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Boring bring-up pt. 1

A project log for Terrible Cluster

5 Raspberry PI Zeros. One custom USB hub. Endless disappointment.

ajlitt 09/14/2017 at 05:590 Comments

The boards came in today, so naturally I had to get soldering despite being tired from working late last night.


I populated everything but the USB power jack and the four downstream node USB plugs.  I didn't want to waste the connectors until I checked out the upstream end of the hub.

I first smoke tested the board with my bench PSU and checked that the oscillator was doing its thing.  Once satisfied that I didn't have any surprise dead shorts, I hooked it to my PC through a micro USB jack to USB-A plug cable going to an intermediate sacrificial hub.  I was able to see the hub enumerate under Linux, and checked that it's reporting as having per-port power control.


I also did a test fit of a Pi Zero W, and since I'm now confident it's not going to do any damage I powered it up.  The Pi's LED did its blinking thing as usual as Linux boots.

Stuff I learned:

  1.  The hole dimensions for the USB vertical plug are too big to fit snugly.  I had to "justify" the upstream plug with one edge of the board.  I'll need to remember to align the other four the same way to keep the Zeros spaced uniformly.
  2. The Cypress hub IC shuts off the 12MHz oscillator when nothing interesting is happening, probably to save power.  I didn't catch this detail in the datasheet.  I spent a good half hour wondering why I'd see a fleeting 12MHz on the scope on power-on and nothing afterwards.  I suspect it will stay on once I get downstream devices connected.
  3. My thermal reliefs aren't that relieving.  I soldered in one of the electrolytics backwards, and it was a pain to desolder and clean the hole on the grounded leg.  I should have used thinner spokes on the reliefs, and made sure that there was no additional ground traces hiding under the plane fill.  It would also help if I replaced the solder sucker I broke a few years ago.
  4. Just because silkscreen art looks good in the KiCAD 3d render doesn't mean it will look the same on a finished board.  For grins I converted a photo of a picture one of my kids drew in school to a KiCAD symbol.  What was supposed to be a skull looks more like an upside down diseased pear.  Elecrow and other PCB manufacturers have a resolution limit to their silkscreen.

Next I need to get the rest of the connectors in, test downstream power control, make up a test cable for the downstream ports (more later), and maybe plug in some more Zeros.  But that will have to wait for the weekend.

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