Halloween is a day when weird and scary things are welcome. So Kyle had this idea to make a knock box which would respond to knocks. Circuit is pretty simple and straight forward – Attiny85 microcontroller detects knocks by using piezo sensor. To make it reliable, he amplified piezo sensor signal by using MOSFET.
Knocking back part is made of DC motor with shaft attached. Knocking pattern is recorded by using microcontroller timer. There are several modes preprogrammed for instance if 13 knocks are detected, then it plays “Adams Family” song using same piezo sensor as speaker. If 20 knocks are detected then box knocks randomly for 30 seconds. Otherwise box simply knocks back same patterns. A special attention is paid to box look. Lego skeleton and chains look great on it.