Touch timer

This is a small low-cost touch-controlled timer. It is the most simple but funny project I have experienced and I am still using it today for timing.

The touch-controlled function is implemented purely with code and the characteristics of MCU pins. I used the 2.54mm pin spacing of the digital display and the MCU, directly soldered the hardwares together, without using integrated circuits. One pin of the MCU is set as an output with a high voltage level. When we touch it with our hand, as the human body conducts electricity, the adjacent pin also turns into a high voltage level. The MCU detected this change in voltage and recognized that we had pressed it, thus achieving touch control functionality.

Choice of hardware: STC12C5A32S2 (enhanced version of 51 microcontroller) (¥4); LG5643 (common positive) (¥2.3); Passive buzzer (SMD) (¥2.3); 12MHZ crystal (column) (¥0.1); Battery pack (4.5V) (¥1.7); 3 1.5V batteries (¥6); Total cost less than ¥20.