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

unruh unruh at invalid.ca
Sun Mar 4 20:22:39 UTC 2012


On 2012-03-04, David J Taylor <david-taylor at blueyonder.co.uk.invalid> 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.
>
>> 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?
>
>> 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?
>
>> 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.
>
> 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.

Again, almost no serial ports need this. They work fine off TTL level.
While it is true that the standards say -5 to 5 V almost all accept
0-5V. Now you can try it, and if it does not work, then go for the two
wire solution. But if you are at all klutzy with a soldering iron, try
the first first. 



>
> - use my Serial LEDs program to verify the PPS signal.
>
> - configure NTP around the new unit.
>
> Have fun!
>
> Cheers,
> David 
>



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