Bluetooth HC-05 not responding while connected

I have been using a Arduino UNO and an Arduino Leonardo with a HC-05 bluetooth module. I had it working a few weeks ago just using the simple example and a youtube video on how to connect (Just using simple D13 pin to turn LED on/off. Button

I have the bluetooth connection. (module changes to slow blinking)
I have tried 3 different modules to make sure they are good…
I have tried 2 different boards (UNO and Leonardo)
Double checked connections…
Double checked auth code…

Serial monitor doesn’t work (set to 9600 for debug serial and serial.begin set to 38,400 per HC-05 default)…

Everything was working before. I decided I wanted to add a slider and some other code (I am not a novice coder) and it just stopped showing connection. The device shows connection to phone, but Blynk app shows read indicator on “chip” logo. Sometimes, I click on it and it will say “Wasn’t online yet”… sometimes it says it is. Either way… it doesn’t do anything.

I have deleted app and started from scratch many times.

One thing I have noticed, is after I load the example code for the HC-05 onto the boards, I have horrible issues connecting back to the board again. I literally have to restart the PC each time. I can do “Get board info” and it works but it always says “can’t find board” if I try to load anything. This happens ONLY if I load the HC-05 example code. Every other example code works fine with no restart issues.
I have tested this on 3 different PCs running windows.

Any ideas?

Phone O/S & version?
Blynk library version?


Phone is Google Pixel 3… Updated OS
Blynk Library is latest version 0.6.1
Code is just the arduion example given by Blynk for HC-05

  Blynk is a platform with iOS and Android apps to control
  Arduino, Raspberry Pi and the likes over the Internet.
  You can easily build graphic interfaces for all your
  projects by simply dragging and dropping widgets.

    Downloads, docs, tutorials:
    Sketch generator: 
    Blynk community:  
    Social networks:  

  Blynk library is licensed under MIT license
  This example code is in public domain.

  This example shows how to use Arduino with HC-06/HC-05
  Bluetooth 2.0 Serial Port Profile (SPP) module
  to connect your project to Blynk.

  Note: This only works on Android! iOS does not support SPP :(
        You may need to pair the module with your smartphone
        via Bluetooth settings. Default pairing password is 1234

  Feel free to apply it to any other example. It's simple!

  NOTE: Bluetooth support is in beta!



// You could use a spare Hardware Serial on boards that have it (like Mega)
#include <SoftwareSerial.h>
SoftwareSerial DebugSerial(2, 3); // RX, TX

#define BLYNK_PRINT DebugSerial
#include <BlynkSimpleSerialBLE.h>

// You should get Auth Token in the Blynk App.
// Go to the Project Settings (nut icon).
char auth[] = "YourAuthToken";

void setup()
  // Debug console

  DebugSerial.println("Waiting for connections...");

  // Blynk will work through Serial
  // 9600 is for HC-06. For HC-05 default speed is 38400
  // Do not read or write this serial manually in your sketch
  Blynk.begin(Serial, auth);

void loop()

And your Blynk app version.
(Basically, all the stuff that you were asked to provide when you created the new thread…)

  1. Add details :
    • Hardware model + communication type. For example: Arduino UNO with Ethernet Shield
    • Smartphone OS (iOS or Android) + version
    • Blynk server or local server
    • Blynk Library version


Hardware is already stated… Arduino Uno or Arduino Leonardo with HC-05 Module (Working 3 weeks ago when last checked)

Smartphone is Google Pixel (Apple does not work with HC-05 Bluetooth serial) running Android 9

Blynk library is 0.6.1 as already stated.

Server version. Nothing local has ever been installed.

Five posts in (six if you count the one in the other topic) and we still don’t know which version of the Blynk app you’re running.

I give up.


Sorry, the Blynk app would be 2.27.8… or the latest available for Google Pixel device (automatic update).