2€ charger for any kind of lithium-ion battery

Lithium-ion batteries are everywhere and they are awesome also for hobbyist projects. I’ve been tempted more than once to use old smartphone batteries in my projects, but recharging them might be a problem.

Well, this time I tried my hand at recharging small coin-cells like the LiR2032. I’ve been looking around for commercial chargers, but they seem to be kind of unpopular. Turns out you can do one yourself with less than 2€.wpid-wp-1448223544369.jpeg


The knock-activated noisy box

This project was intended as a prank; when I was thinking about the uses of a knock sensor I thought it would be funny to use it to make a doorbell. The thing you see is a small box that produces a funny chirping noise when you knock or shake it. It is intended to be attached to a door, or some other moving object. Not really an Arduino project since it uses only basic electronic components, but still it was quite entertaining to make and it’s a chance to have fun with analog electronics!

Read ahead to see instructions on how to make one!