[time-nuts] Truetime dc 468 goes sat rcvr simulator basics working

Justin Pinnix justin at fuzzythinking.com
Mon Dec 6 20:44:42 UTC 2010


Paul,

That is very much appreciated.  I have one of these boxes.  I didn't realize
that the signal was no longer being broadcast, so at this point I'm all for
whatever hacks will make it useful.

Thanks,
-JP

On Fri, Dec 3, 2010 at 5:55 PM, paul swed <paulswedb at gmail.com> wrote:

> Well I think this puts me in the dangerous zone of time nuttery.
>
> I had posted to the group about a month ago about a Austron 2201 gps rcvr
> and any documents anyone might have. Russell responded and sent me some
> great documents on the Austron.
>
> In a phone conversation with Russell we started talking about the old
> Truetime dc 468s. Kind of got me thinking. I have been able to design a
> small single chip goes timecode simulator to drive these older clocks.
>
> The dc 468 was always quite attractive with their panelplex 7 segment
> displays. Have re-purposed the boxes for several other projects on occasion
> using the supply nd the displays.
>
> I find the dc 468s at flea markets still for $5 in the northeast US.
> Generally no converter assembly though it doesn't matter since the GOES
> timecode signals been gone since 2005.
>
> At the moment the software fits in a small parrallax SXB micro. Its written
> in basic language and compiled. Runs very fast with a 20 Mhz clock.
>
> At this stage the unit puts out a manchester encoded timecode signal and is
> injected at the very first data stage on the decoder. You have to do this
> to
> get the PLLs to lock so things decode correctly. I have not attached a GPS
> time signal to it yet and associated time decoding to automatically sync
> the
> clock. That will be the next item. But I suspect this will be a bit ugly.
> Like sync once per day type of behavior.
>
> Another interesting thing I discovered in this project. That the GOES 100
> Hz
> timecode actually transports a very stable frequency reference. So you need
> a pretty good 100 hz source. What this means is the clock will only drift
> as
> much as that source drifts. Thats why I think a single sync 1 time per day
> is most likely just fine. Additionally the internal 10 MC clock locks to
> the
> 100 HZ and is pretty stable. (Ok now I am in trouble. What on earth does
> that statement mean in this group?)
>
> As with the Loran simulator I will share the information with the group as
> it shapes up.
> For now I need to make sure the basic software actually is correctly
> keeping
> time.
>
> Regards
> Paul
> WB8TSL
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