Noise with USB connection and power from power pack

Hi,

I have a USB MIDI foot controller project I am hoping to run from a Rockboard Power LT XL - this is a small rechargeable power pack primarily designed for powering guitar FX pedals, but also has a 5V 1A USB output; my project will be on a guitar pedalboard so this setup would work well for power.

Having finally finished wiring the project I plugged it in and was getting a high pitch noise on the guitar audio signal (note: no audio actually goes in to the arduino foot controller). With a series of trial and error I discovered the following:

  • Power from power pack to foot controller and pedals, USB plugged in to laptop = Noise
  • Power from power pack to foot controller only, USB plugged in to laptop = Noise
  • Power from power pack to foot controller and pedals, USB NOT plugged in to laptop = No Noise
  • Power to foot controller from seperate 5V USB adapter, pedals from powerpack, USB to laptop = No Noise

From this, I am concluding that the USB connection to the laptop is causing the issue; if it were a problem with the powerpack transmitting noise from the foot controller to the FX pedals then it would still happen whether the USB is connected to the laptop or not (I think? Correct me if I am wrong).

All grounds for input power, USB and everything else internal are common and I've gone round with a multimeter to confirm this.

Does it make sense that the USB connection is causing the issue? As I am not drawing power from the laptop USB port, would a USB isolator 'fix' this issue? Or maybe it is the powerpack?

speed12: Does it make sense that the USB connection is causing the issue?

Yes, computers are very noisy. :grinning:

speed12: As I am not drawing power from the laptop USB port, would a USB isolator 'fix' this issue?

Quite possibly. :sunglasses: Not guaranteed but very plausible.