PocketBeagle power decoupling of the USB busses

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1

Dear all,

I am not completely sure where my problem is but I think I have narrowed it down to its core and it seems to be a power (stability) issue. Solving it might be a hassle but maybe you can help.

I have a 3Dtouch sensor from microchip: https://www.microchip.com/DevelopmentTools/ProductDetails/DM160225
And I also have a Wifi USB dongle from Edimax: https://www.edimax.com/edimax/merchandise/merchandise_detail/data/edimax/global/wireless_adapters_ac1200_dual-band/ew-7822ulc/

Both are connected through USB to the beaglebone, the 3Dtouch on bus 002 (the USB bus on the pins) and one on bus 001 (the micro USB OTG connection) using a micro USB to USB A female adapter.

The board is powered with a duo cell LiPo using a step down regulator from Pololu (5V, 5A) on Vin and VB and Vin-USB (pin 1-1, 1-5, 1-7).

Sensordata from the 3Dtouch gets distorted by the Wifi dongle and I suspect that interference on the power bus is the cause of it since a stronger power regulator does help somewhat in stabilizing the issue. Furthermore using a USB extension cable on the USB wifi dongle reduces the problem substantially. Such a cable on my project would aesthetically and practically not be preferred though. From the schematic of the board I see that USB1 and the micro USB are connected with a ferrite bead (FB1).

  1. Would it be an option to remove FB1 and power USB1 separately from the microUSB?
  2. Would it be possible then to power the USB bus 002 with the sensor board on pin 1-5 and 1-7 and the rest of the board including the micro USB bus 001 through V1-1 with a separate power supply (separate power regulator)?
  3. Should I also do something with Vbat?

And of course would that probably solve my problem? Or does someone else recognize my issue and has a better solution?

Thanks for paying attention.

Best, Hans.

2

Sorry I said beagleBone, but it is pocketBeagle of course. Essential difference for this question.

3

Dear all,

The problem is solved as far as it can be solved. It is not a power stability issue as I thought it was although it was not far from it. The specific microchip sensor itself needs grounding when it is used in a battery powered situation. Unfortunately that was not in the datasheet of the sensor that I used but it was found in a similar device’s design guide: http://ww1.microchip.com/downloads/en/DeviceDoc/40001716C.pdf (page 23 if you are interested). Luckily the sensor will be used in the proximity of a decent amount of brass (trumpet) so my problem is more or less solved.

Thanks for paying attention if you did.

Best, Hans.