If you’re new to hacking, Halloween is a great excuse to get started, and [Chuck] has put together an inexpensive animated Halloween decoration that you can show off on your front door. After scoring a $5 plastic Halloween doorknocker from Wal-Mart, [Chuck] gathered together a small pile of components and then set about breathing some life (death?) into its scary but motionless face.
Though he opted to use a Digispark, you should be able to use any Arduino that is small enough to stuff inside the plastic head. [Chuck] cut some holes in the eyeballs and glued in two RGB LEDs, then cobbled together a quick-and-dirty mount in the mouth area to hold a small servo. The lights and the servo are wired to the Digispark, which turns the lights on and instructs the servo to slam the ring against the door. It’s is battery powered and currently has only two settings: on or off. This should be good enough to scare the kids for this year, but [Chuck] has plans to add a much-needed motion sensor and sound via a Bluetooth connection.
As simple as this build is, it could be just the thing to get you in the holiday spirit, or to introduce the young hacker in your home to the world of electronics and coding. Check out the short video of the doorknocker after the break, then swing by [Chuck’s] website for detailed build instructions and his Github for the source code. If you’re having trouble finding this doorknocker at Wal-Mart, [Chuck] recommends a similar one on Amazon. Don’t stop now! Make some Flickering Pumpkins too, or if you want a challenge, hack together your very own Pepper’s Ghost illusion.
Off topic, but are those kitten adverts from Supplyframe still in rotation?
I used an arduino once with a piezzo to detect knocks. Could go well with this. Kids knock on the door and the knocker mimics.
Or use a motion detector…
…so it sees you coming and knocks for you!
Easily done with an ultrasonic distance sensor or an IR proximity sensor. Nice and cheap on Amazon and perfect for Arduino projects:
HC-SR04 Distance sensor ($5): http://amzn.to/19xlsmP
HC-SR501 IR Sensor ($6): http://amzn.to/GLHt4w
Also, Dollar Tree has these exact door knockers for a dollar.
I love this project idea, and I have some door knockers coming to me in the mail. I don’t have a regular servo however, I only have a Parallax continuous rotation servo. This servo might be able to work for this project, but this type of servo does not have any position feedback. The sketch I wrote sends signals to tell the arm to start rotating clockwise to swing the knocker away from the door, delay a few mS while the knocker gets into position, then rotate counter-clockwise to swing back toward the door. The problem is, it does not always return to the exact same spot. I am thinking of making some kind of friction clutch so if the servo tries to drive the knocker into the door, it will just slip. With the clutch, I can even tell the servo to rotate toward the door after the sequence to make sure it’s touching. What do you think of this idea? Any thoughts of what materials to use and how to make a friction clutch?
[Chuck] responded to my question on his blog. His suggestion was to add a limit switch to my project instead of a friction clutch. It’s a good idea, now I just need to see if I can find the switch I removed from that old toaster oven’s glass door mechanism…