DCF77

DCF77 is a time signal broadcast on 77.5kHz by a radio transmitter located att Mainflingen near Frankfurt. The range is such that it should cover nearly all of Europe.

It works in a very similar way to Time from NPL (which broadcasts from the United Kingdom at 60 kHz).

The DCF77 modules that you can buy are generally simple radios. Give them power, and they return a single digital signal. This signal contains one pulse a second (with a double-length pulse every minute), and the length of the gap between pulses signifies a 1 or a 0. This allows for 60 bits of data per minute (details on Wikipedia).

Functionality is provided by the DCF77 (About Modules) module.

Wiring Up

There are several different types of module, so please check with the seller of your board for the exact connections and power requirements. In the board pictured above, the connections are:

Pin numbers are not marked on the board (and similar looking boards have pins in different locations), so you'll need to use a multimeter to check which pin is GND (by checking against the negative side of the board's capacitor).

Software

Just use as follows (assuming you've connected the Data pin of the DCF77 receiver to B3):

require("DCF77").connect(B3, function(err, date, info) {
  if (err)
    console.log("Invalid time received: " + err);
  else
    console.log(date.toString(), info);
});

The callback will be called every minute (assuming a good signal has been received). If there has been a decoding error (for instance parity doesn't match) then the error will be returned. Otherwise err will be null and date will be a Date object.

When Date is valid, info will be an object of the form:

{ 
  CEST : boolean,  // Central European Summer Time
  CET : boolean   // Central European Time
}

As this is radio, things can get corrupted. If two bits of the signal are wrong then the parity can still be correct and your callback will be called with the wrong Date object and no error - to ensure an accurate time signal we'd suggest storing the previous two minutes' Date values, and only updating the time if all 3 dates are consecutive: eg 13:35, 13:36, 13:37.

Using

(No tutorials are available yet)

Buying

You can buy DCF77 modules separately, but they tend to cost around £10 each.

• eBay
• Conrad
• pollin

You may find that it is in fact cheaper to just buy a DCF77 clock, dismantle it and remove the radio (which is usually a separate module).