I am trying to control the LED on pin13 using the below code but it's not working. With this code I am able to print to the Serial Monitor but the code has no effect on the any of the digital pins. I am unable to control the LED and so I have gotten stuck and can't advance further. I can't understand why it is happening even if I have excluded the new line from the Bluetooth app that I am using to send the strings and same on the Serial Monitor.

#include<SoftwareSerial.h>          // import the serial library

SoftwareSerial bluetooth(6, 7);     // RX, TX

void setup(){
  Serial.begin(9600);               //set baud rate
  pinMode(13, OUTPUT);
  digitalWrite(13, LOW);

void loop(){
  while (bluetooth.available()){
    char ch = bluetooth.read();
    message += ch;

    if(message != ""){
        digitalWrite(13, HIGH);
        digitalWrite(13, LOW);
      message = "";
  • What is the output of the serial terminal? That is exactly what is reaching the code, so this would help alot. I will update my answer, when you provide more information. Also: How have you connected the HC-05? Did you use a voltage divider for it's RX line? (The HC-05 works with 3.3V and most Arduino boards with 5V) And the if-statement if(!bluetooth.available()) isn't necessary here, because when you are leaving the while loop there is nothing available, unless it is received on this few clock cycle of the execution between. – chrisl Jan 24 '18 at 9:33
  • the serial monitor outputs "on" as 'o' and 'n' in separate lines. bluetooth terminal on my phone doesn't print anything. But the code works fine if I am using the normal (Rx,Tx) pins, the terminal on my phone also prints the strings it sends,that works fine even without the voltage divider. I just don't want to engage the pins(1,2). I don't know if there is a problem with the SoftwareSerial library – Sudhanshu Shivam Jan 24 '18 at 11:04
  • 1
    the chars come slower over SoftwareSerial and your code doesn't wait for them. if next char is not available immediately you continue in loop – Juraj Jan 24 '18 at 12:15
  • please elaborate I tried while(blurtooth.available()==0); to wait for the data but that is not working; – Sudhanshu Shivam Jan 24 '18 at 13:55
  • I was basically getting the problem due to some garbage values flowing in and I managed that by using if(message.substring(0,2).equals("on")). and now it works fine – Sudhanshu Shivam Jan 24 '18 at 19:18

Your logic is a complete mess. You have:

  1. If a character is available, read it and add it to message.
  2. If another character is available, compare what you have already stored with on.
    • If it's equal ('o' is not equal to 'on') turn on, otherwise turn off.
    • Print what you have stored.
  3. Forget what you stored
  4. Go to 1 (a character is still available since you never read it in stage 2).

Instead you need something more like:

  1. If a character is available, read it into a variable.
  2. If the character you read is a line ending character:
    • Compare your message with 'on' and take appropriate action
  3. If the character you read is not a line ending character:
    • Add the character to message.
  4. Go to 1.

Note how you only check once if there is a character available, and all your testing is done within that one if block.

  • so i basically tried that but it's not working – Sudhanshu Shivam Jan 24 '18 at 14:00
  • 1
    Comments are not places to dump code. – Majenko Jan 24 '18 at 14:01
  • really srry about that – Sudhanshu Shivam Jan 24 '18 at 14:02

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