Easton Elliott made this 4000-series CMOS 24-hour clock as a final high school electronics class project. Rather than using a MCU he chose to use CMOS IC’s including a 4060 and 4013 to generate the 1Hz signal. The writeup and documentation can be found on Easton’s geekness website.
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Hah, I’m enthused that my blog post has become this popular! I feel embarrassed enough of my wiring.