[time-nuts] GPSDO standard interface?

Bob Stewart bob at evoria.net
Wed Jun 25 23:14:05 EDT 2014

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.


 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?


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.


----- 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

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