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."
