The clock, which is made from 25 CD4000 ICs, three 555/556 ICs and a handful of discrete components, includes an alarm and a way of setting the clock that until now I have only seen implemented using microcontrollers. All this makes for a rather involved circuit, but I have split the schematic into a number of pages, which will hopefully make it easier to follow
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The timebase is similar to many other clock designs published on line, but that`s because this is by far the best way to do it. A standard 32. 768KHz watch crystal is connected to the internal oscillator of a 4060, the output of which is divided down to 2Hz by the 4060`s 14 binary divider stages. A final divider stage, made from one half of a 4013, gives a 1Hz signal which is used to run the clock. The timebase has two 1Hz outputs, one of which is always on and the other of which is gated by the RUN signal. This output is only enabled when the clock is running, stopping the clock whenever it is being set. The ungated output is used to make the display flash when the clock is not running. The two diodes and resistor to the right of the schematic form an AND gate, which is used to gate the 1Hz signal. Most of the AND gates and all of the OR gates in this clock are built out of discrete components, rather than ICs. Not only does this save board space, something which I would have run out of if even one more IC was needed, it also allows the gates to be put exactly where they are needed, saving wiring. At this point I should probably explain how you set the clock. Many digital clock designs on the internet simply have buttons to increase each digit, or a switch which makes the clock run faster. Instead, I chose to use a method that I have only ever seen implemented with a microcontroller. The clock has three setting buttons,...
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