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ITS URGENT! Arduino not working with external power supply? Answered

I have made arduino uno u3 robot, i have used 2 geared motors via a l293d using one 9v battery and tried power the arduino with a 9v battery, then with 9v adapter but it did'nt work, I also tried powering the board via the Vin pin, also through the usb cable using the 9v batterg and adapter, but it didnt work either.when i plug it to the laptop with usb everything works very fine. Please give me a sol. soon urgent i hav the exhibition after 3 days!!


So the UNO is still working on USB ?

a 9V battery isn't likely to run the thing, and the motors.

What did you use for the 9V adapter ?

Show your circuits.


it only and only works when i connect the board to the pc via usb cable.
if i try to power it with a battery through the usb jack, it doesnot work.
the adapter is simply a regulated 9v supply from a rectifier.
the motors are connected from l293d, with 6v regulated power.(on bread board)
the servo is connected on the breadboard.
i have made the ground common for all..

plsssss....suggest me something...

instrctables is not letting me upload a pic..sry.

Can't help without a diagram, sorry.

DON'T POWER IT THROUGH THE USB JACK !!! Not with a 9V supply !!!!!

I have same problem as Ankan but with 6V instead of 9.
I made a arduino car robot with arduino uno (shields on it), sharp IR-sensor, 2DC motors, 4AA battry and 2 limited switch.

When I connect the arduino with the cable, it works fine! all the functions work and I don't see any errors. However once I try to let it work through external power supply (4aa) it doesn't work at all. The power light lights up but that's it. I think I would need to use resistor for each limited switch but I have no clue which resistors I should use and I am not certain if it will solve this problem either. Please help me because I am getting so hopeless. Thank in advance.

PS - I tried this method but it seems like it's not working at all
V = R * I, or solved for R, R = V / I
R = 6 volts / 0.030 amps
R = 200 ohms --> 220 resistor

my breadboard are based on this fritzing sketch (the code is made by me and it works without a problem)

Show me a circuit diagram, not a pretty picture. The usual problem is missing a ground somewhere.

I have noticed same with my nano V3. The sketch works perfectly when it is connected through usb by pc or using a mobile charger adapter with USB connection.

As soon as i power it using Vin pin and ground with regulated 12V supply or even a 9V battery, it works crazy i.e. the sketch is not running at all.

As soon as i again power is through USB jack, it works perfectly.

this is very strange... any clues.. suggestions ?

I had make mistake in wiring as mentioned in my earlier post.

Just check...sometimes we very simple mistake due to oversight.

I solved the problem.

i noticed that by mistake i had connected a resistor between ground pin of my nano and ground of my powersupply.

i removed it and now it works perfectly.

Just a small point - The 293 will only power small motors - about 800MA then it automatically cuts off. This gives the appearance that it isn't working.

I aghree with the others as well.

That fact alone is likely to kill his 9V battery. "For the want of the nail"

An Arduino Uno can be powered by

  • a stable (regulated) 5V DC, which you can either supply via the USB power lines, or via the shield connectors, or
  • an unregulated 6-20 V DC (7-12V recommended), which you can supply via the 2.1 mm centre-positive barrel plug connector.

I would not recommend using a 9V battery, because its voltage will drop quickly, but in a pinch this can be used.

ref: http://arduino.cc/en/Main/ArduinoBoardUno

Absolutely, and there is very little chance the 9V battery will run motors anyway.