Talking Caps Lock Key Prank

Do you know someone that types with the Caps Lock on? How would you like to modify their keyboard so that it yells at them when they hit the Caps Lock key? In this project I am going to show you how to do just that. All you have to do is wire a small sound module to the circuit board inside the keyboard. You don't even need to solder anything.

Here are the tools and materials that you will need for this project.

Materials:
Keyboard
Sound Module
2 feet of thin insulated wire
Tape

Tools:
Wire Strippers
Sharp Knife
Multimeter

The first thing that you need to do is select a sound module that will play a sound when the Caps Lock key is pressed. You can use the sound module from a toy or a musical greeting card. I decided to use a record/play back module that lets you record your own sound clip.

Each sound module is wired together differently. On my sound module, one side of the play switch is connected to ground and the other side of the play switch is connected to the microchip on the board. If your sound module is wired together differently, then you may need to modify the procedure slightly. 

Next you need to open up the housing of the keyboard. In most cases, you can simply unscrew the back of the keyboard.

Inside a keyboard, there is a small circuit board that processes the signals from all the key sensors. This circuit board is connected to the USB cable with several wires. We need to connect to the negative power line (ground). This is usually colored black. Occasionally there are two black wires. These will be connected together. So either one can work.

Take a one foot long section of your wire and strip the insulation off of the ends. Then connect one end to one of the negative input wires on the keyboard. In my case, I was able to just insert the wire into the pin connector on the board.

The easiest way to connect the keyboard to the sound module is to connect the negative terminals of each circuit together so that they share a common ground. To do this, I took the wire that we just connected to the negative terminal of the keyboard and I connected the other end to the negative terminal of the sound module's battery. Since the sound module uses a 9 volt battery, I just inserted the wire through the teeth of the negative terminal and attached the battery connector. This was enough to hold the wire tightly in place.

In order to be able to activate the play function on the sound module we need to connect a wire to the play switch.

Start by locating the play switch. Then determine which side of the switch is connected to the negative terminal (ground) and which side of the switch is connected to the processor chip. 

Take a second piece of wire and strip the insulation off the ends. Then connect one end of the wire to the side of the switch that is wired to the chip on the sound module (not the side that is connected the negative terminal).

Fortunately there was an open pin hole on the board that was connected to the appropriate side of the switch. To connect to it, I just inserted the wire through the hole and then twisted the wire against itself so that it made a tight connection with the board. I didn't even need to solder it.

The LEDs on a keyboard are wired so that one end is connected to the positive terminal on the circuit board and the other end is connected to the integrated circuit. When the LED is turned on, the integrated circuit uses a transistor to connect that end of the LED to the negative terminal. This completes the circuit and the LED lights up. 

We want to connect the wire from the play switch on the sound module to one of the terminals on the LED or its resistor. The best place to connect the wire is the terminal on the LED or the resistor that is closest to the integrated circuit. This terminal will have the lowest voltage when he LED is activated. By connecting the play switch to this low voltage, it will simulate the play switch being pressed and activate the sound module. 

Turn on the Caps Lock function so that the LED is on. Then take the free end of the wire that is attached to the play switch and touch it to the terminals on the LED and the resistor. At least one of the terminals will activate the play function on the sound module. On my keyboard, touching the wire to either terminal of the resistor activated the play function.

I connected the wire at this point by looping it around the lead of the resistor and then twisting it so that it was tight and made a good connection. Then I wrapped the end of the wire in tape to prevent any unwanted shorts. 

Most keyboards don't have enough room inside of them to fit a sound module and its battery. So I ran the wires outside of the keyboard so that the sound module could fit underneath the keyboard. If there  are no gaps in the housing of the keyboard, then you will need to cut a small slot for the wires. After running the wires, reassemble the housing. 

To keep the sound module hidden, I taped all the parts to the bottom of the keyboard. Be careful to make sure that none of the parts stick out past the feet of the keyboard. Otherwise the keyboard will not sit flat on the table and the joke will be ruined.

The last thing that you need to do is record a sound clip that you want to play when Caps Lock button is pressed. I decided to use a clip of Billy Mayes saying his tag line "Hi Billy Mayes here!" I thought that this was appropriate since Billy Mayes always spoke with the kind energy and enthusiasm that you might associate with typing in all caps.