void setup() {
Serial. begin(115200);
pinMode(23,OUTPUT);
pinMode(21,OUTPUT);
pinMode(4,OUTPUT); 
}
void loop() {
Serial. println("hello ESP32!");
digitalWrite(23,HIGH);
delay(1000);
digitalWrite(23,LOW);
digitalWrite(21,HIGH);
delay(2000);
digitalWrite(21,LOW);
digitalWrite(4,HIGH);
delay(3000);
digitalWrite(4,LOW);
}