arduino uno上传代码：

int i ;
void setup() {

  Serial.begin(115200);
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(4, OUTPUT);
}

void loop() {
  if (Serial.available())
  {
//    Serial.write(Serial.read());
    i = Serial.read();
//    Serial.println(i);
      Serial.write(i);
      Serial.write('\n');
  }

  if (i == 'a')
  {
    digitalWrite(2, HIGH);
  }
  if (i == 'b')
  {
    digitalWrite(3, HIGH);
  }
  if (i == 'c')
  {
    digitalWrite(4, HIGH);
  }
}

esp32cam上传代码：

//This example code is in the Public Domain (or CC0 licensed, at your option.)
//By Evandro Copercini - 2018
//
//This example creates a bridge between Serial and Classical Bluetooth (SPP)
//and also demonstrate that SerialBT have the same functionalities of a normal Serial

#include "BluetoothSerial.h"

#if !defined(CONFIG_BT_ENABLED) || !defined(CONFIG_BLUEDROID_ENABLED)
#error Bluetooth is not enabled! Please run `make menuconfig` to and enable it
#endif

BluetoothSerial SerialBT;

char i;

void setup() {
  Serial.begin(115200);
  SerialBT.begin("ESP32test"); //Bluetooth device name
  Serial.println("The device started, now you can pair it with bluetooth!");
}

void loop() {
  // 蓝牙助手发送数据到电脑串口
  if (SerialBT.available()) {
    while (SerialBT.available()) {
      //      Serial.write(SerialBT.read());
      //读一个就少一个
      i = SerialBT.read();
      Serial.print(i);
    }
  }

}