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Today I noticed that my Arduino board only has two of the pins of the voltage regulator hooked up. I thought I understood how it worked, but I must be missing something.

Why isn't the middle pin hooked up to anything? Was it always like this or did I break it? The board seems to work just fine.

enter image description here

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up vote 9 down vote accepted

The soldered tab on the regulator chip usually connects to the middle pin and you can bet half a years wage on IT being connected to the circuit: -

enter image description here

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Yes, you are absolutely right. I had thought it was just a heatsink, but it is soldered to the board too. Thanks. – kmort Jan 30 '14 at 4:32

There is a large tab on the other end of the regulator that is soldered to ground, and almost certainly also connected to the center pin.

From the board layout, I suspect that the regualtor is available both with and without the center pin, since there is a pad where the center pin would be soldered if it was on the package.

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It's not connected to ground - it's the output pin on an L1117 regulator. – Andy aka Jan 29 '14 at 22:27
@Andyaka: I was thinking of the 78xx series, where the tab is ground - I should have just said "soldered to the board"... – Peter Bennett Jan 29 '14 at 23:34
Okay, I see that now. Thanks a bunch. I just thought the big tab at the top was a heat sink before. – kmort Jan 30 '14 at 1:37

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