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Thoughts on Automation PCBs

I’ve been very satisfied with using custom Printed Circuit Boards to replace DIN rail break out boards and terminal blocks at work.  However, they aren’t always the best choice.

The advantages include:

  • Much reduced wiring time (especially when used with off the shelf cables).
  • Competitive BOM cost (possibly even less expensive; I haven’t run the numbers).
  • Reduced clutter.
  • Enormous component choice, including all kinds of connectors not available in DIN rail terminal blocks, along with semiconductors, resistors, jumper blocks, etc.
  • Affordable even for small volumes (I’d say starting at 3 boards)

The disadvantages include:

  • Not very flexible — once a PCB is made, it’s hard to change, unlike discrete wiring.  You can add a bit of flexibility by using a number of common PCBs instead of one big, custom PCB (e.g. for 3 axis system, use 1 PCB per axis instead of 1 PCB for 3; then if you need a fourth axis, it’s easy to add another PCB).
  • So PCBs are not a good match for unique machines, or ones that might radically change in unpredictable ways.
  • Using PCB design software takes some expertise and learning.  It’s not that hard (heck, I’ve done quite well using Eagle PCB, and I’m a software guy), but there’s definitely a somewhat scary learning curve both when designing the PCB and getting it manufactured.
    • Other software might be easier than Eagle PCB, especially software integrated with a specific board house.  But any general purpose PCB design software will have a learning curve, because it has to be able to handle so many design possibilities.
  • High voltage and high current take even more expertise.  You can do high current and high voltage on a PCB, but you’ll have to know even more about topics such as creep distances, trace widths, PCB copper amounts, board materials, and thermal dissipation to do it right.
    • So I wouldn’t be making a PCB for a 35kW 480V motor (although it could be done…)
  • Your favorite components might not play well.  One reason I use Panasonic PLCs instead of, say, Siemens’ intriguing S7-1200 is that I can easily make ribbon cables to go from the Panasonic PLC to a custom PCB, but I can’t for the S7-1200 (since it uses terminal blocks).

Another option is to have somebody else design and/or make a custom PCB for you (Wago is one possibility, and I’m sure there are others).  I doubt this approach makes sense for small volumes.  For example, I’ve done some research on getting our PCBs assembled, and prices I’ve seen at our volumes aren’t even close to reasonable.


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