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Prototyping Is Good

I like automation software because the end result is visible, not just “in the cloud” with no clear connection to anything physical.  Furthermore, I’ve found it’s very good to experiment and prototype first; I do not rely on virtual designs (living only in CAD software on a computer) to be 100% correct.  Even if we had and knew how to use expensive simulation software, it’s still not real.  Toyota, which does make extensive and valuable use of simulations, is moving back to make more physical prototypes and do more testing with those prototypes.

First, it’s hard to get all the details right.   After I assembled my CO-DB9-RJ45-2 adapter board, I plugged it into a AMC DX15 servo drive and then I finally realized: oh, no, the power plug is on the wrong side and will hit the next connector!  (BTW, the simple solution is to use a fixed terminal block instead of a header and plug).

Second, there’s no substitute for actually trying to use, first, the components, and second, the whole machine.  You can’t simulate the feel of quality components.  And there are lots of little things that can bite you later.  That’s why I now prefer to get samples of connectors I’m interested in before using them on a PCB.

I really like the concept of IDC (insulation displacement) terminal blocks: all you have to do is insert the wire and clamp down.  There’s no wire stripping, no ferrules to crimp, and no screws.  So I used a lot of Phoenix IDC terminal blocks in one of my first PCBs.  They worked great for many wires, but one set had problems: one component had wires with really thick insulation (for no good reason IMNSHO), so we really had to cram the wires in, which isn’t a good thing.

So while I still like IDC connectors, such as the eCon style connectors (3M MiniClamp, Tyco RITS) I only use them when I know what the wire gauge and insulation diameter will be.

I’ve also started using a lot of spring clamp connectors.  They can handle a much wider range of wire (and insulation) sizes than IDC, but can still be quicker to assemble than screw clamps.  However, they have their quirks, too:

  1. I have a bunch of used early Wago DIN rail spring clamp terminal blocks which are significantly harder to use than the newer models.
  2. Large spring clamps can take a lot of force.  I realized that when using some 4.0mm 32A Phoenix DIN Rail spring clamp terminal blocks.  I’m not sure I’d want to use anything larger.
  3. It can be hard to get the wires into a spring cage plug: it takes one hand to hold it, one hand to operate the screw driver, and one hand to insert the wire — but I only have two hands.  When the plug is in its header, it’s easy to operate.

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