I made the scariest pumpkin ever! Nothing gory or disgusting, just something that will scare the kiddies and hopefully score me some candy. How? Well, I am glad you asked. I rummaged through my parts bins and came up with an idea. What if I connected a horn to an Arduino and let out a nice blast when someone came around trick-or-treating. Hopefully they are so scared they drop their bag-o-candy and run away, leaving me with plenty of treats.

Note: The key to this project is the delay. You could just wire the horn to the button and I am sure you would get a lot of people to jump. Add a delay to the horn and when they turn their back, the real fun begins! Honk!

You can find this build on the MAKE blog, along with other really cool Halloween projects and contests.

Step 1: What You Need

Parts Needed:

Aduino
ProtoShield
Servo
Wire
Pumpkin - Real, plastic or foam
12Volt battery
Car horn - $7 at local car shop or junkyard
Buttons and/or switches
LEDs - Any color, but I like orange
Heat shrink tubing

Tools you need:

Soldering Iron
Pliers
Pumpkin cutting/carving supplies
Glue gun

Step 2: Cut/Carve Up the Pumpkin

The foam pumpkins are really easy to carve. It looks like a classic, smiling, jack-o-lantern. The kids will never suspect anything.

You can use a real pumpkin, but I picked this one up for $5 at a local craft store. Using a real one is fine, but photographing it over a few days can get messy so I decided to use a foam version.

Step 3: Selecting a Nose Button

I had an arcade game button lying around, so I used it for the nose. Also, I had an old doorbell button I used to trigger the horn. You can use almost any button that you have in your scrap bin.

Step 4: Soldering the Nose Button

Solder some wires to the "nose button" so you can assemble the electronics outside the pumpkin. Attach one wire to the ground of the Arduino and the other wire to pin (7) (see schematic). Also, you need an additional wire with a 10K resistor to ground. Speaking of Halloween, that is some scary soldering! Yuck.

Step 5: Prep the LEDs to the Eyes

I added a couple of LEDs to the pumpkin's eyes. First, solder some extra wire to the LEDs so you can reach the Arduino once they are glued in place. A little heat shrink makes it look nice, and avoids short circuits. (Don't forget to add a 220 Ohm resistor in-between...see diagram in next step)

Step 6: Test the LEDs

Plug the positive (long lead) of one LED into pin 10 and the other into pin 11. Don't forget to add a 220 Ohm resistor in-between. The other lead (-) goes to the ground of the Arduino. I am using a ProtoShield, so there are plenty of ground pins. If you want, go ahead and upload the code (see later step) and test the LEDs.

Step 7: Add the LEDs to the Pumpkin

Now you can glue them to the inside of the pumpkin. I used hot glue and just held them in place until it cooled. Simple!

Step 8: Adding the Truck Horn

I had a 12V rechargeable battery that I pulled from a home alarm system. It didn't work for the alarm any more, but it will hold enough of a charge to blast the horn a few hundred times.

The positive (+) terminal from the battery connects to one terminal of the button. The other terminal of the button connects directly to the horn. The negative (-) terminal of the battery connects directly to the horn. (again, see schematic, it's easy!) Press the button for a sample blast!

Attention Electronics people:

Yes, I know I could have uses a TIP120 and a relay to trigger the horn! But this project is meant to be easy, and easily configured based on what parts are available. I had a servo and an old doorbell button, so that's what I used. (OK, I have a TIP120 and a relay too, but some people might not!)

Note:

Want to make a simple project? Just add a few Throwies for the eyes! Done!

Step 9: Attach the Servo to the Button

I had this servo from an old remote control car. Now it's going to be used to push the button that blasts the horn. The servo has 3 wires. The red goes to (+) the black to (-) and the white goes to pin (9). Cut the servo horn so it only has 1 "arm". This arm will end up pressing the button. Yes, I know there are a lot of easy ways to do this with electronics, but remember this is mostly junk, and anyone can easy see how this works. Besides, I kind of like the idea of using a servo to press a button...it seems so silly.

Picture 2 - I used a scrap piece of wood to mount the button and servo. Drill a hole about the size of the button.

