The Mystery Beeping Prank is a device hidden in a hollowed out book that beeps intermittently at different frequencies. I made this because I am surrounded by a lot of incredibly creative people who have a penchant for pranking one another, and this seemed like the most subtly annoying thing that I could think of. In fact, I imagine this will be outright maddening for all those not in on the joke. Hopefully these people will have a good sense of humor about it, and not be too permanently scarred by the experience. It is all in good fun, after all.

Step 1: Go Get Stuff

You will need:

(x1) Arduino micro (Radioshack #276-258)
(x1) 40 pin socket (Radioshack #276-1996)
(x1) LM386 audio amp (Radioshack #276-1731)
(x1) 220uF capacitor (Radioshack #272-1029)
(x1) speaker (Radioshack #273-092)
(x1) Prototype circuit board (Radioshack #276-150)
(x2) AA x 4 battery holders (Radioshack #270-391)
(x1) Book
(x1) Rubber cement
(x2) 12" x 9" x 1/4" wood blocks

Step 2: Socket

Solder the socket onto the circuit board.

Make sure to leave room for the LM386 chip.

Note: The schematic shown here applies to the next 7 steps.

Step 3: LM386

Solder the LM386 chip onto the circuit board next to the socket.

Step 4: Capacitor

Solder the positive lead of the capacitor to pine 5 on the LM386 chip.

Solder the negative lead to any free terminal.

Step 5: Wiring

Wire the Arduino micro's ground pin to ground, and the VI (voltage in) pin to the 12V rail.

Solder pin 6 from the Arduino micro to pin 2 on the LM 386 chip.

Connect pins 3 and 4 on the LM386 to ground, and pin 6 to power.

Note: I made some of these connections with solder below the board.

Step 6: Battery Packs

Connect the battery packs in series on the circuit board.

Connect the single red wire to the 12v power rail, and the lone black wire to the ground rail.

Step 7: Speaker

Solder the red wire coming off of the speaker to the negative lead of the 220uF capacitor, and the black wire to ground.

Step 8: Program

Program the Arduino with the following code:

/*
  Mystery Beeping Prank
  by Randy Sarafan
  
  For more information please visit:
  https://www.instructables.com/id/Mystery-Beeping-Prank/
  
  Based upon:
  Multiple tone player
  created 8 March 2010
  by Tom Igoe 
  (based on a snippet from Greg Borenstein)

  This example code is in the public domain. Do what you may.

 */

//establish variables
int randomTone;
int randomTime;



void setup() {

  //set the initial instance to 5 seconds
  randomTime = 5;
  
}


void loop() {
  
  //randomTime is the number of seconds to wait
  for(i = 0, i < randomTime, i++){    
      delay(1000);
  }
  
  //select a random tone in audible range
  randomTone = random(100, 10000);

  // play a tone on pin 6 for 200 ms
  tone(6, randomTone, 200);
  delay(200);

  // turn off tone function for pin 6
  noTone(6);

  //pick a number of seconds to wait for next tone
  //Between 15 minutes and an hour
  randomTime(900, 5400);

}

Step 9: Insert

Insert the Arduino micro into the socket such that the pins on the Arduino line up with the wiring connections that have already been made.

Step 10: Clamp

Figure out the depth that you intend to hallow out of the book, and clamp that thickness of pages between two sheets of wood.

Step 11: Mark and Drill

Make marks in each of the corners of the inner square frame that you intend to hallow.

Drill them with a 1/8" drill bit.

Step 12: Cut

Use these holes to cut out the inner square frame.

Note: I started by using a handsaw, got frustrated, and quickly progressed to using a power tool (not pictured).

Step 13: Glue

Line the inside edge of the cut square with two to three layers of rubber cement.

Step 14: Unclamp

Remove the clamps from the wood and admire you handywork in succesfully hollowing out a book.

Step 15: Trim (optional)

If necessary trim away the ICSP pins so that the circuit can fit flatly inside the book.

Step 16: Power

Insert the batteries to power up the circuit.

Step 17: Stash

Stash away your circuit inside of your hollowed out book, and close the cover.

Step 18: Put It on a Shelf

When you are done, put the book away on the bookshelf and admire your handiwork as people wonder where the heck that beep is coming from.

For added ammusement, insist that you are not hearing any beeps.

Introduction: Mystery Beeping Prank