Hello, in this tutorial I wanted to take advantage of the only piece of cardboard that I had in my whole house, because of the quarantine I couldn't get more, but I don't need it! With a small piece we can do interesting experiments.
This time I bring you a Velocity Sensitive Cardboard Keyboard that works with proximity IR sensors. Depending on whether we play a piano key faster or slower, the musical note will sound more or less hard, respectively.

Step 1: Materials

For Hardware

Cardboard sheet, only 55 cm x 25 cm needed
Scissors or scalpel
Hot silicone gun
Gray, white, black paint (optional)
Brush (optional)
Aluminum rod 5 mm in diameter and 16.3 cm long
Instructables sticker (optional)
Pencil, pen or sharpie
Ruler
Rubber strips or some elastic material
Sewing machine
Tweezers

For Circuit

Arduino, I used Arduino Mega 2560
5 10k Ohm resistors
1 1k Ohm resistor
1 100 Ohm resistor
Cable
1 buzzer
5 reflective IR sensors, I used QRE1113
Universal pcb
Battery (optional)
Soldering iron
Tin
Caiman-caiman cable

Step 2: Cut Cardboard Pieces

Cut all the cardboard pieces with the dimensions shown in the image, I did it using a ruler and scalpel because I did not have access to a laser cutter, however, I also attached the vector file so that you can easily cut it by laser machine.

Step 3: Make the 5 Piano Keys

Join the pieces of each piano key using hot silicone, as shown in the images. Repeat the process 5 times.

Step 4: Make the Piano Base

Join the pieces of the piano base using hot silicone, as shown in the pictures. The base is made up of the drawer and the cover.

Step 5: Paint Everything With Your Favorite Colors

I decided to paint the piano keys white, as they traditionally are, and the piano base gray to perfectly match the Instructables logo.

Step 6: Locate the Rubber Straps

The rubber strips allow the piano keys to return to their original position, locate them as I show in the images.

Step 7: Paste the Sticker (decorate)

At the end of this stage, you should come up with 3 main parts, the cover, the base and the keys of your piano.

Step 8: Construction of the Circuit

The circuit is designed with Arduino, you can build it as you see fit, the following steps are tips describing the way I did it.

Untitled Sketch 4.fzz
Download

Step 9: Cut Universal PCB and Solder

The sensors that I used are SMD, therefore I need a PCB to solder them on, cut 2 x 3 hole rectangles from universal PCB. And add tin to the 4 holes at the ends to be able to solder the IR sensor (see images).

Step 10: Solder Cables and Resistors

To avoid further complications, I decided to solder the resistors directly to each other so that I could insert them all into the Arduino. Finally, I soldered all the cables guiding me with the fritzing design.

Remember to check your circuit connections with a multimeter.