[ntp:questions] almost decided which new PPS GPS to buy
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.
> 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
>> 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.
> 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!
More information about the questions