Edgar implemented capacitive touch sensing using an ATTiny4 to create a touch paddle for Morse code:

Tiny CW Capacitive Touch Paddle

Like many no-code operators, after being on the air for a while, I developed an interest and appreciation for Morse Code [..] I purchased a cheap paddle, but I found the clicking noise a little bit annoying.

The goal of this project was to create a single PCB with an ATTiny4 AVR, a battery, transistors and a 3.5mm connector jack. The paddle is designed to have exposed conductive material in order to read the capacitive touch.

The under 1kB binary code worked well and without error. This made me wonder how small I could make this code. After optimizing the code, I managed to shrink it to under 512 bytes.