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• Testing on a Raspberry Pi 3B+

  Kyle Isom • 08/02/2019 at 03:56 • 0 comments

  It mostly works. Building ROS packages causes it to power off, which I suspect is due to not being able to source enough current.

• V2 testing results

  Kyle Isom • 08/01/2019 at 04:53 • 0 comments

  I hooked up some power resistors (1-8R 10W) to the various outputs and ran it through its paces.

  First up was supplying 8V @ 1A to an 8R resistor hooked up to the motor controller (8V / 8R should be roughly 1A). 

  Next, I attached a 4.5R load to the 3.3V output (2x1R in parallel with a 4R in series). The LM111733V is limited to 800mA sources, so that should give 733mA that's around 2.5W. After about 30s, it starts to short circuit; I suspect this is due either to the traces not being able to supply the current or the resistors overheating and causing problems; at 10W, I wouldn't suspect that but they did feel pretty warm afterwards.

  Finally, I tried supplying 8V @ 1.1A with 4.5R load on the 5V outputs (which should be about 1.1A). There's a 0.2V drop across the load, which I suspect is due to the load.

  I did try switching the motor kill switch while the load was applied and it didn't fuse, which is a good sign.

  The tests indicate that I should aim for improved thermal dissipation and widen up my traces.

• v3 / v4 prototypes

  Kyle Isom • 07/31/2019 at 19:00 • 0 comments

  I wasn't happy with the parts I'd used in Eagle and the resulting silkscreen, so I updated the board... which meant having to rearrange things. So that's v3. I also added some indicator LEDs to a v4 board with SMD parts; I'm keeping v3 and v4 separate so as to keep the option of not doing SMD open.

  Something that I've been thinking about is whether the copper trace widths I used (10 mil) is enough for the power I want to pull. I think the traces are short enough that it's fine, but think v5 is going to feature wider traces.
  

• Prototype arrived

  Kyle Isom • 07/31/2019 at 01:07 • 0 comments

  The prototypes arrived! I hastily assembled one to test it...

  The capacitor footprints are a little small, so I'm going to have to update the board to fix that. I think I'll add LED indicators, too.

  It's testing working, though only under a bench power supply and not under load.

• Rev 2.0 assigned to panel

  Kyle Isom • 07/23/2019 at 23:45 • 0 comments

  Just got the email from OSHPark that the boards have been panelized - they should be sent to the fab in the next couple days.

• First boards ordered

  Kyle Isom • 07/23/2019 at 04:38 • 0 comments

  I ordered the first set of boards from OSHPark - we'll see how they turn out. I'm a little concerned that the power switch is only rated for 200mA...

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