Use of the Rockwell "Jupiter" GPS module simplifies the circuitry by using it's 10 KHz output instead of the more common 1 PPS. The
price to be paid is slightly reduced performance. There is no capability for "hold-over." When the GPS signal disappears, so does
You are left to your own devices to determine the suitability of the GPS signal, but my circuit posted here might suffice:
Another simplification is the use of a Microchip 12F629 to perform the "divide by 1000" that is usually done with three decade-counter chips.
One 8-pin DIP package replaces three 14-pin 74LS90 chips. Source and HEX code for programming that chip can be provided.