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

David J Taylor david-taylor at blueyonder.co.uk.invalid
Sun Mar 4 18:51:19 UTC 2012


> 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.

- use my Serial LEDs program to verify the PPS signal.

- configure NTP around the new unit.

Have fun!

Cheers,
David 



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