#include <Arduino.h>

#define RELAY_PIN 5   // D1 — relay shield IN; GPIO0 is a boot-strapping pin (must be HIGH at reset, else UART download mode)
#define LED_PIN LED_BUILTIN

void setup() {
  pinMode(RELAY_PIN, OUTPUT);
  pinMode(LED_PIN, OUTPUT);
  digitalWrite(RELAY_PIN, LOW);
  digitalWrite(LED_PIN, HIGH);
  Serial.begin(115200);
  Serial.println("Ready — send 1 (on) or 0 (off)");
}

void loop() {
  if (Serial.available() > 0) {
    char c = Serial.read();
    if (c == '1') {
      digitalWrite(RELAY_PIN, HIGH);
      digitalWrite(LED_PIN, LOW);
      Serial.println("ON");
    } else if (c == '0') {
      digitalWrite(RELAY_PIN, LOW);
      digitalWrite(LED_PIN, HIGH);
      Serial.println("OFF");
    }
  }
}