arduino 用iic 方式连接lcd，比较省连接线，4根就够了。

安装arduino Arduino IDE 1.8.13

在库里在线查找，https://github.com/johnrickman/LiquidCrystal_I2C他的库，然后安装，这里是1.1.2版

然后运行下面的代码就可以正常显示字符了。

#include <Wire.h> 
#include <LiquidCrystal_I2C.h>
 
LiquidCrystal_I2C lcd(0x27,16,2); // set the LCD address to 0x27 for a 16 chars and 2 line display
 
void setup()
{
lcd.init(); // initialize the lcd 
lcd.backlight(); //Open the backlight
lcd.print("Welcome to "); // Print a message to the LCD.
lcd.setCursor(0,1); //newline
lcd.print("freeloong.top");// Print a message to the LCD
}
void loop()
{
}

这库里有example，

//YWROBOT
//Compatible with the Arduino IDE 1.0
//Library version:1.1
#include <Wire.h>
#include <LiquidCrystal_I2C.h>

#if defined(ARDUINO) && ARDUINO >= 100
#define printByte(args)  write(args);
#else
#define printByte(args)  print(args,BYTE);
#endif

uint8_t bell[8]  = {0x4,0xe,0xe,0xe,0x1f,0x0,0x4};
uint8_t note[8]  = {0x2,0x3,0x2,0xe,0x1e,0xc,0x0};
uint8_t clock[8] = {0x0,0xe,0x15,0x17,0x11,0xe,0x0};
uint8_t heart[8] = {0x0,0xa,0x1f,0x1f,0xe,0x4,0x0};
uint8_t duck[8]  = {0x0,0xc,0x1d,0xf,0xf,0x6,0x0};
uint8_t check[8] = {0x0,0x1,0x3,0x16,0x1c,0x8,0x0};
uint8_t cross[8] = {0x0,0x1b,0xe,0x4,0xe,0x1b,0x0};
uint8_t retarrow[8] = {	0x1,0x1,0x5,0x9,0x1f,0x8,0x4};
  
LiquidCrystal_I2C lcd(0x27,20,4);  // set the LCD address to 0x27 for a 16 chars and 2 line display

void setup()
{
  lcd.init();                      // initialize the lcd 
  lcd.backlight();
  
  lcd.createChar(0, bell);
  lcd.createChar(1, note);
  lcd.createChar(2, clock);
  lcd.createChar(3, heart);
  lcd.createChar(4, duck);
  lcd.createChar(5, check);
  lcd.createChar(6, cross);
  lcd.createChar(7, retarrow);
  lcd.home();
  
  lcd.print("Hello world...");
  lcd.setCursor(0, 1);
  lcd.print(" i ");
  lcd.printByte(3);
  lcd.print(" arduinos!");
  delay(5000);
  displayKeyCodes();
  
}

// display all keycodes
void displayKeyCodes(void) {
  uint8_t i = 0;
  while (1) {
    lcd.clear();
    lcd.print("Codes 0x"); lcd.print(i, HEX);
    lcd.print("-0x"); lcd.print(i+15, HEX);
    lcd.setCursor(0, 1);
    for (int j=0; j<16; j++) {
      lcd.printByte(i+j);
    }
    i+=16;
    
    delay(4000);
  }
}

void loop()
{

}

可以试试。

下面的代码：接受串口消息并显示

/*
 * Displays text sent over the serial port (e.g. from the Serial Monitor) on
 * an attached LCD.
 * YWROBOT
 *Compatible with the Arduino IDE 1.0
 *Library version:1.1
 */
#include <Wire.h> 
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27,20,4);  // set the LCD address to 0x27 for a 16 chars and 2 line display

void setup()
{
  lcd.init();                      // initialize the lcd 
  lcd.backlight();
  Serial.begin(9600);
}

void loop()
{
  // when characters arrive over the serial port...
  if (Serial.available()) {
    // wait a bit for the entire message to arrive
    delay(100);
    // clear the screen
    lcd.clear();
    // read all the available characters
    while (Serial.available() > 0) {
      // display each character to the LCD
      lcd.write(Serial.read());
    }
  }
}

open the backlight by serial:

/*
 * Displays text sent over the serial port (e.g. from the Serial Monitor) on
 * an attached LCD.
 * YWROBOT
 *Compatible with the Arduino IDE 1.0
 *Library version:1.1
 */
#include <Wire.h> 
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27,20,4);  // set the LCD address to 0x27 for a 16 chars and 2 line display

String cmd="";

void setup()
{
  lcd.init();                      // initialize the lcd 
  //lcd.backlight();
  Serial.begin(9600);
  Serial.println("my serial is ready to receive");
}

void loop()
{
  while (Serial.available() > 0){
    cmd += char(Serial.read());
    delay(10);//等待延迟
    }
  if (cmd.length() > 0){
    if (cmd == "on"){
      lcd.backlight();
      lcd.clear();
      lcd.print(cmd);
      cmd = "";
      }
    else{
      lcd.clear();
      lcd.print(cmd);
      cmd = "";
    }
    }
}