6.1 Fruit Piano¶

Have you ever wanted to play the piano but couldn’t afford one? Or maybe you just want to have some fun with diy a fruit piano? Well, this project is for you!

With just a few touch sensors on the ESP32 board, you can now play your favorite tunes and enjoy the experience of playing the piano without breaking the bank.

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
ESP32 Starter Kit	320+	ESP32 Starter Kit

You can also buy them separately from the links below.

COMPONENT INTRODUCTION	PURCHASE LINK
ESP32 WROOM 32E	BUY
ESP32 Camera Extension	-
Jumper Wires	BUY
Resistor	BUY
Buzzer	BUY
Transistor	BUY

About the Touch Pins

The ESP32 microcontroller has built-in touch sensor functionality, which allows you to use certain pins on the board as touch-sensitive inputs. The touch sensor works by measuring changes in capacitance on the touch pins, which are caused by the electrical properties of the human body.

Here are some key features of the touch sensor on the ESP32:

Number of touch pins
The ESP32 has up to 10 touch pins, depending on the specific board. The touch pins are typically labeled with a “T” followed by a number.
- GPIO4: TOUCH0
- GPIO0：TOUCH1
- GPIO2: TOUCH2
- GPIO15: TOUCH3
- GPIO13: TOUCH4
- GPIO12: TOUCH5
- GPIO14: TOUCH6
- GPIO27: TOUCH7
- GPIO33: TOUCH8
- GPIO32: TOUCH9
Note

The GPIO0 and GPIO2 pins are used for bootstrapping and flashing firmware to the ESP32, respectively. These pins are also connected to the onboard LED and button. Therefore, it is generally not recommended to use these pins for other purposes, as it could interfere with the normal operation of the board.
Sensitivity

The touch sensor on the ESP32 is very sensitive and can detect even small changes in capacitance. The sensitivity can be adjusted using software settings.
ESD Protection

The touch pins on the ESP32 have built-in ESD (Electrostatic Discharge) protection, which helps to prevent damage to the board from static electricity.
Multitouch

The touch sensor on the ESP32 supports multitouch, which means that you can detect multiple touch events simultaneously.

Schematic

../../_images/circuit_6.1_fruit_piano.png

The idea behind this project is to use touch sensors to detect when a user touches a specific pin. Each touch pin is associated with a specific note, and when the user touches a pin, the corresponding note is played on the passive buzzer. The result is a simple and affordable way to enjoy the experience of playing the piano.

Wiring

In this project, you need to remove the ESP32 WROOM 32E from the expansion board and then insert it into the breadboard. This is because some pins on the expansion board are connected to resistors, which will affect the capacitance of the pins.

Code

Note

You can open the file 6.1_fruit_piano.ino under the path of esp32-starter-kit-main\c\codes\6.1_fruit_piano directly.
Or copy this code into Arduino IDE.

You can connect fruits to these ESP32 pins: 4, 15, 13, 12, 14, 27, 33, 32.

When the script runs, touching these fruits will play the notes C, D, E, F, G, A, B and C5.

How it works?

touchRead(uint8_t pin);
This function gets the touch sensor data. Each touch sensor has a counter to count the number of charge/discharge cycles. When the pad is touched, the value in the counter will change because of the larger equivalent capacitance. The change of the data determines if the pad has been touched or not.
- pin GPIO pin to read TOUCH value
This function returns a value between 0 and 4095, with a lower value indicating a stronger touch input.

Note

threshold needs to be adjusted based on the conductivity of different fruits.

You can run the script first to see the values printed by the shell.

After touching the fruits on pins 12, 14, and 27, the printed values are as follows. Therefore, I set the threshold to 30, which means that when a value less than 30 is detected, it is considered to be touched, and the buzzer will emit different notes.