Can anyone please help me figure out/ point the reason of this arduino problem? I uploaded a simple arduino sketch (blink an LED ) just to test if my real program was the reason of the "abnormality" of this board. It works fine when I connected it to PC via arduino cable, but doesn't run the program when I use an external power supply(9v) and connected it to the Vin pin of arduino.

Need help and hoping for fast replies. I will be having a competition tomorrow, this is very urgent. please guys.

for the schematic diagram, there are no other parts inserted to the arduino board, aside from the 9v battery. I was able to say that the program work on "LED blink" by observing the lights of "TX" LED on the board. please help me. :(

  • 1.) What Arduino do you use? Each Arduino can have different voltage regulator. 2.) Use another method to observe your Arduino. TX LED is blinking because of communication. It wont blink if there are no communication from Arduino. You can use LED_BUILTIN pin to observe it
    – dhimaspw
    Nov 17 '16 at 2:54
  • that link for video is complete the same situation as mine. (that is not me on the video) I used arduino uno. thanks :)
    – Ellimenopy
    Nov 17 '16 at 2:56
  • Try this, and tell if its blink or not when you used external power supply : arduino.cc/en/tutorial/blink
    – dhimaspw
    Nov 17 '16 at 2:58
  • 1
    Thanks! It worked. LED blinks with 9V external power supply. hope that this would work with my program as well?
    – Ellimenopy
    Nov 17 '16 at 3:11

TX LED is blinking because of communication (indicating data transmit via serial). It will not blink if there are no communication from Arduino through USB cable.

For simple observation, use LED_BUILTIN pin. Its a build in-LED indicator on Arduino.



digitalWrite(LED_BUILTIN, HIGH);
digitalWrite(LED_BUILTIN, LOW);

Arduino fail on external power supply is usually because of voltage drop or your system draw too much current.


There is a possibility that you blew the regulator circuit with too much current while supplying your Vin pin with the 9V source. This would depend on your system power draw; something that you were using the board with before the blinker program - and also what kind of board you have.

To check this, try another similar board with the blinker program and the same 9V source. Don't forget to make the changes as suggested in the previous answer. The other problem could be your power source: to check whether your power source supplies the desired volts, measure the power source terminal voltage while connected to the board. Most boards will have the minimum voltage requirement on Vin, depending on their regulator design.

  • A 9V battery can't supply enough current to blow up a regulator.
    – Gerben
    Nov 17 '16 at 13:29
  • 1
    Would be interesting to know what facts you based that claim on. A 9v battery has enough juice to supply 0.5A for an hour so do the math. For the Uno's regulator 1A is enough, even if for a millisecond. Nov 17 '16 at 16:10
  • I think you are looking at the mAh rating, not the A. Duracell's 9V will drop to 5V after almost 2 hours at 250mA. You need at least 6-7V for the regulator.
    – Gerben
    Nov 17 '16 at 17:06
  • 1
    Agreed, but the point is to damage the protection diode on the regulator you just need a transient high current. Nov 17 '16 at 17:31

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