# servos and external power

I have 2 continues rotation servos, I'm thinking they will need to be powered by a external power supply. so I did research and found you can use 4 double AA's (6 volts) I'm thinking that should be ok for servos . now if I wanted to power the ardunio with those same battery's that the servos are using (through regulated barrel plug) would that be ok with the ardunio or would it burn out or something cause the battery's ground will have to be wired to ardunio for servos

am I going about this the wrong way? is there a more efficient method for having less battery's ?

No, that should work ok; just draw the power for the servos directly from the battery and not from the Arduino’s on-board regulator (not enough current capacity there). The only real question is which Arduino are you using? The newer Arduino’s (from what I gather) have a lower dropout voltage regulator that can operate at 6 volts (?), while the older ones needed at least 7 volts to work properly.

while the older ones needed at least 7 volts to work properly.

Even the newest ones appear to require around 7 volts, due to the auto-voltage switching threshold, which is External voltage value minus one diode drop, divided by 2, must be higher then 3.3vdc, that is wired to one input of the voltage comparator circuit.

Lefty

retrolefty:

while the older ones needed at least 7 volts to work properly.

Even the newest ones appear to require around 7 volts, due to the auto-voltage switching threshold, which is External voltage value minus one diode drop, divided by 2, must be higher then 3.3vdc, that is wired to one input of the voltage comparator circuit.

Lefty

Hmm - I just keep hearing about people using the Uno at 6 volts, but maybe they're talking about a "non-standard" design or something using a lower dropout regulator? Not sure...

Hmm - I just keep hearing about people using the Uno at 6 volts, but maybe they're talking about a "non-standard" design or something using a lower dropout regulator? Not sure...

It's not about the regulator, or it's drop-out value, it's about the proper functioning of the auto-voltage switch the arduino uses to isolate the USB voltage (if present) if external voltage is also applied. Check out device U1A and it's input conditions in the below linked drawing.

However I have no doubt that if one plugs in 6vdc to the external connector the board will run, however there won't be proper isolation of the USB power when and if one plugs in to the USB for uploading or serial communications at the same time the external voltage is active.