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A project log for GPS Disciplined xCXO

A DIY GPS disciplined 10 MHz reference clock

nick-sayerNick Sayer 01/31/2017 at 02:530 Comments

I made a little adapter board to take the NMEA output, PPS and 5 volt power from the 6 pin mini-DIN diagnostic connector and connect it up to a Raspberry Pi GPIO connector. That done, I've now made a Pi Zero Stratum 1 NTP server "accessory" for the GPSDO.

So the two share the GPS receiver, and because of that they just have one antenna connection - a nice way to dual-purpose the connection.

The circuit is simplicity itself - just a diode level shifter (to 3.3V) on the NMEA data and PPS line. The Pi serial out line goes through one of the two DIP switches and then to the GPS receive pin of the diagnostic connector. The other DIP switch is a disconnect for the 5 volt power. You can use it as a power switch (so you don't have to disconnect the oscillator or turn it off to power cycle the Pi), or disconnect power entirely and power your Pi separately (this probably would have a positive impact on the short term stability of the oscillator output - how much remains to be seen).

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