Here’s a neat AVR based LED clock you can make, all the plans and software are released under the GNU GPL.

It is a clock with a big display unit, that has a DCF77 (german timesignal) Receiver and can be connected to an ethernet network, where it can serve as a NTP server. All of this based on an Atmel AVR microcontroller with 8 KB flash.

NTP DCF77 LED Clock – – Link.

20 thoughts on “AVR LED Clock

  1. robopony says:

    How did they wire up the MAX7219 to drive the LEDs around the perimeter? It seems like it would be a huge pain to get a seven segment display driver to do that.

  2. robopony says:

    Ahhh, after a quick glance at the data sheet, it looks like you can set the MAX7219 to non-decoded mode, where you have access to each led. Nice!

  3. jachim says:

    Great clock! I’ve just started thinking about making a clock, and this will be a huge leg-up. Is there a US equivalent of the DCF77? I’ve been looking at DigiKey’s website, and will check their catalog tonight, but so far I haven’t found anything.

  4. Windell_Oskay says:

    jachim> The US equivalent of DCF77 is WWVB, broadcast from Ft. Collins, CO. (It’s a radio station, not a chip.)

  5. jachim says:

    Windell (Hi!): I guess I should have said “US equivalent of the DCF77 _receiver module_” he used in the project. I spent a good hour or so last night looking for one, but any that I did find seem to be discontinued. The most promising one looked to be a Temic chip, which seems to have been bought by Ateml (!), but their website doesn’t seem to know anything about it.

  6. =mathew says:


    “Waa! It’s a bomb!”

    (I’d also be interested in a WWVB chip…)

  7. Windell_Oskay says:

    WWVB protocol is pretty straightforward. Early WWVB clocks had decoders wired on TTL logic chips– a book that I have (Don Lancaster’s TTL Cookbook, from 1974) shows you how to do that. But it’s a pain, and you won’t find any modern chips dedicated to it because it’s almost trivial to do with the smallest microcontroller. Ask Google: someone has probably done it for your flavor of MCU already.

    The good “hacking” solution about how to get a WWVB decoder is to take apart a cheap ($10) radio-controlled clock movement and intercept the signal that drives the “ticking” motor. You can read more about that here. I tried to do this for my nixie clocks, but did not consistently have good luck with the receivers, so if I were to build more WWVB clocks, I would definitely go for the MCU approach.

  8. jachim says:

    It is my plan to use and Atmel AVR also. I did some more searching just now, and it looks like the receiver module used in this project would work, it would just need an antenna tuned to 60 kHz. I’ve also found this module that will output the BCD time code data. This is all I was looking for, I’m looking forward to the challenge of writing a program to decode the data.

    Reading the web page and datasheet was what led me to believe the unit described in this project would also work for WWVB. The only changes for the different frequencies is to pick/design an LC network that resonates at the desired frequency. Time to relearn all the stuff I forgot when I was a EE major/studying for my Ham license.

  9. Josh says:

    I’m actually working on a WWVB AVR contolled/decoded clock right now.

    I’ve got everything working except for the decoding of the WWVB signal – mainly because here in NY the signal is super-weak and highly directional.

    I got my WWVB -> serial converter from here it’s called the cmax CME6005 – they even sent me some free pre-calibrated antennas and 60hz oscillators. Actually, the whole thing was free because I’m a student and it has to do with my research project =).

    Anyhow, if I get this running, there’ll be a post on instructables for sure =)

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