Arduino DCF77 radio clock receiver – Library

(This is part 3 in a small series on using DCF77 for accurate time keeping with an Arduino. You can find post #1 here and post #2 here)

Before we start to look at the library, let me start by saying that this is by no means the first Arduino DCF77 decoder. In fact, a large part of this library is based on the sketch made by Matthias Dalheimer. I did not intend to write a new library, but because of the noise spikes I was picking up, I started rewriting parts to make it work under noisy circumstances and, as these things seem to go, ending up writing a whole new library.

Because of the noise I added, besides the spike rejection, some checks on the decoded time. Furthermore I made made another major change in the code: The class library attaches an interrupt function to the DCF77 pin, which fills a buffer with the received bits. This interrupt-driven part is made to be quite lightweight, while the hard work (checking parity, calculating time, doing a few sanity checks) is done in the code called from the main loop. But because the interrupt driven loop fills the buffer (and starts filling a new buffer after that), so there is no real hurry in the main loop to re-enter the getTime function.

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

A zipped tarball of the version as well as older versions can be found here.

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 following website: http://www.arduino.cc/en/Reference/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 archiver for convenience.

Below is a demonstration of how the library processes the binary data and returns a time and date. In order for the example to give output on the binary stream make sure that logging is turned on in the DCF library. You can do this by adding the #define VERBOSE_DEBUG 1 in Utils.cpp.

I get the following output:

After the first full cycle we get the feedback “time inconsistent” because:

1. The difference between the DCF77 time and the internal time (still close to 0 -which translates to a date in 1970-) is too big
2. The difference with there is no previous DCF77 time measurement is too big because, well, there is no previous measurement.

After the second cycle there is a previous measurement and both measurement points are consistent, and we get our first DCF77 time. Success! Note that the time queried with DCF.getTime() is compensated for the period between receiving the time from the receiver and the moment that it is queried from the library.

Now, let’s try an example that actually updates the internal clock time. For this example the output I turned logging off.

Resulting in the following output:

Finally, that kind of wraps things up. However, I want to demonstrate one last thing. I used the Time libraryquite a lot in the library, but it also has a feature that is you can nicely use in your main program.

 

Below is an example sketch showing how to use the syncProvider functionality to simplify the sketch code. Note that the loop code does not require any logic to maintain time sync and even the getDCFTime function could be removed to make the code even more concise. The Time library will automatically monitor DCF77 and sync the time as necessary.

ps. After writing this library I discovered another Arduino DCF77 class that is based on the code of Matthias Dalheimer at http://fiendie.net/arduino/funkuhr. I haven’t tried it, but the code looks quite clean, so give it a shot.