David Taylor over at Satsignal.Eu has done a wonderful article on turning your Raspberry Pi into a Stratum 1 NTP server. A Stratum 1 NTP server is one that is connected directly to a Stratum-0 device such as a GPS. I made an initial device up based one of the Ublox GPS modules from Hab Supplies however with its passive antenna and limited wiring it had to be near a window to work.
Also the MAX6Q GPS modules used aren’t designed for timing applications, however that said I achieved a fairly reasonable level of accuracy of 6ms. I decided to make up a PCB to utilise the proper timing module the LEA-6T this would act as an evaluation board featuring USB for connection to a PC, separate outputs for the PPS and PPS2 finally it would feature a header to permit direct connection to the Raspberry Pi.
Osmocom have designed a PCB which is similar however I have enhanced it a little with a PPS LED, Raspberry Pi header and I changed the regulators as the LEA doesn’t need the larger regulators. Additionally the Osmocom part for the LEA had some very odd solder mask on it and had to be redone.Here you can see the board with an LEA-5S on for testing. Although it looks similar to the Osmocom part the board was designed from scratch this fits on the Pi :The case still fits on nicely (with a little modification!) :
I‘ve released this board as open source and its on Github here. I do have some spare PCB’s free which I can supply to your spec with either a LEA-5S fitted or the LEA-6T. PCB’s are £3.50 , boards assembled with LEA-5S are £40.00 and with the 6T £100.00. Send me a comment if this is of interest, these boards will be built to spec.
A Stratum 1 NTP server for £50 is a bit of a bargin!