external power supply

hi, i just have two servos connected to the board… if i use the usb power supply to run the uploaded sketch everything appears ok… but when i disconnected the usb and use a 9v battery then it doesnt work anymore…

i noe this is a super noob qn… but please enlighten me! :’(

It could be the battery won’t supply enough current for the motors so try using a mains power supply.

Also depending on what sort of arduino you have you might have to change a lik to get it to power off Vin.

it didntwork... i used the mains at 12v or use the Vin and both didnt work after i uploaded my sketch.. i think it actually ran the blink led on pin13 example instead.. im using duemilanove..

what else can i try?

what else can i try?

What is the current rating of the 12v power module you tried to use?

Powering two servos and an Arduino requires a minmimum amount of current. The fact that you can power all that from the USB says you need at least 500ma of current or more, I wouldn't use an external power module or battery with less then 1 amp of current capacity for two servos and an Arduino and even that can be marginal is the servos are under mechanical load.


oh ok.. so its underpowered? i changed to an ac to dc adapater rated at 350mA max and connected at 12v.. it worked! i turned it down to 9V and it started to screw up.. so i guess that proves your point!

i cant imagine 2 servos and an arduino took so much power.. how do people get their projects running around without connecting to the com then? i cant use batteries?

how do people get their projects running around without connecting to the com then?

Not sure I understand that question. If using an external DC power source via the Vin pin then also the Arduino ground pin has to wire to the external power sources' negative terminal also. If you are using the Arduino's external power jack then both the positive and ground connections are being made through that jack.

Some use USB power for the Arduino board only and use an external 5vdc DC power supply for just the servo(s) 5vdc leads and also wire the external negative to the Arduino's ground pin. That make sense?

Servos have DC motors inside as well as circuitry and their current requirements are higher then you might think depending on the servo size and how much mechanical torque is being asked to be moved.


If your question is: how do people provide power to servo projects – I use USB to power the Arduino board but power the servos from an external regulated 5v power supply. I have a bunch of surplus wall warts that were used to power various external computer peripherals (mostly Ethernet switches and routers).

i see.. thanks for the answers!

what i meant earlier was how to let the project be mobile and carry its own power supply around.. if u r using mains or usb connection to the computer when running servos doesnt it mean u r limited to the length of the wire?

A portable Arduino project would require a portable power source, batteries being the most normal solution. There are all kinds of rechargeable batteries that can be sized to provide any current capacity required, it's just a matter of the dollars and size budget you have.


thank you people for answering!