External Power for Servo - Quick wiring question.

Got my first Arduino today and it is up and running beautifully. I plan on driving some high-powered servos and would like to do so using using external power for the servos while running the Arduino off of a 9volt battery. For the external servo power I'll be using a 6 volt gel cell (4Ah) batteries for untethered work and a regulated 6v PS for tethered. I'm sure I can figure out how to regulate the battery it so I don't jack up the servos, but I'm not sure about the wiring of servo+battery+arduino ground.

I'm assuming I hook up the servo's yellow wire to a pwm pin on the Arduino, and the servo's Pos wire to the battery's positive terminal only. Do I:

(A) Connect only the servo's ground to the Arduino's ground or;
(B) Connect BOTH the servo's ground and the battery's negative terminal to the Arduino's ground? Or;
(C) Have I got it completely wrong?

:slight_smile:

Normally I'd just try connecting things from least to most dangerous until it worked, but I don't want to fry the Arduino!

Also if anyone wants to give me a quick rundown of how to regulate the battery to no more than 6v, that would be awesome as well!

Thanks for your help!

All grounds get connected together. (B)

I'm assuming I hook up the servo's yellow wire to a pwm pin on the Arduino

With the latest version of the Arduino Servo library you can use any pin. Don't use the PWM from analogWrite to drive a servo.

Also if anyone wants to give me a quick rundown of how to regulate the battery to no more than 6v

You could simply put a diode in series (between the positive battery terminal and the servo positive power connector). This will reduce the voltage by around 0.7 volts so a fully charged battery should be giving not much more than 6 volts and still provide enough voltage for the servo when the battery runs down. A 1 amp diode (1N4001) would be a good choice.

A more efficient (and much more complicated) approach is to use a switching dc to dc converter (such as buck converter) but this is probably overkill for your application.

how to regulate the battery to no more than 6v,

You need a regulator, either a liner regulator like the ones shown here:-

These burn up power in the form of heat.

The other thing you can go for which is more efficient is a switching regulator or DC to DC converter like these:-

However these are more expensive. Also you could use on of these to produce 5V and go straight on the 5V input of the Arduino without going through it's regulator.

Also see:- http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html

Awesome replies, thank you!