Keyestudio ESP32 Manual page 144

ESP32 Starter Kit
7. Code Explanation
float checkdistance() :Self-defining function. It greatly reduces loop() by collecting some specific codes which can be
directly recalled.
delayMicroseconds(); Delay function. delay()is in ms while delayMicroseconds() is in um for some precise delays.
pulseIn(pin, value) :Pulse-grabbing function. pin: the number of the Arduino pin on which you want to read the pulse.
Allowed data types: int. value: type of pulse to read: either HIGH or LOW. Allowed data types: int.
Please refer to the website for more details[pulseIn() - Arduino Reference]:
8.5.27 Project 26: Human Body Piano
1. Description
The analog piano includes a development board and an ultrasonic sensor. It enables to play different tones by detecting
the position of your fingers. Thus, this module is able to stimulate a piano to perform music and songs.
140 Chapter 8. Arduino Tutorial