# Question from a newbie about power supplies...

So my ever-varying university course has ended up requiring me to wire up an arduino and a servo to a power supply, with very limited elecronics knowledge.

I have a variable voltage power supply that will give both 6V and 9V, and worked out enough to plug the thing into the arduino and turn it on sucessfully. Thing is, I want to use the same power supply to power my servo, which runs on 6V.

I’ve managed to work out that the arduino and the servo need to have a common ground (link the negative power wire to GND) but can i just link the positive and negative wires of the servo to the positive and negative power wires if the power supply is giving 6V? If i give the servo 7.5 volts to increase stability of the arduino will it fry it?

I’m a bit confused >_< Any pointers would be greatly appreciated! Many thanks

You can power the arduino from 9 volts and the servo from 6 volts. As you say, the ground from the power supply, arduino and servo must all be connected together. Many servos will not handle more than 6 volts so I would not tray any higher than that unless you have reliable information that your servo can cope.

my ever-varying university course

What do your teachers tell you to do? If not, why not?

I guess is also depends on WHICH Arduino you are using.

It's a masters course, and the tutor isn't here today. Really useful when the thing is due thursday.

OK, i understand about the different power requirements of the servo and the arduino, what i'm asking is if it's possible to run them both off the same power supply, at 6V, by connecting the wires somehow?

It's an Arduino Diecimila?

Connect the grounds together. Just the grounds. Power the Arduino (Vin) from 9V, the red wire of the servo from 6V. But before you connect anything, check the outputs of the supply with a DC multimeterr set to an appropriate range, and make sure you don't have any surprising minus signs.

That sounds great! So, in newbie speak, put the red wire from the servo into the little hole with "5v" written by it on the power section of the arduino? Then put the black wire of the servo connected to the negative wire of the power supply and link that to the GND hole. Then put the positive wire of the power supply where? linked to the positive of the servo also?

ah! the Vin, not the 5v hole. Can that be 6v?

If the power supply has two outputs, one for 6v and the other for 9 then connect as follows:

Black (may be brown) servo wire to Arduno Gnd and power supply Gnd. Red (center) servo wire to power supply 6 volts White servo wire to arduino pin Arduino external power input (9 volt or Vin ) to power supply 9 volts.

The Arduino reference pages has more info on Arduino power pins: http://www.arduino.cc/en/Main/Hardware

the Vin, not the 5v hole. Can that be 6v?

6V is not enough for sane operation; between the regulator overhead and the protection diode you need a minimum of 7.6V at Vin.

The arduino may run on 6V at Vin, but if you try to download a sketch you may corrupt the bootloader and require an ICSP programmer to get it back. Been there, done that.

-j

If the servo won't have anly load on it (ie... the servo is not moving anything other than the servo arm) and your arduino has a 5v pin I would just connect the servo to that for power.

If you dont have a 5v pin or you plan on doing something with the servo that might put a load on it I'd say you'd need to build a power supply at that point.

I've flown many a R/C plane (4+ servos) on a 4.6 volt pack. The serovs can handle up to 6 volts and you get the best performance at 6v but it's not required. If you just have to have 6v, go to your local hobby shop and get a voltage regulator and hook up your 9 volts to it.

Hope that helps.

Thankyou for all your help! I've decided to run the arduino from my computer and just power the servo externally to prevent more headache than it needs. I'll connect the grounds as advised. What a helpful forum! thankyou everyone :D

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.

That's the official party line. Unless your project has to work in outer space, you should be fine running at 6V. ;)

Wohoooo! it works! so happy XD