ESP32 - Serial Input/Output

Video Tutorial

you can watch this video tutorial

Hardware Required

About Serial Monitor

Serial Monitor is one of the tools in Arduino IDE. It is used for two purposes:

• ESP32 → PC: Receives data from ESP32 and display data on screen. This is usually used for debugging and monitoring
• PC → ESP32: Sends data (command) from PC to ESP32.

Data is exchanged between Serial Monitor and ESP32 via USB cable, which is also used to upload the code to ESP32. Therefore, To use Serial Monitor, we MUST connect ESP32 and PC via this cable.

How To Use Serial Monitor

Open Serial Monitor

Click the Serial Monitor icon

Items on Serial Monitor

1. Output console: display data received from ESP32.

   
2. Autoscroll checkbox: option to select between automatically scroll and not scroll.

   
3. Show timestamp checkbox: option to show timestamp prior to data displayed on Serial Monitor.

   
4. Clear output button: clear all text on the output console.

   
5. Baud rate selection: select communication speed (baud rate) between ESP32 and PC. This value MUST be the same as the value used in ESP32 code (in Serial.begin() function).

   

   ※ NOTE THAT:

   When we select baud rate (even the value is not changed), ESP32 is reset. Therefore, this is one way to reset ESP32.

6. Textbox: user can type characters to send to ESP32

   
7. Ending selection: select the ending characters appended to data sent to ESP32. Selection includes:

   • No line ending: append nothing
   • Newline: append newline (LF, or '\n') character
   • Carriage return: append carriage return (CR, or '\r') character
   • Both NL and CR: append both newline and carriage return (CRLF, or '\r\n') characters

   
8. Send button: when the button is pressed, Serial Monitor sends data in textbox plus the ending characters to ESP32

   

ESP TO PC

To send data from ESP32 to PC, we need to use the following ESP32 code:

• Set baud rate and begin Serial port by using Serial.begin() function

  Serial.begin(baudrate);

• Send data to Serial Monitor using one of the following functions: Serial.print(), Serial.println(), Serial.write(). For example, send “Hello World!” to Serial Monitor

  Serial.println("Hello World!");

Example Use

In this example, we will send the “esp32io.com” from ESP32 to Serial Monitor every second

void setup() {
  Serial.begin(9600);
}
void loop() {
  Serial.println("Hello World!");
  delay(1000);
}              

Quick Steps

• power up your board
• Open Arduino IDE
• Select the right board
• Select the right port
• Copy the above code and open with Arduino IDE
• Click Upload button on Arduino IDE to upload code to ESP32
• Open Serial Monitor on Arduino IDE
• Select baurate 9600
• See the output on Serial Monitor

PC TO ESP

How to send data from PC to Aduino and read it on ESP32

You will type text on Serial Monitor and then click Send button.

ESP32 reads data and process it. To read data, we need to use the following ESP32 code:

• Set baud rate and begin Serial port

  Serial.begin(baudrate);

• Check whether data is available or not

  if(Serial.available())
  {
     // TO DO
  }

• Read data from Serial port using one of the following functions: Serial.read(), Serial.readBytes(), Serial.readBytesUntil(), Serial.readString(), Serial.readStringUntil(). For example:

  String data = Serial.readStringUntil("\r\n");

Example Use

In this example, we will send the commands from Serial Monitor to ESP32 to turn on/off a built-in LED. The commands include:

• “ON”: turn on LED
• “OFF”: turn off LED

How ESP32 can receive a complete command? For example, when we send “OFF” command, how ESP32 can know the command is “O”, “OF” or “OFF”?

When sending a command, we will append a newline character ('\n') by selecting “newline” option on Serial Monitor. ESP32 will read data until it meets the newline character. In this case, the newline character is called delimiter.

int led_pin = 13;
void setup() {
  Serial.begin(9600);
  pinMode(led_pin, OUTPUT);                                // set the digital pin as output:
}
void loop() {
  if(Serial.available())                                   // if there is data comming
  {
    String command = Serial.readStringUntil('\n');         // read string until meet newline character
    if(command == "ON")
    {
      digitalWrite(led_pin, HIGH);                         // turn on LED
      Serial.println("LED is turned ON");                  // send action to Serial Monitor
    }
    else
    if(command == "OFF")
    {
      digitalWrite(led_pin, LOW);                          // turn off LED
      Serial.println("LED is turned OFF");                 // send action to Serial Monitor
    }
  }
}              

Quick Steps

• power up your board
• Open Arduino IDE
• Select the right board
• Select the right port
• Copy the above code and open with Arduino IDE
• Click Upload button on Arduino IDE to upload code to ESP32
• Open Serial Monitor on Arduino IDE
• Select baurate 9600 and newline option
• Type “ON” or “OFF” and click Send button

• See your LED state. We will see LED's state is ON or OFF, respectively.
• We also see LED's state on Serial Monitor

Code Explanation

• configure an ESP32's pin to digital output mode by using pinMode() function.
• program the pin to GND to turn off led by using digitalWrite(pinNumber,LOW)
• program the pin to VCC to turn on led by using digitalWrite(pinNumber,HIGH)

Read the line-by-line explanation in comment lines of source code!

Book Tutorial

We are considering to make the book tutorials. If you think the book tutorials are essential, you can download it. download book

See Also

• ESP32 - Button
• ESP32 - Button - Debounce
• ESP32 - Button - Long Press Short Press
• ESP32 - Button - Relay
• ESP32 - Button Toggle LED
• ESP32 - Button Toggle Relay
• ESP32 - Button - Piezo Buzzer
• ESP32 - Button - Servo Motor
• ESP32 - Button Controls Electromagnetic Lock

References

• Arduino IDE
• ESP32