5.1 Reading Button Value

In this interactive project, we’ll venture into the realm of button controls and LED manipulation.

The concept is straightforward yet effective. We’ll be reading the state of a button. When the button is pressed down, it registers a high voltage level, or ‘high state’. This action will then trigger an LED to light up.

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	-
Breadboard	BUY
Jumper Wires	BUY
Resistor	BUY
LED	BUY
Button	BUY

Available Pins

• Available Pins

  Here is a list of available pins on the ESP32 board for this project.

  For Input	IO14, IO25, I35, I34, I39, I36, IO18, IO19, IO21, IO22, IO23
  For Output	IO13, IO12, IO14, IO27, IO26, IO25, IO33, IO32, IO15, IO2, IO0, IO4, IO5, IO18, IO19, IO21, IO22, IO23

• Conditional Usage Pins (Input)

  The following pins have built-in pull-up or pull-down resistors, so external resistors are not required when using them as input pins:

  Conditional Usage Pins	Description
  IO13, IO15, IO2, IO4	Pulling up with a 47K resistor defaults the value to high.
  IO27, IO26, IO33	Pulling up with a 4.7K resistor defaults the value to high.
  IO32	Pulling down with a 1K resistor defaults the value to low.

• Strapping Pins (Input)

  Strapping pins are a special set of pins that are used to determine specific boot modes during device startup (i.e., power-on reset).

  Strapping Pins

  IO5, IO0, IO2, IO12, IO15

  Generally, it is not recommended to use them as input pins. If you wish to use these pins, consider the potential impact on the booting process. For more details, please refer to the Strapping Pins section.

Schematic

To ensure proper functionality, connect one side of the button pin to 3.3V and the other side to IO14. When the button is pressed, IO14 will be set to high, causing the LED to light up. When the button is released, IO14 will return to its suspended state, which may be either high or low. To ensure a stable low level when the button is not pressed, IO14 should be connected to GND through a 10K pull-down resistor.

Wiring

Note

A four-pin button is designed in an H shape. When the button is not pressed, the left and right pins are disconnected, and current cannot flow between them. However, when the button is pressed, the left and right pins are connected, creating a pathway for current to flow.

Code

Note

• You can open the file 5.1_button.ino under the path of esp32-starter-kit-main\c\codes\5.1_button.

• After selecting the board (ESP32 Dev Module) and the appropriate port, click the Upload button.

• Always displaying “Unknown COMxx”?

Once the code is uploaded successfully, the LED lights up when you press the button and goes off when you release it.

At the same time you can open the Serial Monitor in the upper right corner to observe the value of the button, when the button is pressed, “1” will be printed, otherwise “0” will be printed.

How it works

The previous projects all involved outputting signals, either in the form of digital or PWM signals.

This project involves receiving input signals from external component to the ESP32 board. You can view the input signal through the Serial Monitor in Arduino IDE.

1. In the setup() function, the button pin is initialized as an input and the LED pin is initialized as an output. The Serial communication is also initiated with a baud rate of 115200.

   void setup() {
       Serial.begin(115200);
       // initialize the button pin as an input
       pinMode(buttonPin, INPUT);
       // initialize the LED pin as an output
       pinMode(ledPin, OUTPUT);
   }
   

   • Serial.begin(speed): Sets the data rate in bits per second (baud) for serial data transmission.

     • speed: in bits per second (baud). Allowed data types: long.

2. In the loop() function, the state of the button is read and stored in the variable buttonState. The value of buttonState is printed to the Serial Monitor using Serial.println().

   void loop() {
       // read the state of the button value
       buttonState = digitalRead(buttonPin);
       Serial.println(buttonState);
       delay(100);
       // if the button is pressed, the buttonState is HIGH
       if (buttonState == HIGH) {
           // turn LED on
           digitalWrite(ledPin, HIGH);
   
       } else {
           // turn LED off
           digitalWrite(ledPin, LOW);
       }
   }
   

   If the button is pressed and the buttonState is HIGH, the LED is turned on by setting the ledPin to HIGH. Else, turn the LED off.

   • int digitalRead(uint8_t pin);: To read the state of a given pin configured as INPUT, the function digitalRead is used. This function will return the logical state of the selected pin as HIGH or LOW.

     • pin select GPIO

   • Serial.println(): Prints data to the serial port as human-readable ASCII text followed by a carriage return character (ASCII 13, or ‘r’) and a newline character (ASCII 10, or ‘n’).