[ntp:questions] almost decided which new PPS GPS to buy

Ron Frazier (NTP) timekeepingntplist at c3energy.com
Sun Mar 4 22:37:35 UTC 2012


Thanks for the info.  Comments inline.

On 3/4/2012 1:51 PM, David J Taylor wrote:
>> Hi all,
> []
>> From my reading, it appears that I need to add the following to the 
>> Sure Electronics package of parts:
>>
>> 1) DB-9 Male - DB-9 Female serial cable
>
> Correct.  I got mine from Amazon.  Search for "2m 9 Pin Serial / 
> RS-232 Extension Cable M-F".
>
>> 2) Motherboard header - DB-9 port adapter
>
> Correct, if you don't already have a serial port on your PC.  Check 
> that the motherboard has the COM port header, of course!
>
>> 3) Plastic box for mounting.  Misc hardware like screws, standoffs, etc.
>>
>> (David T. or others, I don't suppose you can suggest any specific 
>> part numbers for those hardware items from Radio Shack [do you have 
>> those in the UK], Mouser, or DigiKey.  Just thought I'd ask.)
>
> I used N90BQ from Maplin.
>  http://www.maplin.co.uk/eddystone-die-cast-aluminium-shallow-lid-thin-wall-43713 
>
>
> and filed out the openings for the connectors.

Interesting that you used a metal box.  I guess it doesn't matter since 
the antenna is external.  I think a clear lid might be cool to see the 
lights.

>
>> My plan of attack is as follows, although the sequence may vary:
>>
>> A) Get the unit working "at all", using USB NMEA data only.  I would 
>> hope to see performance equal to my BU-353.
>
> I only use USB for power.  Not data.
>
>> B) Get the unit working with NMEA data from the RS-232 port, going 
>> through a Trendnet TU-S9 USB - Serial converter, based on the 
>> Prolific chipset.  Performance should, again, be similar to the 
>> BU-353 (which also uses the Prolific chipset internally).
>
> Why bother?
>

I have three computers, all of which dual boot between some version of 
Windows and Ubuntu 11.04.  Two of those are laptops.  I also have an old 
Pentium 4 laptop which only runs Ubuntu.  (It makes a nice heater.  It's 
nickname in the industry is global thermonuclear reactor.)  I try to 
keep all of these 6 main configurations functionally equivalent.  I'd 
like to be able to plug a GPS into any one and have it work, with any 
OS.  Two of the three main PC's are laptops, with no real serial port.  
I started with the BU-353 on one particular laptop.  That unit has a 
built in Prolific serial - USB circuit.  I'm curious to see how the 
performance is using an external serial - USB chipset (which just 
happens to use the same chipset).  For the two laptops, USB is the only 
way into the machine.  Also, I may want to use the laptop for navigation 
some day.

>> C) Get the unit working with NMEA data from the RS-232 port, going to 
>> a real serial port.  I have to tinker with the motherboard on another 
>> computer to do that.
>
> Find an old computer with a serial port, and run the software Sure 
> provide.
>
>> D) Get the unit working with NMEA + PPS, with data from the RS-232 
>> port, going through the TU-S9, which claims to pass all the 
>> handshaking signals.  I'll have to do the mods that David recommends 
>> on the board for this.  Hopefully, the same procedure will still work 
>> on the recent boards.  This is where I'm hoping to get + / - 1 ms 
>> performance.
>
> Why bother?
>

Mainly curiosity.  I'm getting + / - 6 ms from a USB only device now.  I 
want to see what the max performance I can get with USB with handshaking 
is possible.  I think I can break the + / - 1 ms barrier.  Why do you 
climb Mount Everest - because it's there!  PS - I would never climb 
Mount Everest - I hate high places with steep cliffs and without walls - 
and I hate the cold.

>> E) Get the unit working with NMEA + PPS, with data from the RS-232 
>> port, going to a real serial port on the other computer.
>>
>> This should be an interesting adventure, hopefully ending with a time 
>> server running at 100 us accuracy or better.
>>
>> Sincerely,
>>
>> Ron
>
> You are confusing me with how many computers you have!  Designate one 
> as your stratum-1 server, and get it right, with the serial I/O, 
> adding the header should you need it.
>

See comment under B above.  Also, as a curious engineer, I like to 
compare performance on different environments and systems.

> As you already have something which works, I would take a much more 
> aggressive approach.
>
> - get serial I/O somehow and check the unit works, applying power via 
> the USB lead.
>
> - carefully, add the PPS/DCD modification (two wires to solder) which 
> translates the TTL-level from the board to the RS-232 level required 
> by the PC.
>
> - use my Serial LEDs program to verify the PPS signal.
>
> - configure NTP around the new unit.
>
> Have fun!
>
> Cheers,
> David

Thanks for the help.  I'm not the best with mechanical things, I'm 
better at electronic or software things.  However, I can work my way 
around a screwdriver, wrench, Dremel tool, and soldering iron if I have 
to.  If I can even find those tools, but that's another story.  I'm sure 
parts of this will be fun, and I'm sure the project will be 
interesting.  I'll try to report back on my findings.

Sincerely,

Ron


-- 

(PS - If you email me and don't get a quick response, don't be concerned.
I get about 300 emails per day from alternate energy mailing lists and
such.  I don't always see new messages very quickly.  If you need a
reply and have not heard from me in 1 - 2 weeks, send your message again.)

Ron Frazier
timekeepingdude AT c3energy.com



More information about the questions mailing list