I have a set up like this:
The PWM signals do not exceed 5V. The configuration to the right of the dotted blue line cannot change. Note that the external power supply is intended to power the input device only, and the ground is tied to the Arduino's ground.
When the Arduino is attached to the computer (and powered) by USB, everything works great.
However, I also need to be able to run the input device independently without the Arduino and a computer. The problem is, when the Arduino is not powered (e.g. USB disconnected) but the device is, the device's PWM outputs partially power the Arduino. There are two effects:
- Some of the LEDs on the Arduino dimly light, although it does not actually power on completely. This doesn't bother me.
- More importantly, it draws enough current from the input device to noticeably affect the device's operation. This is the problem.
Is there a way to prevent the Arduino from drawing current from the input device when the device is powered but the Arduino is not? I need the device to operate correctly regardless of whether or not the Arduino is running.