Precise timekeeping: keeping track of international UTC time.

The green LED is the DCF77 terrestrial signal received from Germany. On = pulse received; 100 ms (zeroes) and 200 ms (ones) pulses, except on second 59. Protocol described here on [ Ссылка ]. You can even decode the protocol from the video, I have included more than a full minute.

The DCF77 module is similar to this one + electronic components to adapt power and levels to a RS232 interface. [ Ссылка ]
Precision: +/- 5 ms.

The red LED (led off = pulse, 100 ms pulses) is the PPS signal derived from the GPS satellites. The GPS receiver is powered via USB, it's a u-blox NEO-6M basedmodule available here. [ Ссылка ]
Precision: +/- 50 ns.

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