#include <Wire.h>

#define SLAVE_ADDR 8  // 从机地址

void setup() {
  Wire.begin();         // 初始化 I2C 主机
  Serial.begin(9600);   // 串口监控
  Serial.println("Master ready. Press 'A' to turn ON LED, 'B' to turn OFF LED on slave.");
}

void loop() {
  if (Serial.available() > 0) {
    char c = Serial.read();
    if (c == 'A' || c == 'B') {
      Wire.beginTransmission(SLAVE_ADDR);
      Wire.write(c);       // 发送字符
      Wire.endTransmission();
      Serial.print("Sent: ");
      Serial.println(c);
    }
  }
}