A beloved coworker is returning from Canada soon and in his honor I have created the car horn prank box. Basically, when the red button is pressed, and an LED blinks indicating that there is thirty seconds in which to hide the box somewhere dark. Once the thirty seconds expire, the next time that the box sense light, the car horn honks very loudly. Some fun places to hide the car horn is includes drawers, underneath jackets, in closets, buried in a backpack, or simple left in a room in which the lights have been turned off. The amount of potential mischief that this device can produce makes it a perfect welcome back gift.
Step 1: Materials
(x1) Car horn
(x1) Enercell 12V/5Ah Sealed Lead-Acid battery (Radioshack #23-945)
(x1) Arduino Uno (Radioshack #276-128)
(x1) LED holder w/LED (Radioshack #276-068)
(x1) LED holder (Radioshack #276-080)
(x1) 7805 voltage regulator (Radioshack #276-1770)
(x1) TIP31 NPN transistor (Radioshack #276-2017)
(x2) 10K ohm resistor (Radioshack #271-1335)
(x1) 1K ohm resistor (Radioshack #271-1321)
(x1) 220 ohm resistor (Radioshack #271-1313)
(x1) 10uF capacitor (Radioshack #272-1025)
(x1) 1uF capacitor (Radioshack #55047773)
(x1) 1N4004 diode (Radioshack #276-1103)
(x1) Small photocell (Radioshack #276-1657)
(x1) Red pushbutton switch (Radioshack #275-646)
(x1) Aluminum heatsink (Radioshack #276-1368)
(x1) Thermal compound(Radioshack #28-1098)
(x1) 12V automotive relay (Radioshack #275-001)
(x1) Dual PC Board (Radioshack #276-159)
(x2) Pack red and blue quick connects (Radioshack #64-3088)
Step 2: Mark and Drill
Drill through this mark with a 1/4" drill bit.
Step 3: Insert
Clean the epoxy of the photocell leads if necessary.
Let the assembly dry.
Step 4: Attach
Step 5: Drill
Step 6: Insert
In the adjacent 1/4" hole, install the red LED (in holder).
Finally, next to this install the photocell assembly.
Step 7: Break
Step 8: Heat Sink
Clean away any excess thermal paste from the sides of the voltage regulator.
Step 9: Cut and Glue
Glue the plywood shapes together to form an L-assembly.
Step 10: Attach the Arduino
Step 11: Start the Circuit
Step 12: Twist and Attach
Using a wire nut, twist this together with the ends of three of the red wires with quick connects attached.
Solder the wire without the quick connect attached to the voltage input pin of the 7805 regulator.
Step 13: Twist and Attach Again
Using a wire nut, twist this together with two of the black quick connect wires.
Solder the other end of the 6" black wire to ground on the circuit board.
Step 14: Transistor
Connect the emitter to ground on the circuit board (the rightmost pin).
Take a black wire with the quick connect attached, and solder it to the transistor's collector (the center pin).
Step 15: Wires
Attach a 6" red wire to the LED's anode (longer lead) and a 6" green wire to the cathode (the other shorter lead).
Attach a 6" red wire to one of the leads on the photocell and a 6" green wire to the other lead.
Step 16: Insulate
Step 17: Diode
Step 18: Attach the Circuit Board
Additionally, solder a 6" red wire to +5V power on the voltage regulator, and 6" black wire to ground.
Extend the output for the photocell, LED, pushbutton switch, and transistor base with 6" green wires.
Step 19: Mount the Relay
Step 20: Mount the Circuit Board
Step 21: Plug In
Connect the black wire to one of the ground pins on the Arduino.
Attach the wire from the photocell to pin A0.
Attach the wire from the 1K resistor (connected to the base of the transistor) to pin D2.
Attach the wire from the LED wire to pin D3.
Attach the wire from the pushbutton switch to pin D4.
Step 22: Connect the Relay
Connect the black wire from the TIP31 collector pin to the anode side of the relay coil.
Connect a 12V quick connect wire to one of the sides of the relay switch.
Connect a black quick connect wire (that is not connected to ground) to the other side of the relay switch.
Step 23: Another Connector
Step 24: Program
Step 25: Insert
Step 26: Battery
Connect a black wire from the circuit board's ground to the ground terminal on the battery.
Connect a red wire from the circuit board's 12V connection to the power terminal on the battery.
The circuit is now activated.
Step 27: Horn
Connect the remaining black wire from the relay to one terminal on the horn and a black ground wire from the circuit board to the other terminal on the horn.
Step 28: Connect
Step 29: Close
Step 30: To Use
The LED will flash on and off for 30 seconds. During this time, you should hide the prank box somewhere very dark.
After 30 seconds, the next time the prank box sense light, it will honk.