2019-07-30

I have been playing with the latest revision of the VPSB (Vic’s Power and Serial Board).  I was hoping that this would be the last revision, unfortunately the fact that I crewed up the power supply footprint will prevent that from happening.  I got the pin order backwards.

This is the worst kind of failure since I can’t blame anyone else.  Anyways, here’s the potato-cam picture:

You can see the power supplies in the lower left all catawampus.  One of the side affects of the power supplies being installed backwards is that doing so fried all sorts of good stuff on the board.  That little screw up took out: the 3.3V reference, the PWM driver IC, current monitoring IC, and I suspect it damaged the PHI IC on the BeagleBone.

The good news is that it basically works.  All the serial port stuff works, the PWM drive kind of works.  Things are getting enabled and disabled as they should.

The software side is coming along nicely as well.  I simplified the current monitoring a lot.  It’s now purely there for informational purposes.  Initially I had the idea of sampling the current draw during the on portion of the PWM duty cycle, but that got to be a giant pain in the butt almost immediately.

So one more revision.  Hopefully this will be the final one.  One of the major changes in this revision will be the addition of capacitance on the output side of the 5V power supply.  It works 99% as is right now, but I think it can be better.  If I’m not careful I can cause the whole pile to reboot during startup as the 5V voltage takes takes a dip.