Electronics : Atomic Clock DCF77 interface

I use this circuit to provide my electrical home installation (Nikobus) with an atomic clock. The coupling between the DCF interface and Nikobus is done by the 05-200 PCLink module.

DCF77 :

DCF77 is a radio station in Germany. This radio station sends a time signal that can be received in large parts of Europe. The signal is an amplitude modulated pulse with a frequency of 1Hz. A complete time signal is 60 pulses long, so 1 minute. A pulse length of 100ms is a logic zero, a length of 200ms is a logic one. The start of a minute is marked by the absence of the 59th second pulse.

Composition of the DCF signal

Bit 0	= minute sign
Bit 1 - 14	= reserved
Bit 15	= 1 if spare antenna is in use
Bit 17 - 18	= 01 during the winter time, 10 during the summer time
Bit 19	= leap second warning
Bit 20	= start of the time message (always 1)
Bit 21 - 24	= minute entities
Bit 25 - 27	= minute dozens
Bit 28	= parity check bit 21-27
Bit 29 - 32	= hour entities
Bit 33 - 34	= hour dozens
Bit 35	= parity check bit 29-34
Bit 36 - 39	= date entities
Bit 40 - 41	= date dozens
Bit 42 - 44	= day of the week
Bit 45 - 48	= month entities
Bit 49	= month dozens
Bit 50 - 53	= year entities (00..99)
Bit 54 - 57	= year dozens (00..99)
Bit 58	= parity check bit 36-57
(Bit 59)	= absent pulse; marks the end of a minute

Every DCF-clock can work without the DCF signal. The clock will then use the internal crystal. If the DCF signal is received afterwards, the clock will automaticly synchronise with the DCF time.

Schematic :

Circuit :

The DCF interface is a complete module from Conrad with order code 641138 - 8A. This module needs a DC supply voltage between 1,2V to maximum 15V. The DCF output signal is inverted and non inverted available. These outputs have a maximum output current of 1mA. I used the inverting output of the Conrad module. Due to the current limit of 1mA we need an extra buffer stage. This buffer is made by R2, R3 and Q1. The DCF signal is available between X3 and X4. The 8V output of the beltransformer inside the electrical cabinet provides the AC power supply. The power supply is very simple, with the 7805 we create a 5V DC voltage. Because you can build the circuit on a piece of stripboard there is no PCB available. It's best to place the antenna facing east.

In use :

Schematic and PCB design :

You need the Eagle CAD program to view this schematic. Download a limited edition of this program at : Eagle Soft USA

Project : DCF interface

Sources :

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Content - Electronic circuits,projects and schematics : DCF interface - Stego