 hours.  I think it's about the size you request.  A 
temperature sensor changes the divisor based on calibration data.  Sort of a 
doubly compensated device TTCXO or T2XO.  I like this one for a practical product.

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.precisionclock.com
http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Cam


Ronald Held wrote:
> This request is different than the last one.
> The most accurate TCXO watch is about 1 seconds/year, with regular
> wear and lots of adjustment. For at least 1 order of magnitude in
> accuracy, what can be made/bought given these initial requirements: it
> has to run of its own power supply for ~18 hours a day, and recharge
> fully at night. the device must be intrinsically accurate without be
> disciplined by an external signal, although that could be done at
> night. The size and wei8ght need to be pocketable such a a large cell
> phone.I am open to all suggestions and more/altered requirements.
>                                         Ronald.
> 
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