This project is based off of an idea formed by Mark Rober and I Like to Make Stuff.

There are very limited ways to communicate with other drivers on the road. Most people will hear a car horn and get the idea that the person using this horn is most likely upset. This project allows for a multitude of sounds to be played through a speaker placed within your car, providing effective communication on the road. To add to this, you can play anything from musical horns to animal sounds from your car as you can use any sound file you can get your hands on.

Throughout this process, you will create a circuit that will receive power, change the voltage of this power output, amplify a set of custom audio effects, and output these effects to a mounted speaker.

Supplies

Adafruit Audio FX sound board
Amplifier
DC voltage converter (12v to 5v)
Push buttons
Indoor / outdoor speaker
Fuse (12v)
Fuse wire tap (optional)
Wire
Cable screws
Cable connector plugs
Solder & Soldering iron
Hot glue & hot glue gun
3D printer (optional)

Step 1: Planning

To start this project I created a basic plan for how the dynamics of the components will piece together to produce the desired outcome.

How it works:
The car battery is wired to a fuse that runs to a connector, this is then wired to the power input for the amplifier and DC converter. The DC converter changes the voltage from 12V to 5V, therefore powering the sound FX board. Once this board receives an input through pressing one of the various buttons, it will output a programmed sound to the amplifier. The amplifier will then output audio to the speaker.

Step 2: Making the Case

The next step is to design an enclosure to place all the smaller components in that will protect them and make the project look clean.

I designed a box using Fusion 360 that has slots for all the necessary parts. 3D printing is an easy and cost effective solution to this step. The added bonus of 3D printing the case is that it is highly modifiable, this allows you to alter the design if your components are slightly different or if you want to place the case somewhere that will not fit the design I used. I specifically made my box the same size as the empty radio slot in my car.

Note: You do not need to use a 3D printer to create the box, you can use any material that is sturdy enough to support the project and can withstand being in a heavily used environment.

Step 3: Wiring

After designing the case to place the project in, you will need to wire it all together.

The way I did this was by using connectors that connect to the speaker and battery, this allows the box to be easily removed without the need to cut or unsolder any wires. I used wire screws to neatly connect multiple wires at once to avoid the need to solder these wires together. I connected all the ground wires from the battery and all the positive wires from the battery. I also used a number of wire screws to connect all the ground wires from the buttons that lead to the sound FX board. As I needed to be able to easily remove the sound FX board from the project, I soldered all the wires that connect to it to a set of pin connectors, these can easily slot on and off of the board at will.

Note: This should be done before placing the components into the case however I did not have any photos of wiring before I had put the two together.

You will also need to wire up the connectors that run from the box to the wires that will later be placed inside the dash of the car. These are made by connecting the alternate plugs and some electrical terminals.

Step 4: Assembly

To finish the box, the wired project must be test fit, and placed into the case.

For this step I placed the buttons in their slots, hot glued them into place, and test fit the rest of the project. I also used hot glue to hold a few other components in place such as the wire screws.

Step 5: Programming the Audio

The next step is to program sound files on the sound FX board.

To do this, I downloaded a variety of sound files that I wanted to use for the design and converted them to .wav files with an online file converter. I then connected the board to my computer to transfer the desired files onto the board. There are a variety of ways these files can be programmed by changing the names of each file.

Note: Here is a link with information on how to program the board.

Step 6: Placing Design in Car (Part 1 - Engine Bay)

The bulk of the design is now complete. All that is left to do is to connect a fuse to the positive side of the car battery (or use a wire tap in the car's fuse box), install the speaker into the car, and wire both the battery and speaker inside the car, to the project.

I screwed the speaker in under the front bumper of my car as to protect it from environmental damage and fed wires up into the engine bay. I also used a wire tap to connect the design to a positive power source (I used a wire tap as if I were to connect it directly to the battery, the design could drain the car's power when not in use). I have also removed the old, unused radio from the dash of my car so there is a place to slot the design into.

To run the wires into the dash I fed them along the top of the engine bay towards a rubber grommet (I used where the wires for the steering are fed through for this) and pushed a metal straw through to feed the wires into. I then removed the straw to have the grommet close the hole and keep it as water tight as possible.

Step 7: Placing Design in Car (Part 2 - Inside the Car)

To finish the project, you will need to run the power and speaker wires from the engine bay into the cabin of the car and solder the connectors onto the end of the wires. From here you can connect the project to the speaker / power and begin using your new custom car horn.

I first soldered on some electrical terminal plugs onto the ends of the wires that were fed through from the engine bay to connect to the speaker wires inside the box, the cord that I had wired up before will then connect to both the box and the newly soldered wires.

The next step is to run the other cable that had been previously soldered to power. To do this, I ran the positive side of this cable to a power source (originally I stated that you can use the car battery however I changed my method to drawing power from the fuse box inside the dash of the car; both will work) and the negative side to a section of unpainted metal. This was done by wrapping the negative wire around a self tapping screw and drilling it into the metal under the steering wheel.

Finally, you will need to connect all the plugs and slide the box into your radio slot to begin using your new horn.

Step 8: Additional Notes

Due to the design of the case and wiring, the project can be easily removed and altered.

A few things that you may want to adjust accordingly are:
The volume level of the speaker (there should be a dial on your amp)
The audio effects on the sound FX board (the pin connectors allow this to be removed at will)