To introduce my oldest son to robotics and programming I thought it would be a good idea to build an Animated Grim Reaper for Halloween. I wanted to construct it as inexpensively as possible so I used cheap parts from the local hobby stores and scraps I had around the house. For the electronics I selected a microcontroller, servos and other essentials that I already owned. To keep costs down I also made use of an Andriod app called Arduino Actions by BlueAct. This allowed the microcontroller to send a command via BlueTooth to an Andriod device running the app. One of the actions the app supports is to Play Sound. So I loaded the sound track onto the Android device and created the Play Sound action. It worked great. To see one of the test videos check out this link https://www.youtube.com/watch?v=ohhMNel8JPk
Step 1: Supplies
1) Find an inexpensive skeleton with a movable jaw or as in my case a "bag of bones"
2) 2 LEDs
3) 2 1k ohm resistors
4) A ping sensor
5) 2 servos
6) Arduino Uno
7) Bluetooth device
8) some wire
12) Assorted servo horns
13) Toy Ax
15) Batteries or other external power supply
16) Black Material (to make a cloak)
Step 2: Tools
2) Needle Nose Pliers
3) Soldering Iron
4) Electric Drill
5) Assorted Drill Bits
6) Phillips Screwdriver
8) Android Device
Step 3: Step 1
a) Take the skull and cut the back portion of it off to allow you access to the inside.
b) Attach the front portion of the skull to a scrap piece of wood in roughly the area of the neck (I used an old 1" dowel rod).
Step 4: Step 2
a) Drill 2 small holes inside the eye sockets roughly 1/8" in diameter (depending on the size of LEDs you bought) so the LEDs can be mounted later.
b) Drill a 1/16" hole in the jaw.
c) Drill a 1/8" or larger hole in the bottom of the skull just above the previously drilled jaw hole. This hole will be used to allow the linkage access to the servo.
d) Hot glue 1 of the servos to the inside of the skull such that it is above the 1/8" hole and aligned so that it will not bind when moving the jaw (this step is all about trial and error).
Step 5: Step 3
a) With some addition scrap wood construct the torso.
b) Attach another servo horn to the bottom of the neck.
c) Add the second servo by attaching it to the servo horn and gluing it into the torso.
Step 6: Step 4
a) Begin assembling the electronics by creating circuits from the Arduino to the breadboad as shown in the provided schematic.
b) Add the 1k Ohm Resistors in series from the pins on the Arduino to the positive side of the 2 LEDs.
c) Attach the negative sides of the 2 LEDs to the common negative on the breadboard.
d) In addition to following the manufacture's directions for connecting the servos please attach the 2 servos positive leads to external batteries so as not to burn out the Arduino. The number of batteries necessary depends upon the specification of the servos selected.
e) Attach the external batteries negative leads to the Arduino and breadboard so as to have a common ground.
f) Attach the ping sensor according to the manufacturer's directions. We bought a toy knight's shield from the local dollar store to conceal the ping sensor. We installed the shield under the cloak allowing just enough of a gap in the cloak so as not to interfere with the ping sensor. It blends in so well that hardly anyone notices it.
g) Attach the BlueTooth device according to the manufacturer's directions.
Step 7: Step 5
Write the source code needed to detect someone or something approaching, play the audio via the Android device, and control the servos.
Each particular setup will require changes to the individual servo movements as well as the rest states between movements. This is due to the individual audio track selection as well as the specific placement and types of servos used in the project. For me it was just trial and error to get these settings as accurate as possible.
You may also have decided to use different pins than I did so you'll have to adjust the source code accordingly.
Step 8: Step 6
On your Android device download the BlueAct app (Arduino Actions).
Save the audio file you wish to have your Grim Reaper play on the Android device.
Follow the instructions on how to setup the BlueAct app at https://www.youtube.com/watch?v=RQhx6qBElVk