{"id":345,"date":"2021-08-04T14:16:53","date_gmt":"2021-08-04T12:16:53","guid":{"rendered":"https:\/\/automatico.freevar.com\/?page_id=345"},"modified":"2021-12-17T10:38:56","modified_gmt":"2021-12-17T09:38:56","slug":"dcf77","status":"publish","type":"page","link":"https:\/\/automatico.freevar.com\/index.php\/arduino\/dcf77\/","title":{"rendered":"DCF77"},"content":{"rendered":"

\"\"DCF77 refers to a communication protocol that allows the time of a system to be synchronized with that propagated by a radio transmitter near Frankfurt (Germany).<\/span> The signal is transmitted with the frequency of 77.5 kHz and a power of 50 kW.<\/span><\/span>
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On the side we see the range of the signal that reaches 1900 km during the day and 2100 km at night (with better radio signal propagation) (source Wikipedia).<\/span> <\/span><\/p>\n

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\"\"The signal is encoded by modulating the carrier wave with the ASK (Amplitude Shift Keying) method.<\/span> The first line of the drawing illustrates a series of logic levels representing the bits, the second line is the carrier wave, the third is the amplitude modulated carrier in ASK.<\/span> This kind of modulation is very sensitive to noise and is no longer used in current equipment.<\/span> The side drawing is not to scale, in fact the modulation depth varies between 100% and 20%.<\/span><\/span><\/p>\n

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\"\"<\/a>The radio receiver is a very simple circuit composed by a ferrite antenna and an electronic circuit tuned to the transmission frequency of 77.5 kHz.<\/span> The signal output from the receiver is like\u00a0 shown beside.<\/span> One bit is transmitted every second: 0.9 seconds high and 0.1 seconds low means bit 0;<\/span> 0.8 seconds high and 0.2 seconds low means bit 1.<\/span><\/span><\/p>\n

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I didn’t buy the radio receiver, but I got it from an old radio controlled electronic clock.<\/span> The DCF77 output circuit provides a signal with inverted electrical levels, so I had to build an electronic signal inversion and electrical level adaptation circuit, with a bc547 transistor, to condition the signal and thus adapt it to the input of an Arduino nano.<\/span> <\/span><\/p>\n

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Here is the result after a night of waiting.<\/span> I put the circuit outside the house towards the north and powered it with a battery.<\/span> <\/span><\/p>\n

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Now let’s see how the software is structured.<\/span> Mainly the program uses four libraries:<\/span> <\/span><\/p>\n