I have long wanted a GPS receiver that is either integrated with an NTP server, or compatible with a device like a Raspberry PI, including PPS signals.
Until a few years ago, you could only go buy an integrated unit for $2000-$6000, including an oven controlled crystal. While this is appropriate for a large enterprise server, I'm wanting one for home use.
More recently, I have found $300 units.
What I am looking for is a $15 to $35 (or maybe to $50) unit. Any suggestions?
The purpose here is to run a stratum 1 NTP server. This would then provide time to all my computers. I would like NTP precision of at least 15 (30 microseconds). 19 or 20 (2 or 1 microseconds) would be better.
I am expecting I will have to assemble something with a Raspberry PI or Beagle Bone, but would prefer a prebuilt unit if anyone knows of one.
Obviously, a serial interface will not get that precision, but the PPS interface can. PPS is pulse per second, a once per second microsecond precise pulse usually connected to an interrupt on a host computer (or ignored if you don't care about time precision).
It would be nice if adafruit hadn't decided to only support one expensive GPS.
It would be nice if there were a SOC including a CPU and GPS, so the CPU could read the GPS time registers directly. That might achieve an NTP precision of 26 (16 nanosecond or about 5 meters).