Servo motor issue when using 9V battery

Hi,

I have created an automatic guitar tuner and it works perfectly when the Arduino is plugged via USB into the computer. As soon as I use an external power supply like a 9V battery or 9V DC wall plug the servo motor starts to act up. In my code I have the motor not move when not in use (depending if a guitar signal is received or not). The motor moves and does funny things even though the code tells it not to move.

What is the main difference between the USB power and a 9V battery power? Anyone else ever experienced this problem or have any ideas for me to troubleshoot?
Thanks in advance,
Scott

Those small 9vdc batteries are useless for powering servos, they don't have the current capacity. However an external wall powered 9vdc transformer could work if it has a 1 amp current rating or higher.

Lefty

Thanks, that's what I was going to try next as the 9V DC wall adapter I have now only goes to 500mA. Thanks for the reply and insight :-)

Make sure common grounds are connected.

As soon as I use an external power supply like a 9V battery or 9V DC wall plug the servo motor starts to act up.

If you are trying to directly power the servo with 9v, you may ruin the servo. Most servos are rated for 4.8v-6v.