Computing stuff tied to the physical world

Good news and bad news

In Hardware on May 26, 2010 at 00:01

You’re supposed to tell the bad news first, so…

The Carrier Board described a few days ago works nicely, along with the box, Carrier Card, and EtherCard.

BUT… I completely goofed with the optional DC power jack connector :(

With the current board, the center pin is connected to ground. Whoops! I’ve hacked it for now by rewiring stuff a bit, and leaving 2 of the 4 solder pads on the power jack unsoldered:

Dsc 1475

If you look very closely, you’ll see some black electrical isolation tape between the board and this side of the power jack. The other side of the jack looks like this:

Dsc 1476

Warning – the wires are not attached correctly in this picture. The PWR line on the top side needs to be hooked up to the rightmost pin on the DC power jack.

It all looks worse than it actually is, because the whole thing gets mounted into a box and is also held into place by the cutout in the outer wall. So the power jack can’t really move around, despite the fact that it’s only held by two solder joints on a single side.

Oh well – s…tuff happens.

And the good news is…

There are actually two much simpler and stronger workarounds for this problem, because only a single copper pad is causing the problem. The copper pad in the very corner of the board is the only one that needs to be fixed!

The first workaround is to cut the two thin traces connecting this pad with the surrounding ground plane:

Dsc 1483

Since the traces are right next to the edge of the board and very thin, all you need is a Stanley knife to cut those two traces. A V-type cut is the way to do it:

Dsc 1482

Use a multimeter or continuity tester to verify that the pad is indeed no longer connected to ground.

Voilá! Now that the corner pad has been isolated, the power jack can be soldered on in the normal way, and wired into the rest of the circuit as needed.

The second workaround is to cut the pin off from the jack itself, so it can’t touch the exposed corner pad:

Dsc 1481

Better safe than sorry, so it’s probably best to also use insulating tape, as was done above.

IOW, the incorrect power jack connection is a major glitch, but there are several effective ways to work around it. Given that not everyone will even want that DC power jack option, I’m going to stick with these PCBs.

  1. Ooopsie…

    I applaud your public honesty.

    We’ve all been there, done that, blown the fuse (several times), blown the capacitors off the board and then done that again because it was so much fun!

    Given the number of wires on that board, if that is the only mistake I think you can congratulate yourself.

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