Introduction: Blumcaw Cupcake (Blinking, LED, Ultrasonic, Motorized, Cackling, Arduino, Witch) With 3d Printed Parts

Picture of Blumcaw Cupcake (Blinking, LED, Ultrasonic, Motorized, Cackling, Arduino, Witch) With 3d Printed Parts

This old witch has a blinking wart on her nose.  If you step too near (as determined by a Ping ultrasonic transducer), she will cackle out a greeting, her hat will spin and her eyes will flash seven colors.

Blumcaw can be made as a "plain old cupcake" without electronics and 3d printed parts if maintaining sanity is important in your household.

Step 1:

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Let's start by making cupcakes!

Almond Cupcakes


Preheat the over to 350 degrees F and line a cupcake tin with 12 paper cups.



¾ cup softened butter

1 ¼ cup granulated sugar

3 eggs

½ teaspoon pure vanilla extract

½ teaspoon of almond extract

1 ½ cup all-purpose flour

½ teaspoon baking powder

½ cup milk


Put softened butter and granulated sugar into a mixing bowl and cream together with an electric mixer until light and fluffy. Add eggs, vanilla, and almond extract. Blend together. Add flour, baking powder, and milk. Mix until the batter is smooth. Fill a cookie scoop with batter and put batter into one cupcake paper. Repeat process until all of the paper cups are filled. Bake for 20 minutes or until the top of cupcake springs back when touched.

Yield: 12 cupcakes

Step 2:

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I needed a structure to hold the motor and route the wires--also I needed something to fit on the motor shaft and hold the witch's hat.  I made these parts with a MakerBot Replicator--design files here:

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Inside the L shaped tube there is a channel for wires.  At the top end of the L, there is a rectangular hole which holds the motor I am using.

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This is the schematic and parts list for the electronic components.

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Solder wires to the motor.

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Using wire wrap wire, connect the LED's as shown on the schematic (resistors will be outside the cupcake, no need to insert them).

To connect the 7 color LED's, take a look at these instructions:

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Insert the motor and wires into the "L."

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Press the motor into its slot.

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Choose your cupcake and cut a square out of the center for the support tube.

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Turn the cupcake over and cut out a segment to allow passage of the small part of the "L"

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Insert the "L" tower into the cupcake.

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Obtain 7 ounces of marzipan candy dough.  Divide the dough in half.

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Add green food coloring to half the dough.

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When well mixed, you'll have a uniform colored green ball.

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Remove about 1/3 of the ball and divide that into two elongated pieces.

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Using a nut pick, hollow out the inside of the "nose."

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Poke a hole through the nose for the "wart LED." 

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Take the main green ball and hollow out the inside.

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Poke a hole in the main green ball and join it to the "nose hole" on the nose.  NOTE:  these holes are needed for wires, they are not needed for a witch without electronics.

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Add the "lower jaw" piece below the nose.

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Shape the mouth using the nut pick.

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Take a small ball of marzipan and mix in yellow food dye.

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Make a few small spheres.  Two will be for eyes, the others for teeth.

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Add eyes.

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Add teeth.

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This is a little gross, but the electronic version needs holes in the eyes where LED's will eventually be.

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Make purple dough using red and blue food coloring.

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Make a flat coin type piece and a hollow cone for the hat.  Bend the tip of the hat over.

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Assemble the hat.

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Create a yellow "snake" and put this band around the hat.

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Make a couple of "mean" eyebrows.

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Put magnet wire (or string) through the nose and eye holes.  This is "pull" wire to assist in getting the LED's into place.

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Pull the LED's into place.  This is a challenge, even with two people working.

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Add the hat base to the end of the motor shaft.

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Put some marzipan in a garlic press.

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Squeeze, and you have lovely hair.

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Add hair.

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Time for some frosting:

Butter Cream Frosting  (for witch’s purple collar)



1 lb. of 10X confectioner’s sugar

1 stick of softened salted butter

¼ cup milk

2 teaspoons real vanilla extract

red and blue food coloring


Using an electric mix, cream ingredients together until frosting is smooth. Add 6 red drops of food coloring and 4 blue drops and mix together for purple frosting.


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Pipe the frosting onto the cupcake.

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Finish with the frosting and add hair as desired.

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Place the hat on the rotating disk.

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Now, we need to load a "sketch" (software) into the Arduino. Note the "if duration <4000" line below--the "4000" is the number that determines how close you must be to the Ping ultrasonic sensor to trigger the witch.  Change this number if you want a different minimum activation distance.

const int pingPin = 7;

long duration;

int ledPin = 13;

int eye = 5;


void setup ()


  pinMode (ledPin, OUTPUT);

  pinMode (eye, OUTPUT);



void loop ()


  digitalWrite (ledPin, LOW);

  digitalWrite (eye, LOW);

  delay (10);

  pinMode (pingPin, OUTPUT);

  digitalWrite (pingPin, LOW);

  delayMicroseconds (2);

  digitalWrite (pingPin, HIGH);

  delayMicroseconds (5);

  digitalWrite (pingPin, LOW);

  pinMode (pingPin, INPUT);

  duration = pulseIn (pingPin, HIGH);

  if (duration <4000)


    digitalWrite (ledPin, HIGH);

    digitalWrite (eye, HIGH);

  delay (10000);




  digitalWrite (ledPin, LOW);

  digitalWrite (eye, LOW);



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Remove the "play" switch on the digital recording module and solder two small (wire wrap wires) wires on the traces that the switch connected.  A contact from the relay will activate the play mode.

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Wire it all together--as in the schematic in step #4.

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She's not a thing of beauty, so any mistakes just enhance the final product! 

I added this video so that technically curious people could see the entire system in operation.  Sensitivity range is around two feet for triggering the cupcake.

Special thanks to my wife for marzipan work and wire pulling :)


The Steph Show (author)2012-09-28

Awesome! You've got my vote!! :)

Kitana Kellaway (author)2012-09-27

It's food with a crunch lol

susanchen2011 (author)2012-09-27

It is very creative.

iceng (author)2012-09-26

Very cool  sweet....:-)

Our toys are the best engineering.


jessyratfink (author)2012-09-26

Hahaha, love the flashing wart on her nose. Excellent!

About This Instructable




Bio: I am an author and a maker. My current project is Santa's Shop. I'm working on a science fiction type book--more later. @EngineerRigsby
More by MikeTheMaker:Santa's Shop 2017, the TrainSnowflake Gear WreathHappy Gear Table
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