I have a project that involves sending messages from an Android device to an Arduino using a bluetooth module. I am using an HC-05 bluetooth module and an Arduino Mega 2560.

It works as long as I power the Arduino to my laptop using a USB cable. However, I need to use an external power source and have been using a 6F22 9V battery connected through the VIN pin for this purpose, without facing any problems. But on connecting the HC-05, it does not even light up.

The Arduino is also connected to four dc motors, five servo motors (all of which are externally powered, only get digital signals from the Arduino), and seven HC-SR04 ultrasound sensors, whcih are powered through the 5V pin.

I have connected the HC-05 to the Arduino as follows:

HC-05 Arduino

VCC 3.3V



RX TX through a voltage divider

I am new to all this, and would be grateful for any help. Thank you.

1 Answer 1


6F22 (PP3) batteries are among the wimpiest of batteries available. They are not a good choice for anything except extreme low power applications, and anything involving radio transmitters is definitely not an extreme low power application.

Use a better battery. I would recommend 6 AA batteries (you can get 6xAA battery holders with the same connector as a PP3 battery) which will give you considerably more power than a little PP3.

Either that or a 7.2V "2S" Li-Ion battery pack.

  • Thank you for the reply! Is the problem occurring because the current provided by the 6F22 is not enough?
    – GoodDeeds
    Jan 24, 2016 at 17:36
  • Quite possibly. Try a more powerful battery and see if the problem goes away.
    – Majenko
    Jan 24, 2016 at 17:37

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