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This is a short post so that I can collect my thoughts on my recent experience with the Othermill.

I’m starting to test the firmware for the Ladybug Blue Lite.  The Ladybug Blue Lite is an expansion to the Ladybug offering.  The Ladybug Blue Lite differs from the Ladybug Shield in the following ways:

  • the Arduino and BLE shield are replaced with the nRF51822.  Instead of stackable shields there is one PCB.
  • it does not adjust pumps.  It only updates pH and EC readings.  I found many instances where I just wanted the pH and EC.
  • it runs on a LiPo battery.  I wanted to be able to put the Ladybug Blue Lite around my outside garden.

My goal is to get to reading a pH value and then an EC value using the same circuitry I am designing within the Kicad schematic.  In order to reach the first goal of getting a pH reading, I built a PCB using my Othermill.

OthermillpHBoB

Areas where my skills at using the Othermill have evolved after this effort:

  • I clear off non-copper areas.  I found that when I did not do this I would get shorts.  I used the technique I discussed in this post.
  • while the pitch between the pins of the MCP6242 requires a 1/100” mill, longer tracks should be at least 40 mils.  It was too easy for the track to get an opening when smaller.
  • Use a spacing of 5.08mm (twice 2.54mm header board spacing) when using headers.  This way, the headers can have more copper around the hole.  It is all too easy to burn off the copper when the copper around the hole is small.  Besides, it is difficult to cleanly mill and have enough copper at the 2.54mm spacing.
PadSizeForOthermillHeaders
  • I found using a hotter setting (say 350˚C) on the reflow gun and solder and lightly touching the solder was a better technique than soldering at a lower temperature. The less time putting heat on the copper the better chance I was having with the copper strips not coming off.
  • Ugh.  Still challenged by the name extension for the Gerber outline file.  Kicad creates a file with a .gbr extension.  I keep forgetting to change the extension to .gko.  I use an Automator script to rename..however I’m not having much luck getting the script to change the extension name (even though after Googling how to do this it should be ….grrrr…ummm…obvious).

Areas where I am left wondering:

  • Using the 1/100” mill – even though I used a 1/8” and then a 1/32” prior – takes a very long time.  A lot of what gets milled are small areas that don’t need to be.  I wish Otherplan allowed me to “cut out” those areas that don’t need the 1/100” mill.  For example, in this case the 1/100” mill was only needed to cut out the copper between the pins of the MCP6242.
  • At some point “soon” I should get high(er) quality mills in the sizes that make the most sense for making this type of PCB.  I’m thinking most likely a 1/8”, 1/32” and 1/100”.  Right now the UI of the Otherplan supports 3 mills on a project.  I believe there is a way to get into the files and add more.  Perhaps that’s something I should look into.  I’d like to minimize the 1/100” by adding a 1/64”.
  • I wonder if there is FR-1 boards that have a “better” copper layer such that it is more difficult for the copper tracks to get pulled up.
  • I wonder if there is a spray that I could apply to the board so that there is a protective layer above the copper as there is on the PCBs I get from OSH Park.

 

That’s it for now…on to seeing if the prototype works!

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