Now that the clock hardware is working, I can add a lot of functionality just by coding.
It didn't take long to modify the code from my previous blog post to make it display a proper time value, and to make it into a countdown timer.
At this point the timing is not accurate. To make that happen I will likely have to use a timer interrupt at least in main(): the for loop around the clock_show_time call should be something like "while waiting for the interrupt timer" with the interrupt timer set to 1 second.
And I might have to increase the cpu speed to make that possible.
And then I really need to figure out the buttons so that the time can be set by the user.
And crazy wires. it needs crazy wires. And maybe a motion detector...
The updated code has been attached.