Casually put together a small but rather fun project. I got curious about how much power my DIY gadgets actually consume—and at the same time, I wanted to check the real capacity of those AliExpress batteries. Sure, you could use a multimeter, but then you’d have to rig up some janky setup to wedge it into a USB cable, plus keep unplugging it whenever you need it elsewhere. And devices with microcontrollers have fluctuating power draw depending on their operating mode. So I built myself a dedicated device.

A small device based on the MH-Z19B sensor has been sitting on my desk for years, quietly reminding me when it’s time to open a window and let some fresh air in. Its design is… well, not exactly elegant, but the utility more than makes up for any aesthetic shortcomings.

I built an FM radio receiver. As usual, the goal was to “build something useful and learn something new along the way.” What made this project especially exciting was that it involved working with an STM32 microcontroller—something I hadn’t done before, even though I’ve had several dev boards and programmers lying around for years. I also really wanted to use the headphone wire as the antenna, just like in commercial devices.

Our company suddenly changed its vacation policy: unused days from the previous year now had to be taken by the end of January. So I had no choice but to take time off. Naturally, I went to the sea. The North Sea, to be precise. Luckily, it’s only a three-hour drive from where I live. The North Sea in January — it already sounds like a ballad of adventure and wandering.

I built another clock. Not because I don’t already have clocks—I have plenty, including a few homemade ones. But if you start some big, complicated project, there’s a good chance you won’t finish it… even if you’ve got the long New Year holidays ahead.

If you head south from Cologne on Autobahn A1, about 30 to 40 kilometers in, there’s an exit toward the town of Bad Münstereifel. It’s a small, picturesque town tucked between forest-covered hills. A fairly lively river called the Erft flows right through it.

In my DIY projects, I frequently utilize lithium batteries and TP4054 chips to charge them. Charging current for a battery should not exceed 1 °C (capacity multiplied by one hour). At this rate, the battery will charge to full capacity in precisely one hour.