I am using an MG946R Servo.

When I use the power directly from the Arduino (Uno) and do a sweep, it works as expected.

However, when I replace the Arduino power with external power, the Servo either doesn't move or it moves randomly.

I've tried this with both a multi voltage power adaptor, setting the power to both 4.5V and 6V, as well as with a 4 x AA battery pack.

When I use a multi meter set at 6V and check the pins going into the Servo (when it's moving randomly) the voltage keeps moving to anywhere between 5.20V and 5.70V.

It seems that the Servo doesn't move when using battery pack, even though the voltage on the pins reads 5.75V.

Is there something that I am missing here?

  • Did you connect the grounds of both power supplies? This has to be done, when using more than one – chrisl Apr 1 '18 at 12:08
  • @chrisl, I'm only using one of the power supplies (adapter or batteries) at one time. – Daniel Gee Apr 1 '18 at 12:11
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    Can you show us your circuit? Where have you checked the voltage with the multimeter? At the supply voltage or at the PWM pin? – chrisl Apr 1 '18 at 14:46
  • @chrisl, sorry to waste your time. I figured it out. I needed to run connect the negative from the external power to the GND on the Arduino. (Which I hadn't done.) – Daniel Gee Apr 3 '18 at 2:15
  • What?! you have to connect BOTH grounds together? If the power supply to the arduino is a wall wart to its dc input and the power supply to the servo is another wall wart and both wall warts are plugged in to the same wall socket, arent the neutrals ALREADY connected? – aquagremlin Apr 25 '18 at 14:28

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