[ntp:questions] Motorola Oncore GPS as Stratum 1 source

Thomas Laus lausts at acm.org
Thu Oct 18 13:09:42 UTC 2012


On 2012-10-17, Hahn, Ron <ron.hahn at fmr.com> wrote:
> Colleagues,
>
> I am putting together some Motorola Oncore UT+ boards to replace my
> Sure boards in my ntp servers.  I am using this
> http://www.tapr.org/gps_vpib.html board as the templat for the
> interface circuits.  The circuit calls for a BR2325 battery which
> I cannot find in the local parts store.  Is there a person on this
> list with experiences of this board design that can tell me what I
> can substitute for this part?  Or maybe it is not necessary?  I am
> not even sure if the battery is necessary but from my experiences
> the boards go from a cold start whenever power is interrupting.
> One of my servers is part of the ntp pool so I am needing the
> rapid recovery if the power is interrupted. My systems are on
> the UPS so maybe this battery is not required?  
>
Ron:

I am also using this same board and made a discovery a few years ago
that this backup battery discharges over a period of time, normally
less than a year and is not available when 'really' needing it.  There
is a battery charging current available on Pin 3 of your Oncore that
can be used to charge a 1.5F 5.5V Gold Capacitor.  I used the Digikey
part P11063-ND for mine.  It will mount in the same loacation as the
coin cell.  You will need to jumper out R2 (820K) and just connect the
high Farad capacitor between pins 1 & 3 on your Oncore.  Watch the
polarity!  The charging circuit in the Oncore is current limiting and
it will take about 12H for enough charge to hold the almanac between
powerups.  When the capacitor is fully charged, the almanac stays for
about a month.

You really can't do without a battery.  Your almanac information and
current date and time is stored in the Oncore RAM.  Your GPS location,
and other parameters get saved in Flash, but the Oncore will require
about 30-40 minutes to recover from a power outage before it can serve
up time again. 

Tom

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