Make your Arduino projects portable by using a battery for power.  From the Uno and Mega documentation pages:

"The board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts."

I've found that using 9V works well.  You can simply connect the + end of your battery to Arduino Vin and the - end to Arduino ground (fig 1).  You should see the green light on the Arduino turn on to indicate that it is powered.

It's also a good idea to attach a toggle switch in series with this battery so that you can turn your Arduino off and on.  As shown in the images above, solder a toggle switch to the red lead from the 9V battery connector.  Connect the black lead from the battery connector to one of the Arduino's ground pins, and connect the lead from the toggle switch to Arduino's Vin pin.  Snap a battery to the connector.  Now your Arduino will turn on when the switch is closed and turn off when it is open (figs 5 and 6).
funky819 months ago

Hi, thanks for your info. One question, is it possible to monitor battery voltage ?

if it's possible, do you mind to show it?


djmelvinv funky812 months ago
hi you can use two resistors as a voltage divider to go under the max 5v. then connect de pin between de resistors at an analog pin for example A0. Now you can map the analog value to you battery values. so 0-1024 mapped to 0-12 (when using a 12v battery).
amandaghassaei (author)  funky819 months ago

you can measure battery voltage with a voltmeter, is that what you mean?

Ahmedqatar4 months ago

Seem good but how long a battery may last??

thesonyman10111 months ago
arduino uno made a pop noise when i did this thankfully it still works
amandaghassaei (author)  thesonyman1019 months ago

be careful to get the connections right!

funky819 months ago

Hi, thanks for your info. One question, is it possible to monitor battery voltage ?

if it's possible, do you mind to show it?


stauhidi1 year ago
(removed by author or community request)
amandaghassaei (author)  stauhidi1 year ago
it will be fine. Try measuring the voltage after you've wired it up to the Arduino, you might find that the voltage comes down to 12V when a load (the Arduino) is applied to the battery.
ktitiz1 year ago
if you build gps or using something shield like lcd, you will get to 2 or more 9v battery,
mangopeach1 year ago
This is also a thing:
agupta521 year ago
Tried the same not working
Gelfling61 year ago
I've done similar, with a converted ATX supply, back-feeding +12V through the VCC pin. But, one word of warning, this still feeds back to the coaxial connector, then through the +5V regulator, and it's a thin trace on the bottom of the board. (all models from the Diecimila, to the present day Due and even the MEGAs,) I had to re-bridge this thin trace, when, powering a Duemilinove off the stock 9V battery pack, and a wire coming from the VCC pin, popped out of the breadboard, and touched a GND connection.. (Ironic, it was feeding a LM7805 regulator that was on the breadboard to power a couple of servos. guess what it touched? [o] )
myth212 years ago
hi i have one question...i have a buzzer that operates from 6-12v..and i put it on the arduino board that only produces 5v..and its working.. is it alright?wouldnt it damage my board??thanks
amandaghassaei (author)  myth212 years ago
use a multimeter to measure how much current the buzzer is drawing, if it is pulling close to 40 then maybe try using a transistor to source the current directly from your power supply. does that make sense?
A 9V to 2.1mm connector is less than $2.

Makes things far easier and way less complicated.
you can also take apart a used 9 volt and take the top piece with the connectors, solder wires to the back, solder those wires to a 2.1mm plug from an old power supply, and then cover the end with shrink tubing or epoxy. you just made one for free. I've already made a couple.
amandaghassaei (author)  bears02 years ago
cool, you should make a photo instructable and enter it in tips and tricks!
amandaghassaei (author)  JoshuaZimmerman2 years ago
it's not easier, now you need a plug and a snap battery connector and a switch. I like using the vin pin bc the barrel plug takes up a lot of space, if you want the arduino's usb port accessible to the outside you can't use the barrel plug, it's just too bulky.
Ahhh, see, now you're putting it into context. Like your box. That makes sense in your situation.

The way your write up is worded it just seems as if you've got your Arduino powered up by this method at all times for some odd reason. Which makes no sense and seems overly complicated.

Now that you've placed it in context with a larger project when you wish to keep the USB port flush with your case, everything falls into place.

Maybe you could go back into your write up and add a paragraph explaining WHY you've chosen to do this method and put in a picture of your box.
caitlinsdad2 years ago
There is the power supply jack at the end which takes a 2.1 mm barrel plug which makes a nicer connection.
I agree w/ you there, I prefer to keep all of my headers open for use.
In that case, i don't think you quite understand the sole purpose of the VIN pin. It's only reason for existence is to provide power from an external source with no connector plug. I personally like this better, as there are barely any wires in the way.
It is also good if you DO use the barrel plug as a safe way to hook up high-amp devices and not fry the board reg.