HC-05 Bluetooth Module Blinking Red Light-Arduino Uno

Question

I have looked on google for an answer to my problems to no avail. The you tube video I am following is here: https://www.youtube.com/watch?v=f1v0IMegCvU So basically on my android, I can't see the HC-05 device show up and the module itself is flashing red unlike the video's flashing blue light. I have connected the circuit exactly like he has in the video with the 2 10K resisters. I am using the same app. What is wrong? Here is my code as I copied from the video.

void setup() 
{
  pinMode(13, OUTPUT);
  Serial.begin(9600);
  Serial.println("Connection Successful!");
}
void loop() 
{
  if(Serial.available()>0){
    int data=Serial.read();
    switch(data){
      case 'a': LEDON();break;
      case 'b': LEDOFF();break;
      default : break;
    }
  }
  delay(50);
}
void LEDON(){
  Serial.println("Led On!");
  digitalWrite(13,HIGH);
}
void LEDOFF(){
  Serial.println("Led Off!");
  digitalWrite(13,LOW);
}

I also get the error avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x00 when connected through usb. I do not get any errors when just flashing the arduino without any wires connected to the arduino. I know that the port is correct. Any ideas would be helpful. Thanks.

Answer 1

There are several issues to consider:
• Program downloading
• HC-05 serial communication
• Bluetooth pairing

For the first issue: The serial-over-USB connection between the development computer and the Uno ties up the Uno's hardware serial RX and TX pins. There will be a conflict if the development computer transmits when the HC-05's TX is connected to the Uno's RX. This can be resolved by disconnecting the HC-05 TX when downloading a program.

For the second issue: The Uno schematic shows 1KΩ resistors between TX and RX on the ATmega328P and RX and TX on the USB chip (ie on an ATmega16U2, or a CH340, etc). If the HC-05's TX drive is strong enough, it will overcome the drive from the USB chip and work ok. Note, I would leave out the voltage divider (on the HC-05 RX line) that the video shows.

For the third issue: The HC-05 in the video mentioned in the question has a blue LED that blinks steadily when the HC-05 isn't paired, and blinks at a long interval when it is paired. Many HC-05's have red LEDs instead of blue; the LED color is not an issue. Some HC-05's don't blink at all when paired; that's not an issue either. What is an issue is that (according to description in question) your HC-05 keeps on blinking, so apparently isn't paired up.

Whether the HC-05 pairs with an Android app is more or less independent of whether you have the HC-05 connected to an Arduino; you should be able to pair your phone with the HC-05 when just Vcc and ground are connected to the HC-05. If you are having trouble with pairing, try another app; try powering the HC-05 down and up; and try a different HC-05. I mention trying another app because one serial-terminal app I installed on my Android phone needed the app or the HC-05 to be restarted to pair up after loss of pairing, and the serial-terminal app I replaced it with did not need those actions. Note, pairing takes a few steps on my phone: in Settings / Wireless, search for Bluetooth devices; select device; enter its passcode; run an app and tell the app which Bluetooth device to use.

Answer 2

Try this code(it's simpler):

char data ;
void setup()
{
    Serial.begin(9600);                             
    pinMode(13, OUTPUT);  
}
void loop()
{
   if(Serial.available() > 0)      
   {
      data = Serial.read();        
      Serial.print("\n");        
      if(data == '1')     
      {         
         digitalWrite(13, HIGH);
         Serial.print("on");
      }
      else if(data == '0')         
      {
        digitalWrite(13, LOW);  
        Serial.print("off");
      }
   }
}

Upload this to your Arduino. Open your phone, go to bluetooth settings and connect to HC05 with password 1234. Download an app from here: https://github.com/Mayoogh/Arduino-Bluetooth-Basic Now your circuit should work. Arduino to HC05 connections: 5V -> 5V GND-> GND RX -> TX TX -> RX LED connection: connect LED to pin 13 and the GND pin beside it(it's fine if you don't use resistor).