#include <SoftwareSerial.h>
    SoftwareSerial BTSerial(2, 1); //(TX,RX)
    
    int btn = 4;
    void setup() {
        pinMode(btn, OUTPUT);
        digitalWrite(btn, HIGH);
        //Serial.begin(9600);
        BTSerial.begin(9600);
        pinMode(btn, INPUT);
    }
    void loop() {
        char data;
        byte value;
        value = digitalRead(btn);
        if(value == 1){
        data = '1';
        }else{
        data = '0';
        }
        BTSerial.print(data);
        BTSerial.write("\n");
        //Serial.println(data);
        delay(500);
    }