All the details of the design and how it works are available in my little electronic project's GitHub Repo (it is basically my open lab notebook, with a catalog of many projects now).

Here's a demo of it running a 5-minute countdown (I would be surprised if anyone watches the whole thing without skipping to the end!)..

There's a few things I set out to achieve:

  • the 3x7 displays minutes in two digits, and tenths of minutes on the 3rd digit
  • the Pomodoro countdown runs from at most 95 minutes, but default to start at 55 minutes (my preferred time block)
  • the microprocessor measures reasonably accurate time for the countdown, but I'm not going to be upset if it is a little off (less than a minute)
  • before starting the count, two buttons can be used to increase or decrease the countdown respectively, in increments of 5 minutes
  • when the countdown has completed, the unit will flash for a period of time
    • a button press resets the app for another countdown
    • if no input, go to sleep
  • if sleeping, a button press wakes up and resets the application