So for my next project, I decided to make a candy bowl for our library's MakerSpace! I wanted to make something Halloween themed that demonstrated some of the capabilities of the Arduino UNO. The basic idea is that when someone goes to grab candy, the book will close shut on their hand. I used a capacitive sensor, an Arduino Uno, and a micro servo to get this effect. If you'd like to get a better sense of the project, I made a YouTube video where I go through the steps of my design process.
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Step 1: Materials
For this project you will need,
- 1 old book you can part with
- A hot glue gun and standard craft glue
- An X-ACTO knife or boxcutter
- An Arduino UNO
- Freezer Paper
- Tin foil
- A 10 mega-ohm resistor, or ten 1 mega-ohm resistors
- A servo or micro servo
- Ribbon or string
Step 2: Preparing the Book
Okay, so now that you've gathered your materials we can start the project! I started by gluing the edges of the book, because I wanted it to be rigid. First, I put some freezer paper in the book where I wanted the book to open. Next, I used a mixture of 1 part water and 2 parts Elmer's glue which I rubbed all around the edges of the book. After that I put some weights on top of the book so the pages would compress together nicely. I'd suggest using more Elmer's glue in your mixture, because my pages fell apart later on. Let your book dry over night.
Step 3: Cutting the Book
Now that your book is dry, we can start cutting it. I used a box cutter to cut around the edges of my box. After a couple passes I peeled as much paper as I could out. This step took about an hour, and it certainly made a mess. By the time I got to the bottom of the book I had a lot of excess paper still stuck to the edges. Fortunately, I managed to clean most of it out with an X-ACTO knife.
Step 4: Circuitry and Wiring
The circuitry involved in this project was fairly simple. I used the Arduino CapSense library (you can find it here http://playground.arduino.cc/Main/CapacitiveSensor?from=Main.CapSense). Basically all you have to do is wire your resistor between 2 pins on the Arduino, and then attach your foil sensor somewhere along it. I used an if then statement to detect when a hand was over the foil, then I moved the servo to 180 degrees in order to close the book. You can hot glue your foil to the bottom of the book, and tape or solder a wire to it. Since my pages were coming apart already I cut a slot in the side of the book for the servo wire to go through.
Step 5: Decorations
There are a lot of ways you could decorate this book, but I went with a felt "Monster Book of Monsters" design. I covered the cavity of the book with felt (mostly to cover the edges), but I also used it to hide the foil sensor. Then I hot glued felt and googly-eyes to the outside of the book to make a faux binding and cover. Then, I cut teeth out of white felt and glued them to the front of the book. I cut them out of the same square of felt so they would fit together when the book was closed. Next, I glued the micro servo inside the cavity, make sure you use a lot of hot glue when you do this because the micro servo will be holding the book open. Finally I glued the ribbon to the top of the book and the servo horn. You'll probably want to fiddle with the servo and the length of the ribbon until you get it to balance just right. Be careful when you do this step, I ended up burning myself a couple times.
Step 6: Add Candy!
The most important part of this Halloween trick, bait! Most types of candies will work nicely, except full bars. I wouldn't suggest using those unless you get a very large book. Instead please send them to PO Box 1007 Mountain Drive, Gotham City.
An added benefit of this candy bowl, is that kids are less likely to get greedy once they've been surprised by it!