[time-nuts] is there a "best bet" advanced hobbyist buildable GPSDOdesign?
bruce.griffiths at xtra.co.nz
Wed Dec 12 15:50:42 EST 2007
Scott Burris wrote:
> Bruce Griffiths wrote:
>> Do you also want a circuit for a sawtooth corrector using one of the
>> Maxim/Dallas programmable delay lines?
> Yes! I now feel inspired to go spin a design after studying all of
> these messages in this
> thread. My only constraint is that the parts have to pass the "Digikey"
> test, i.e. I have to
> be able to order small quantities from Digikey, Mouser, or the like.
> It's nearly impossible
> for a hobbyist like me to get small quantities of more exotic parts.
> The big distributors have
> gotten better in the last decade about taking small orders, but still
> often have minimum qty/piece
> requirements that they won't waive. Even worse are orderable, but
> unobtainable parts -- Maxim
> seems to have a huge library of such "virtual" chips that have lead
> times of 1/2 year or more.
I usually checkout the availability of parts in small quantity from such
sources, although which suppliers to check depends on your location.
Locally RS Components and Farnell are very good (they are also good
sources in Europe). I have a Digikey printed catalog with prices in my
local currency($NZ) (I have ordered a few things from them when I cant
easily get them locally). Linear Technologies on line ordering facility
works well for some of their more exotic parts and evaluation kits.
As far as I know Dallas/Maxim appears to be the only source of suitable
affordable programmable delay chips for this particular application.
In principle one could use a tapped chain of gates in a CPLD, however
continuous calibration of the delay is required (a delay locked loop
controlling the gate propagation delay by adjusting its power supply
voltage to compensate for the effect of temperature variations is one
technique). However unless the Dallas chips become hard to obtain its
probably best to leave this as a backup option.
What processor are you intending to use to decipher the sawtooth
correction messages from the GPS timing receiver?
You could use an inexpensive microprocessor dedicated to this simple task.
Another microprocessor can be used to discipline the OCXO.
Depending on your experience, this can be easier than using a single
microprocessor to do everything.
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