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Arduino DCF77 library

The DCF77 library adds the ability to read and decode the atomic time broadcasted by the DCF77 radio-station. It has been designed to work in conjunction with the Arduino Time library and allows a sketch to get the precise CET time and date as a standard C time_t.

The library can be downloaded through the Arduino or PlatformIO library manager, or downloaded as a stand-alone package, see the read-me page. Example sketches have been added to 1) illustrate and debug the incoming signal 2) use the library, using the setSyncProvider callback and converting to different time zones. In order to exploit all features in the library, Both the Time and TimeZone library are included.

Additional documentation and full explanations of the samples can be found in these blog posts on DCF Hardware, DCF Signal and ultimately DCF Library

Functional Overview

 DCF77(DCF77Pin, DCFinterrupt, OnRisingFlank); // Initialize
 time_t getTime();       // Returns the current time in CET
 time_t getUTCTime();    // Returns the current time in UTC
 Start();                // Start listening to DCF77 signal
 Stop();                 // Stop listening to DCF77 signal

Using the Library

To use the library, first download the DCF77 library here at

and install it in the Arduino Library folder. For a tutorial on how to install new libraries for use with the Arduino development environment please refer to the Arduino reference on Libraries or follow this step-by-step how-to article on installing Arduino libraries. If the library is installed at the correct location, you can find the examples discussed in this and the previous post under Examples > DCF77. I also added the time library to the archive for convenience.

The DCFF77 directory contains the DCFF77 library and some example sketches

- DCFSignal.pde

  This is the most basic example: it shows the raw signal coming from the 
  DCF decoder. It will show Pulse-to-Pulse times of approximately 1000 ms and 
  pulse widths of approx 100ms and 200ms.

- DCFPulseLength.pde

  This example illustrates the pulse-to-pulse time and pulse lengths 
  coming from the DCF decoder. While the DCF specification says that pulses 
  should be either 100 or 200 ms, you will probably see longer pulse lengths. 
  For optimal distinction between long and short pulses use the output of this 
  sketch to set the parameter #define DCFSplitTime in DCF77.h to (Tshort+Tlong)/2.

- DCFBinaryStream.pde

  This example shows the binary stream generated by the pulse train coming 
  from the DCF decoder and the resulting CET time.

- InternalClockSync.pde

  This is the probably the most important example: It shows how to fetch a 
  DCF77 time and synchronize the internal Arduino clock. 

- SyncProvider.pde

  This sketch shows how to fetch a DCF77 time and synchronize the internal clock 
  using the setSyncProvider function. Note that the loop code does not require any 
  logic to maintain time sync. The Time library will monitor DC77 and sync the 
  time as necessary. 

- TimeZones.pde

  This example shows how to convert the DCF77 time to a different timezone. It uses 
  the UTC time to ensure that no ambiguities can exist. For timezone conversion it 
  employs the TimeZone library.

- Binary DCF77 clock with exponential filter - this example shows how to improve the noise tolerance of the library by means of an exponential filter. It is part of a larger DCF77 project.

Example sketch:

The sketch below implements the most DCF77 basic functionality. It reads the signal from pin 2, and 2-3 minutes it will update the internal clock. More information on this example can be found here.

#include "DCF77.h"
#include "Time.h"

#define DCF_PIN 2                // Connection pin to DCF 77 device
#define DCF_INTERRUPT 0          // Interrupt number associated with pin

time_t time;
// Non-inverted input on pin DCF_PIN

void setup() {
  Serial.println("Waiting for DCF77 time ... ");
  Serial.println("It will take at least 2 minutes before a first time update.");

void loop() {
  time_t DCFtime = DCF.getTime(); // Check if new DCF77 time is available
  if (DCFtime!=0)
    Serial.println("Time is updated");

void digitalClockDisplay(){
  // digital clock display of the time
  Serial.print(" ");
  Serial.print(" ");
  Serial.print(" ");

void printDigits(int digits){
  // utility function for digital clock display: prints preceding colon and leading 0
  if(digits < 10)

On using and modifying libraries

Questions, comments and suggestions on the library and documentation

Forum discussion on DCF77 Library
Forum discussion on Time Library
Forum discussion on TimeZone Library