Tech question: need a low cost NTP server
 

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." :)

Any tiny linux server can be an NTP server.

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

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

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.

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. :)