Check out this distance sensing Halloween prop designed to spook the willies out of trick-or-treaters.

As we approach the end of October, the spooky Halloween energy is starting to find its way into my world. I’m not much of a Halloween-er myself, but I have always felt that Halloween is an excellent excuse to show off your killer maker skills, creativity and maybe even scare some folks. This week I made a little interactive Halloween decoration that activates when someone walks by.

My Interactive Spooky Halloween Cat consists of a plastic skeleton cat I found at Michaels and an enclosure that I laser cut from black acrylic. Inside the enclosure is a SparkFun BlackBoard as the brains of the project, an Ultrasonic Sensor for distance sensing, a Qwiic MP3 Trigger Board to add some hissing sound effects, a small hamburger speaker for the sound, a small servo motor to create motion in the cat’s jaw, 16 WS2812 LEDs to create the red light and a small breadboard to make the circuit building quick and easy. A full list of parts used in this project can be found here.

Let’s take a look at how this project interacts with the world around it. When a user enters within 100 cm of the ultrasonic sensor, the skeleton and eye sockets light up, it makes a loud, angry hissing sound, and the jaw begins moving up and down.

In order to accomplish this interaction (in addition to the circuitry described further down), the servo motor is connected to a clear strand of fishing line tied to the bottom of the cat’s jaw bone, so when the servo pulls back, the jaw opens up. I also added some white elastic tied to the top and bottom part of the jaw, kind of like a rubber band on braces, ensuring the jaw closes when the servo pushes back forward. I cut small sound holes in the enclosure above where the speaker is to get the best out of the sound.

I also made some modifications to the WS2812 LEDs. First, I cut two individual LEDs from the strip and soldered them together with hook-up wire at a distance of about one half-inch. Then, I connected these via hook-up wire to the remaining 14 LEDs on the rest of the strip. I unscrewed the cat’s skull to remove it from the body and open it up, then carefully drilled holes in the eye sockets, behind which I glued my two individual LEDs. Then I put the head back together and onto on the rest of the skeleton. Finally, I carefully hot glued the remainder of the LEDs down the inside of the cat’s spine.

Below is a photograph of the circuit I used in this project. Because some of the parts I used are not available for frtizing diagrams, and because it is hard to see all the connections, I created the table below the image to outline each connection used in this project.”