#include <Wire.h>

#define SDA_PIN D0
#define SCL_PIN D1
#define LED_PIN D8 // D5 for Secondary 2

#define MY_ADDRESS 0x01  // 0x02 for Secondary 2

void receiveEvent(int howMany);

void setup() {
    pinMode(LED_PIN, OUTPUT);
    Wire.setSDA(SDA_PIN);
    Wire.setSCL(SCL_PIN);
    Wire.begin(MY_ADDRESS);
    Wire.onReceive(receiveEvent);
    Serial.begin(115200);
    Serial.print("Secondary at 0x");
    Serial.print(MY_ADDRESS, HEX);
    Serial.println(" ready.");
}

void loop() {
}

void receiveEvent(int howMany) {
    while (Wire.available()) {
        int cmd = Wire.read();
        if (cmd == 1) {
            digitalWrite(LED_PIN, HIGH);
            delay(1000);
            digitalWrite(LED_PIN, LOW);
        }
    }
}