[time-nuts] inexpensive, black box, GPS or NTP based TTL time capture?

Bob Bownes bownes at gmail.com
Wed Oct 18 18:02:38 UTC 2017

So, if I hear you right, you want a ttl input to trigger a timestamp,
accurate to ms or µs to a file, correct?


On Wed, Oct 18, 2017 at 1:33 PM, Rob Seaman <seaman at noao.edu> wrote:

> Attila Kinali wrote:
> > On Wed, 18 Oct 2017 08:47:58 -0600
> > Rob Seaman <seaman at noao.edu <https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts>> wrote:
> >
> > > I’m at the annual planetary sciences meeting (in Provo this year) and
> several
> > > groups have expressed interest in duplicating our setup (details of FO
> > > converters, Schmitt triggers, etc, omitted) in a “cheap black box” to
> quote
> > > one fellow. Lots of people contribute productively to NEO observations,
> > > including amateurs and small teams with little funding. Improving their
> > > timekeeping would help keep rocks from falling on you and your family.
> >
> > What is this black box supposed to do? Just provide a PPS? IRIG-B?
> > Or does it need to have time-stamping capabilities? If so, how many
> > channels?
> >
> > What are your time precision/accuracy requirements?
> >
> > What how cheap is "cheap"? What is the volume?
> Thanks for the quick reply. I should have included the subject line in the
> message:
>         "inexpensive, black box, GPS or NTP based TTL time capture”
> Telescope domes are filled with equipment, in particular the camera
> shutter, that can be instrumented to issue a pulse suitable for hardware
> time capture. We use Meinberg IRIG PCIe cards to trap these and read the
> timestamps using their library routines under Linux. “Black box” to the
> person I was talking to meant no IRIG in the dome, no Linux, and no PCIe
> slot, but rather a self-contained unit that syncs to GPS. When last he
> implemented such a feature at another telescope he didn’t even have time
> capture, but rather the device issued a trigger at a specified moment, so
> the timestamp and the shutter opening were inverted. He also seems to
> prefer the timestamps be issued on a serial connection, not via library.
> Unlike laboratory instrumentation, a telescope environment needs to be
> both very automated and very forgiving. Money may also be constrained.
> However, telescopes are also often very flexible and I am willing - no,
> eager - to consider completely different arrangements of equipment.
> So, reliable timestamping of a TTL input is the ulitmate goal. One channel
> would be sufficient, but multi-channel would not invalidate an option. PPS
> or IRIG-B (DCLS IEEE-1344) are not required, but might form an intermediate
> part of the solution. Reference could be GNSS or possibly NTP.
> Precision varies, but milliseconds down to microseconds. Accuracy should
> match the precision, meaning UTC accurate to same. Extra credit for
> multiple timescale support.
> Cheap is what I want to know. I see the previous thread on BB-black and
> could imagine a solution using the real time capabilities of that for a few
> hundred bucks, but these are not experimenters, per se. That’s why they
> want a black box. Volume is one to several, but could imagine a bulk order
> if savings were significant. Hundreds of dollars might be the price point.
> Thanks!
> Rob Seaman
> University of Arizona
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