This Dot Matrix Board is made up of three MAX7219 that could show any letter or number consecutively. This Arduino project is based on this website. From the previous website, I added 2 more Dot Matrix, one button, and one speaker. While the letters or numbers are showing, by pressing the button and holding it, the speaker could create a sound to drag people's attention. The whole project is made and contained in a box, making it convenient to carry around.

Step 1: Prepare Materials

3 8x8 Dot Matrix (MAX7219)
1 Bread Board
1 Arduino Leonardo
Jump Wires
Cardboard (Size may differ)
Utility knife
1 Blue Resistor
1 Button
1 Speaker
Tape
Glue

Step 2: Cut the Outer Layer

1. Cut a 10cm x 3.3cm rectangle in the middle of the cardboard

2. Cut a circle with a radius of 1.5cm beside the rectangle, leaving 2.5cm in between

(The first picture is the shape you should aim, its usage will be to put the Dot Matrix and the button inside, but do not put them inside in this step)

3. Cut two 24.5cm x 10cm pieces (Second picture)

4. Cut two 13cm x 10cm pieces (Second Picture)

5. Choose one of the 13cm x 10cm piece and cut a 6.5cm x 2cm hole to let the wires get out (Third picture)

Step 3: Connect the Dot Matrix (MAX7219)

Prepare 3 Dot Matrix in this step. There are two sides for each Dot Matrix: a side with green and a side without the green. When connecting the Dot Matrix together, the Dot Matrix should be connected with different sides, as shown in the picture; Meaning one with it will have wires connected on the side without green, and the other one with have wires connected on the side with green. The VCC should be connected to VCC, GND should be connected to GND, DIN should be connected to DIN, and so on. Repeat these until you have three Dot Matrix connected to each other.

Step 4: Connect the Dot Matrix to the Circuit Board

Use 5 jump wires that could connect the Dot Matrix and the Bread Board. Choose the Dot Matrix on the right to be the one that connects to the Bread Board. When the five wires are connected on the Bread Board, let:

VCC connect to the positive horizontal part
GND connect to the GND part of the Arduino
DIN connect to Digital Pin 11
CS connect to Digital Pin 10
CLK connect to Digital Pin 13

Step 5: Button

Connect the positive and negative of the button onto the Bread Board. Use the blue resistor to connect the negative of the button to the negative horizontal on the Bread Board, and use a wire and connect the negative horizontal to GND on the Arduino. Connect the positive of the button to the positive horizontal, and use another wire to connect the positive horizontal to 5V on the Arduino. At last, from the negative of the button, use a wire and connect it to Digital Pin 2 on the Arduino.

Step 6: Speaker & Others

Connect the positive of the speaker to Digital Pin 6 on the Arduino, and negative of the speaker to GND. Also, use a wire to connect Digital Pin 0 to the positive horizontal on the Bread Board.

Step 7: Combine

After connecting the wires and making the outer layer, the last step is to make the box. On the first cardboard (with a rectangle and a small circle), place the three Dot Matrix and the button (Picture 1). Make sure the Dot Matrix follows the correct sequence and the same direction. Glue the two largest cardboard pieces (24.5cm x 10cm) on the length of the first cardboard piece, then glue the smaller cardboard pieces on the width (13cm x 10cm). At last, stick the speaker right above the hole made in the smaller cardboard piece.