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I'm using a breadboard to prototype my projects. On one pin of an MCU, which is an output, I'm getting a 0-3.3V signal, as expected. However, another pin has a 20mVp-p signal almost matching the other one, but lower in amplitude. Where is this coming from? Has my board got a weak short or something like that?

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  • \$\begingroup\$ Can you isolate that it is the breadboard? Like can you pull the 2nd pin out of the board and see if there is this same signal? \$\endgroup\$ – Kellenjb Nov 7 '10 at 22:39
  • \$\begingroup\$ The pin is set as an input, is there anything else I can do? it's going to be tricky to remove only one pin without damaging the MCU, and I only have one spare. \$\endgroup\$ – Thomas O Nov 7 '10 at 22:41
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    \$\begingroup\$ I have found DIP components very easy to just bend one lead and then bend it back. \$\endgroup\$ – Kellenjb Nov 7 '10 at 22:44
  • \$\begingroup\$ You can also change where the MCU is located on the bread board as well as take the MCU out and measure the resistance between the 2 rows. \$\endgroup\$ – Kellenjb Nov 7 '10 at 22:45
  • \$\begingroup\$ is that input just floating? if so, and you put a 10k to one of the rails, it should suppress some of the noise. \$\endgroup\$ – JustJeff Nov 7 '10 at 22:54
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The spikes you are seeing are just an effect of your breadboard allowing coupling. This is expected with any breadboard.

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    \$\begingroup\$ Capacitive coupling, in particular. \$\endgroup\$ – Connor Wolf Nov 8 '10 at 1:29
  • \$\begingroup\$ if a rising signal causes positive spikes, it is capacitive. It could be reverse traveling noise otherwise that is reflecting off of a low impedance driver. \$\endgroup\$ – Kortuk Nov 8 '10 at 1:38

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