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I've built a custom Arduino shield using a PCB and surface mount components. The board has a short between power (5V) and ground (GND) when it is connected to an Arduino Due.

When the shield is not connected, the short does not appear to be present. With a continuity checker on my multimeter and the board disconnected from the Arduino, I've tested for continuity between GND and all the shield pins (including 5V). I only get continuity where I am supposed to - on the GND pins. I also tested for continuity between the 5V pins and the other shield pins (including GND), and only get continuity where I am supposed to - on the 5V pins.

How can I debug this problem? Why doesn't the shield show a short to ground when it is not connected, but when it is connected, there is a short? What am I missing?

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  • \$\begingroup\$ That's a tough one. Maybe the short is caused by pressure on the headers when the shield is connected. Well, it's just a wild guess. \$\endgroup\$
    – Ricardo
    Commented Dec 28, 2013 at 3:07
  • \$\begingroup\$ How exactly did you determine that there is a short to ground when Arduino is connected? \$\endgroup\$
    – AndrejaKo
    Commented Dec 28, 2013 at 3:07
  • \$\begingroup\$ It might be worth adding the schematic and layout of your board. Maybe it's just a simple pin mismatch you've missed, but are you sure something doesn't get physically shorted when you connect it to the top of a USB connector or similar? \$\endgroup\$
    – PeterJ
    Commented Dec 28, 2013 at 3:08
  • \$\begingroup\$ @PeterJ, That's a possibility. I had to insulate the top of the USB connector on my Arduino UNO with tape, just because of that. \$\endgroup\$
    – Ricardo
    Commented Dec 28, 2013 at 3:10
  • \$\begingroup\$ PeterJ - it was a pin mismatch as you suggested. \$\endgroup\$
    – Adam F
    Commented Dec 28, 2013 at 16:35

1 Answer 1

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I found the problem. It was a pin mismatch. The Eagle schematic was correct, but I had the shield XIO connector reversed in the Eagle board layout - so I had two pins connected to what I thought was ground, but on the Arduino Due, they were connected to +5V.

It's a 4-layer board. I found the problem by looking at the different layers in gerbv - when looking at the ground (GND) layer, I noticed there were two ground connections that shouldn't be there... that led me to discover the connector was placed backwards in the Eagle board file.

Here's a picture of part of the ground layer of the board that has the problem. The two pins in the upper right are +5V on the Arduino, but connected to ground on my board.

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  • \$\begingroup\$ "a pin mismatch" I hate those, +1 \$\endgroup\$
    – Wayfaring Stranger
    Commented Dec 28, 2013 at 18:05

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