Instructables Electronics Project: Prank Box

Prank Box Assembly Time: 5-8 hours
Difficulty: Beginner
Designer: Instructables

The Prank Box is basically a sealed wooden box with an electric bell inside that is activated by a key switch. Once it is turned on, a relay inside the box is latched and it cannot be turned off without knowing the secret trick (spoiler alert: magnets). Quite understandably, a completely sealed box with a ringing bell inside that doesn't seem to stop can quickly become maddening. It is very funny to watch people ponder the implications of the device, reluctantly turn it on, and then stress out when they cannot turn it off. It is even funnier to get panicked emails from your friend in Canada after you mail it to him without any explanation, and he decides to ignore the directions on the box and turn it on.
Required tools and components:

Qty.
Description Mfr. P/N
1
9V Battery ALK 9V 522
4
D-Cell Battery ALK D EN-95
1
Heat Shrink Tubing FIT-221B-3/16-BK100
1
SPDT Reed Switch 35-756-BU
1
Pushbutton Switch A101-RD
1
Battery Snap SBS-IR-1-R
1
9V Battery Clip GBH-1009-R
100
Cable Ties KSS 0301CV-200 CLEAR-R
1
4-D Battery Holder BH-142-A-R
1
DPDT Relay AL-D9W-K
Parts
Wood glue & woodworking tools
Heat gun
Paintbrushes
Epoxy
Clamps
Electric bell
Drill and 1/8" drill bit
Red and black wire
Soldering iron

Step-by-Step Instructions

Step 1 - Review Parts and Download Templates

Take a moment to be sure you have all the required parts. You can download the two template files titled "DoNotBox.cdr" and "DoNotBox.eps" here

Step 2 - Insert Lock

Insert the lock into the hole in the front panel from front to back and then epoxy it firmly in place.

Insert Lock
Insert Lock

Step 3: Mark Mounting Holes for Components

Place the wooden mounting bracket atop the bottom side of the box and place all of the components atop their designated spots on the bracket. The reed switch does not have a designated spot, but it should line up flush with the edge of the bracket on the side nearest the 9V battery holder.

Mark Mounting Holes for Components
Mark Mounting Holes for Components
Mark Mounting Holes for Components

Step 4: Glue the Inner-Side of the Box Bottom

The bracket should be placed on top and line up to the edge of the box, so when the box is put together the reed switch is flush against the wall of the box. Clamp in place and wait for it to dry.

Place bracket on top and line up to the edge
Glue the Inner-Side of the Box Bottom
Glue them together
Start drilling holes

Step 5: Drill Mounting Holes

Drill the mounting holes with a 1/8" drill bit. It should go deep into the wood, but not pass all the way through.

Drill Mounting Holes
Drill Mounting Holes
Drill Mounting Holes

Step 6: Mount Components

Lay two zip ties vertically across the battery holder's footprint and another two horizontally and mount all of the major components to the bracket with screws.

Mount Components
Mount Components
Mount Components

Mount Components
Mount Components
Mount Components

Step 7: Wire It Up

Attach the red wire to the common connections for the reed switch and the key switch. Then attach another red wire to the normally open (NO) connections on both switches. Connect these two wires to the red wire from the 9V battery clip. Attach black wires to the two normally closed (NC) connections on both switches. Connect these two wires to the black wire from the 9V battery clip.

What you have just done is create a situation in which ground is always connected in the circuit. By engaging one of the switches, you are introducing a positive voltage. This flips the polarity one way or another and latches the relay open or closed. Now when you turn the key, it latches it closed and keeps the bell ringing. When you engage the reed switch, it flips the polarity and latches it open and turns off the bell.

You will need to wire the bell to the D battery holder and the relay. First, wire together the black wire from the battery holder to the frame of the bell. Then connect the red wire from the battery holder to the center pin on the relay. Last, connect the red wire from the battery holder to the coil connection on the bell. This is the mounting terminal not connected to the frame. Cover all the exposed electrical connections with shrink tubing.

Schematic and Diagram

Wire It Up
Wire It Up
Wire It Up

Wire It Up
Wire It Up
Wire It Up

Wire It Up
Wire It Up
Wire It Up

Wire It Up
Wire It Up
Wire It Up

Step 8: Heat Shrink Electrical Connections


Heat Shrink Electrical Connections
Heat Shrink Electrical Connections

Step 9: Insert Batteries

Insert D batteries in the battery holder and using four more zip ties, firmly band all of the batteries in place both vertically and horizontally.

Insert Batteries

Step 10: Glue Relay

Plug in the 9V battery and epoxy the battery holder in place. Hot glue the relay to the mounting bracket in the free space next to the battery.

Insert Batteries
Insert Batteries

Insert Batteries
Insert Batteries

Step 11: Bundle Everything Together with Zip Ties

If possible, zip tie this bundle to the battery pack to prevent it from interfering with the bell.

Bundle Everything Together with Zip Ties

Step 12: Glue it together

Test to make sure the bell turns on and off. Seal the box shut and apply wood glue to all of the joints and firmly clamp it together.

Glue it together
Glue it together
Glue it together

Glue it together
Glue it together
Glue it together

Step 13: Use a Belt Sander to Round the Edges


Round the Edges
Round the Edges

Step 14: Make a Sign

Laser cut the sign using the template from Step 2. If you don't have a laser cutter, you can use a service like Ponoko, or do this the old-fashioned way with saws, stencils and Exacto blades.

Make a Sign

Step 15: Sand and Stain (Optional)

Sand the box and wipe it clean. You can put on a coat of stain in a singular direction. When it has dried, lightly sand again and apply the stain in the opposite direction. Lightly sand once more and lay one last coat of stain in the initial direction.

Sand and Stain

Step 16: Affix the Sign


Affix the Sign

Step 17: Project Complete

It is simply good to distance yourself from the person who engages the box. Remember to be a good southern neighbor and eventually tell them how to turn it off. However, I think 20 - 30 minutes is about a fair amount of time to wait before telling them about the magnet triggered reed switch on the side of the box. Also, when triggering the reed switch, make sure the key is not inserted in the lock and turned. If it is, this will not work.

Project Complete
Prank Box