Picture 3 - Attach the servo to the board so it can turn and press the button. (upload the code and test it out a few times. If necessary, remove the servo horn and adjust until it works)

Step 10: Add Another LED

When the button is pressed, I wanted an additional LED to light up the inside of the pumpkin. You can use any color LED, mine is a 10mm White LED. Solder some extra wires to the LED, as you did in step #5. The (+) of the LED goes to pin (6) with a 220 Ohm resistor, and the (-) goes to ground.

Step 11: Program the Arduino

Upload this code to your Arduino:

/* MAKE Magazine
Ardumpkin or Pumpuino, your call?
By Marc de Vinck
*/

#include "<"Servo.h">" // REMOVE the "quote" symbols from this line code!! I had to add them so instructables does not strip them out.

Servo myservo; // create servo object to control a servo

int inputPin = 7; // choose the input pin (for a pushbutton)
int val1 = 0; // variable for keeping track of the button status
int val2 = 0; // variable used for PWM of LEDs
int ledrt = 10; //right eye led
int ledlt = 11; //left eye led
int ledmain = 6; //White LED in center of Pumpkin
int pos = 0; // variable to store the servo position

void setup() {

myservo.attach(9); // attaches the servo to pin 9 to the servo object
myservo.write(90); // tell servo to go to position "90" or "off" position

pinMode(ledrt, OUTPUT); // declare LED as output
pinMode(ledlt, OUTPUT); // declare LED as output
pinMode(ledmain, OUTPUT); // declare LED as output
pinMode(inputPin, INPUT); // declare pushbutton as input
}

void loop(){
val1 = digitalRead(inputPin); // read input value
if (val1 == HIGH) { // check if the input is HIGH
trick();
}
else {
treat();
}
}

void trick(){

digitalWrite(ledmain,HIGH); //turn on main LED
digitalWrite(ledrt,HIGH); //turn on right eye LED
digitalWrite(ledlt,HIGH); //turn on left eye LED

for(val2 = 0 ; val2 <= 255; val2+=2) // fade in (from min to max)
{
analogWrite(ledlt, val2); //write left led at power of "val"
analogWrite(ledrt, val2); //write right led at power of "val"
analogWrite(ledmain, val2); //write main led at power of "val"
delay(30); // waits for 30 milliseconds for dimming effect
}

myservo.write(90); //set servo to "off" position
delay(10);

myservo.write(45); //set servo to "on" position
delay(500); // stay "on for 1/2 second

myservo.write(90); //set servo back to "off" position

delay(200);

digitalWrite(ledmain, LOW); // turn main pumpkin LED off
digitalWrite(ledrt,LOW); // turn right LED off
digitalWrite(ledlt,LOW); // turn left LED off
}

void treat(){ // this fades the LEDs on/off until button press

for(val2 = 0 ; val2 <= 255; val2+=50) // fade in (from min to max)
{
analogWrite(ledrt, val2);
analogWrite(ledlt, val2);
delay(30); // waits for 30 milliseconds for dimming effect
}
for(val2 = 255; val2 >=0; val2-=50) // fade out (from max to min)
{
analogWrite(ledrt, val2); //write left led at power of "val"
analogWrite(ledlt, val2); //write right led at power of "val"
delay(30); // waits for 30 milliseconds for dimming effect
}
}

Step 12: Final Thoughts

The Arduino is programmed to pulse the eye LEDs until the victim, I mean trick-or-treater, presses the big red button. At that point the bright white LED will glow, there will be a slight delay, and the servo will trigger a blast from the horn. With any luck the trick-or-treater will drop their bag of candy and run....Mmmmm candy.

Looks like the kids are in for a shock at my house this year. I'll let you know what the neighbors think after the first few hundred blasts.

Note: Do not leave this pumpkin unattended. You don't want anyone getting too close, since the horn is really loud and could damage you hearing. Don't put your ear right up against the pumpkin, and you should be fine. However, you never know what a kid might do. Besides, you want to be there when they scream and drop their loot! Have fun, and watch out for any blinking pumpkins!

This build can be found on MAKE too!

Happy Halloween!