[time-nuts] GPSDO standard interface?

Bob Camp kb8tq at n1k.org
Thu Jun 26 10:44:35 UTC 2014


Hi

One gotcha with TISP <-> NEMA is that they use different units for things like position. Yes it’s just math to translate them. No it’s not trivial on a little tiny PIC. If the GPS in your GPSDO is a NEMA (or NEMA like) device, you either will have a mix of TISP and NEMA or a lot of translation ...

Bob

On Jun 26, 2014, at 5:38 AM, REEVES Paul <Paul.Reeves at uk.thalesgroup.com> wrote:

> Chris,
> NMEA is a good 'general purpose' interface for GPS units but I thought this thread was about the GPSDO interface. Not quite the same - TSIP/SCPI would make rather more sense here, especially with all those Thunderbolts about :-)
> Most GPS receivers still supply at least one serial interface even if a USB interface is included too. Consumer grade 'very small' navigation type GPS units may dispense with the serial ports but we are not too worried about those devices, surely? I don't see why a serial to USB converter would be needed - serial ports are still available on a reasonably large number of motherboards, especially if you are using mini-ITX or similar for embedded projects, and a hardware UART is a much more reliable interface. USB/serial adaptors 'still' give erratic results and scanning usb ports for new devices is also a bit of a lottery at times.
> A serial interface is also the easiest to convert to a more 'robust' physical media for electrically 'unpleasant' environments .... and DB9/25 connectors are a LOT more reliable than USB connectors too!
> 
> regards,
> 
> Paul    G8GJA
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On Behalf Of Chris Albertson
> Sent: 26 June 2014 08:13
> To: Bob Stewart; Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] GPSDO standard interface?
> 
> If you want a common interface for GPS receivers it's "NMEA" and it's
> relatively easy to implement.  I certain would NOT translate to TSIP as
> that is rather obscure.  NMEA is a very common standard and many GPSes can
> output NMEA.
> 
> Also you talked about "serial".  I hate to say it but "who in 2014 wants a
> serial device?  USB is the only reasonable interface to a computer.  If you
> used serial then you would just need to buy a serial to USB adapter so you
> may as well build that into  your controller.   In 2014 those old DB9 and
> DB25 connectors should be banned from all new designs.
> 
> Realistically the user interface in most home made gear is a few "#ifdef"
> in the code at the top of the file.  You change those and recompile and
> send the new software to the controller.  It's not bad having to re-compile
> in order to support a different GPS receiver.  You would not want to swap
> the brand of GPS in a user interface.  You do that with solder and wires
> and recompiling
> 
> 
> On Wed, Jun 25, 2014 at 8:14 PM, Bob Stewart <bob at evoria.net> wrote:
> 
>> After reading Chris's response, it dawned on me that I'm treading a
>> different path from what I've seen on the list.  It's not so much a GPSDO
>> as a general purpose GPSDO engine.  It uses a number of ideas from Bert's
>> board, like the dual-rail op-amp output, but it also has a TIC, so it will
>> have sawtooth correction.  I have included 2 TTY ports: one for the
>> receiver and one for the PC interface.  I'm going to use the DAC on the
>> dsPIC, but there will be an SPI port that can be used to drive an off-board
>> DAC, instead.  There's also the possibility of switching some stuff around
>> and having an I2C port, and the ICSP header could also hook up to an
>> additional thermistor or two, or perform other digital functions.
>> 
>> 
>> So, there will be some minor user fiddling, like with Bert's board, due to
>> the flexibility of the OCXO.  But, I'll be using the P and D from the PID
>> control system, so it shouldn't be difficult to setup.  There will be a
>> power LED, an output enable LED, and a bi-color LED to signify status, but
>> only the status would be necessary.  I'll do what I can to make it smart
>> enough to plug and play for most circumstances, but I only have the one
>> OCXO brand to test with at the moment.  I do have 3 receivers to test with
>> now: Adafruit, UT+, and LEA-6T.  Keep in mind that I don't expect this to
>> be a lucrative commercial business venture, so my budget is almost
>> nonexistent.
>> 
>> 
>> I'll look into both SCPI and TSIP, and therein lies the reason for my
>> original post.  Essentially, have they been patented, and if so, have those
>> patents expired?  Some companies guard their interfaces very rigorously to
>> forestall competitive disruption.  I don't want to suddenly get a cease and
>> desist letter or a notice of lawsuit over a hobbyist kit.  It's one thing
>> to provide open source software to monitor/control a successful product.
>> It's an entirely different thing to provide an alternative product with an
>> identical user interface.
>> 
>> I just ordered the first prototype boards today, but the software should
>> be just a rewrite of what I did for the TIC on Bert's board, with a lot of
>> extras thrown in.  Not that that doesn't mean a lot of work, of course.
>> 
>> 
>> Bob
>> 
>> 
>> 
>> ________________________________
>> From: Tom Van Baak <tvb at LeapSecond.com>
>> To: Discussion of precise time and frequency measurement <
>> time-nuts at febo.com>
>> Sent: Wednesday, June 25, 2014 9:02 PM
>> Subject: Re: [time-nuts] GPSDO standard interface?
>> 
>> 
>> Bob,
>> 
>> A couple of different ideas:
>> 
>> 1) No UI at all. The surplus GPSDO favorites over the years (like the HP
>> SmartClock's and Trimble Thunderbolt) work with no UI. Yes, there is a PC
>> program you can use to monitor and control it, or even debug it, but it is
>> completely optional. Many GPSDO work out of the box. Maybe, like HP, have
>> one green LED to say all-is-well.
>> 
>> 2) A very simple 9600 baud command set that you can use with any terminal
>> program. Adding LCD is fine too. But make sure everything on the LCD is
>> also available over RS232. Not everyone wants to visually monitor the LCD
>> of every piece of gear on their bench; let a PC log and archive all the
>> data, check for problems, make plots, etc.
>> 
>> 3) Mimic enough of HP's SCPI command set so that GPScon and other tools
>> like that can be used, transparently. I forget if your GPSDO includes a
>> receiver or not.
>> 
>> 4) Mimic enough of Trimble's TSIP so that LH and other tools like that can
>> be used, transparently.
>> 
>> Please write enough code so that the GPSDO, by default, can work "out of
>> the box". I'm evaluating a prototype GPSDO right now that requires all
>> sorts of user input just to get it started and to keep it going. That gets
>> old. My bias is: time spent creating clever adaptive algorithms to make a
>> human unnecessary is better than time spent creating an elaborate UI that
>> requires a user (and operation manual) and constant monitoring or adjusting.
>> 
>> /tvb
>> 
>> 
>> ----- Original Message -----
>> From: "Bob Stewart" <bob at evoria.net>
>> To: "Discussion of precise time and frequency measurement" <
>> time-nuts at febo.com>
>> Sent: Wednesday, June 25, 2014 5:10 PM
>> Subject: [time-nuts] GPSDO standard interface?
>> 
>> 
>> In an offline communication, I suddenly realized that I hadn't given any
>> thought to the user interface for my GPSDO. Is there an accepted standard
>> interface for GPSDOs, or is that a murky Microsoft-esque world of patents
>> and lawyers?
>> 
>> 
>> Bob - AE6RV
>> 
>> 
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>> 
> 
> 
> 
> --
> 
> Chris Albertson
> Redondo Beach, California
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.




More information about the Time-nuts_lists.febo.com mailing list