This is one of my latest projects, a Stratum 1 NTP server. I found an extremely well written article on how to carry this out, by a chap called David Taylor.
The only change I made was the type of GPS unit I wanted to use. I had already built a lightning radar, which used a GPS unit (EM406A). One of the biggest issue was finding an outdoors housing for the GPS unit, and as I had come up with a solution, I decided to use the same unit.
This gave one interfacing issue with the PI, the 1 PPS, was only 2uS long, not enough for the PI to catch. The solution was to to put the signal through a signal stretcher. I found a NE555 timer kicking around and a few other components, and as you can see from below, the result. The beige RJ45 connector on the veroboard is for the connection to the GPS unit. This makes connecting and disconnecting the unit easy.
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I have allowed plenty of space on the veroboard for an I2C project I'm also going to be starting on soon.
By making the veroboard the same foot print as the PI, means it's very easy to mount the board, no external box needed, A Raspberry PI with a Loft.
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