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DCF77 is a German VLF transmitting station that broadcasts a time signal across Europe on 77.5 kHz. Thus a common sight in a European home is a clock emblazoned with the words “Radio controlled”. With the timing broadcast in a simple and low speed digital format it doesn’t require the greatest of hardware to decode, and a small microcontroller can handle the task with ease. And there are few smaller than an ATtiny as used in [kwolf1909]’s decoder. It takes a DCF77 bitstream from a receiver, and shows the time on an I2C display.
The receiver isn’t part of this project, however a single-frequency longwave receiver is not a difficult thing to build. The interface is a push-button, for which a short press cycles between display modes and a long press triggers a DCF77 reset. It also supports an external temperature sensor and real time clock module, if you’re using an ATtiny with enough pins.
We like this project; it’s simple and does one thing well, and it’s a welcome reminder that not every device needs a powerhouse of a processor. If you’re interested enough to build your own, we’ve featured someone doing a deep dive into the signal before.
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