I have a 2 button midi controller built and it works great when the arduino is connected to the host computer from which I drew the sketch from. As soon as I connect power from anywhere else other than my laptop I cannot get anything to work or a get some much signal interference through the the midi cable it's unreadble. Please help. These are the combinations I have tried.
USB power from laptop (which sketch was uploaded) works great
USB power from desktop- sends signal interference through midi cable
12v wall wart power supply,Center postive- only turns on lights no signal sent
9v lithium battery- same result as wall warr
Anybody have any ideas other than powering it thru my laptop.