About two years ago I got a hold of a basic electronics kit: resistors, LEDs, buttons, a breadboard, etc. Looking at the components, I had no idea what any of them did, let alone how to use them; and I was very much intrigued. I knew what a resistor was in theory, of course, but how one uses them—no idea. So, in my evenings after work when the rest of my family went to bed, one by one I'd reach for a component and learn anything I could about it. A few months later, a notebook filled with formulas and notes on the basics, I thought I needed a goal—a project that'd motivate to learn more. This is that project. A countdown timer. What could be simpler? Or so I thought!

Of course, if the project is to be real it needed to be useful. So: battery powered (two AAs), multiple month-long countdowns in a year without replacing those batteries (low power using STM32L010), accessible (tactile rotary encoder and buzzer along with LEDs). Those were the requirements to start.

Here's what the first prototype looked like:

So, if you really want to get some practice with soldering, I can recommend soldering 110 LEDs in a charlieplexed configuration. By the end of the over 300 solder joints (which took me about a week), you feel a lot more confident.

Anyway, it was a ton of fun and now the next step is to make it more real with a properly manufactured PCB.