At 10:31 PM 3/6/2004 -0700, you wrote:
>Just wonderin what the 3rd pin on a typical power barrel connector is
>typically used for? This is the pin that connects to the center pin when
>there's no plug and it's not connected when there's a plug.

It's designed to switch between an internal battery and an external AC
adapter.

>In the past I've just left it NC, but I wonder if it should be used to
>ground the + input to the power supply.  There's a 7805 and a couple of 2200
>uF caps on this line.

It's generally bad practice to short the input of a regulator to ground,
though you'd get away with it in this case (but not with a 7812).

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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