There aren’t much details on this Spooky Automatic Halloween Door Knocker project by WAGfilms. But just by looking and his brief description we can get enough info to build our own. I think this is a great project idea that can be used for more than just a cool Halloween prank. He is using an Arduino Pro Mini as the brain of the system and it runs off some AA batteries. We can see that there is a PIR motion sensor that has been mounted in the forehead of the beast which will is ideal to send a signal to the arduino that someone has arrived. Some spooky LEDs are used to make the eyes glow using a nice smooth but quick ramp on. This can be done using one of the PWM pins on the microcontroller. But the best part is the automatic knocking of the door! Stick a servo motor in there and connect it to a single spare I/O of the controller and you are done. The servo will need to be quick large depending on the weight of the knocker though since it needs to move it quite vigorously!Â