Tech question: need a low cost NTP server

djmcmath · 10-23-2013, 05:34 PM

I'm building a DIY datalogger for the track. It's based around my elderly MacBook, and uses USB GPS and 3-axis inertial sensing to, basically, do Kalmann filtering to get a 100hz position.

The trick is time. The inertial sensor has it's own time reference, and it's "close enough" over the course of a half hour track session to be usable. The GPS, unfortunately, provides data on a "when I feel like it" basis. So the time that I'm getting from the GPS is within a second (or two), which is nearly useless.

If I synchronize with GPS time via NTP over my home network, then take it out for a run, it's shockingly accurate. The trick is that the track I run at doesn't have free wireless. So it's not standalone, and doggonit, it should be.

So I've found a number of really great NTP servers -- rack-mounted gigs that constantly get a GPS or CDMA signal, then distribute time to the network. But they're WAY expensive. I don't need anything like that. I really just need a high precision oscillator, e.g. a device that can connect to the network, get the time, then just keep track of it and distribute via NTP for a couple of days without a network signal.

Does a device like that exist?

Thanks,
Dan

PS -- for those who say "Just spend $600 and get a basic datalogger," I say "That's no fun. I'm doing this as a hobby."

Scott R · Scott R's Garage

Any tiny linux server can be an NTP server.

pitargue · pitargue's Garage

Doing a quick web search shows how to get Mac OSX be a NTP server. Would that work for you?

HardDrive · 10-23-2013, 07:08 PM

Not sure if this helps:

Building a Raspberry-Pi Stratum-1 NTP Server

US source for Raspberry boards:

Raspberry Pi : Adafruit Industries, Unique & fun DIY electronics and kits

Vipergrün · 10-23-2013, 07:19 PM

If you just need to point to an NTP server....time.windows.com

id10t · 10-23-2013, 07:41 PM

Quote:

Originally Posted by Vipergrün

If you just need to point to an NTP server....time.windows.com

Yes, as long as you have a (no ports blocked) network connection to the intertoobs there are lots of public NTP servers.

Setting one up on a Debian system (or debian based) is as simple as "apt-get install ntpd"

I'd build one up using a Pi for local access, get to track, set it up, confirm time synch, disconnect from network and just reference the local network one.

djmcmath · 10-24-2013, 02:56 AM

So the trick is that the MacBook itself can't tell time accurately enough once I lose the network connection to the time server. So it'll run as an NTP server, but it distributes a lie. Not quite good enough.

Also, simply setting it to get time from time.windows.com (or wherever) is no good, as I need it to work without an external connection.

Hard drive: your Raspberry Pi option may be the best. I've looked at doing a PPS GPS to get the time signal, but I don't have a serial port to work with on this laptop. (I could get another laptop, and a PPS serial GPS... And that might be as simple...)

But then, if I'm going to build a RP mini computer to get the time via GPS, I could also get GPS on the board. And, while I'm at it, I could pipe the inertial data in as well, and make the itty bitty computer BE the data logger, not just the time server.

Thanks for the idea, Harddrive.