That Final Check

I’m not talking about the final check that you get from an employer laying you off due to outsourcing. That’s a bummer of a final check. The final check I’m talking about is a good thing. It always pays to do this kind of final check. Of course the other kind of final check pays too, but only once. This kind can pay off numerous times.

Here’s the scenario: I have an MCU board that can take 5v power from either USB or from a dedicated power source. I want part of the board to receive power all the time and one small high-current section Schematic wrong pwr source to receive power only from the dedicated power source. I don’t want to suck too much current out of a poor little USB.

My circuit has three different power busses: USB regulated 5V, on board regulated 5V, on board 9-12V. I even fabbed up some PCBs and built a first prototype. It needed a few mod wires, but I missed this problem. After my mods shown on the older posts, the circuit still worked, so I stopped looking for problems.

Fortunately, I took one last look before sending off for v2 PCB. Two of my bypass caps went to the wrong supply (they were supposed to go the “BRD5V” instead of “5V”). Not a huge deal and in my test set-up, it didn’t prevent the circuit from working, but who knows what would have happened in real use. In any case, it would either resulted in another board spin or left the potential for intermittent problems when in use.

Duane Benson
Once again, time for oatmeal

5 thoughts on “That Final Check

  1. I’ve seen a similar instance where an engineer passed me a schematic that had nets: 5V-1 and 5V_1 on different sheets of the schematic that he intended to be connected together, unfortuneatly the 50k cad package the large global company was using didn’t have any ERC checking for this error.

    The 3K CAD package I use nowadays for a small/medium size company does, though it’s still a struggle sometimes to get Engineers to use it before they pass me the design!


    And wait until assembly installs a tant cap backwards on ya! 🙂 Regardless if the power signal name is right or wrong, FR4 material DOES NOT like backward tant caps…

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