ESP32 Starter Kit
(continued from previous page)
if (digitalRead(button) == LOW) { //judge whether the button value is 0
ledState = !ledState; //ledStart is equal to the inverse of its␣
˓→original value, which can be used to light the LED on and off
digitalWrite(led, ledState);
}
while (digitalRead(button) == LOW); //hold the button for the while loop, exit␣
˓→it when release it
}
}
7. Code Explanation
pinMode(button, INPUT); Set pin IO15 on the development board to input, so that the state of button can be identified.
When we press the button, IO15 is at a low level(0). If we release it, IO15 will be at high(1).
value = digitalRead(button); digitalRead(button) reads the high and low level (1 or 0) of the digital IO15 pin and
assigns the button value to value.
Serial.begin(9600); Set the serial baud rate. It is necessary to print value on serial port.
Serial.print(“Key status:”); Serial port prints value. Contents in print() will be printed. If it is character string,
quotation marks are needed, for instance, “Key status:”.
Serial.println(button); Serial port prints contents in println() in a new line. Here we print the button value.
if (digitalRead(button) == LOW) { . . . }: Determine if the button pin is equal to the low level. If so, execute the if
statement {. . . }, otherwise not executed.
! takes the inverse operator, so if this value is 1, it’s 0, and if it’s 0, it’s 1, so we can turn a light on and off by pressing
a button.
== is used to determine whether the value of the variable on the left is equal to the value on the right. Please refer to
the official website for details: https://www.arduino.cc/reference/en/.
92 Chapter 8. Arduino Tutorial
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