//code made by Elena Cardiel
#include <SoftwareSerial.h>
SoftwareSerial serial_relay(A5, A4); //tx, rx

const int relay = 3;
 
void setup() {
  serial_relay.begin(9600);
  pinMode(relay, OUTPUT); //relay = output
}

byte average;
 
void loop(){
  if (serial_relay.available() > 0) { // if we are receiving data from de sensor...
    average = serial_relay.read();
    if (average > 100) {
       digitalWrite(relay, HIGH); // relay on
    }
    else if (average <= 100) {
      digitalWrite(relay, LOW); // relay off
  }
}
}