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Andrew,

The 7805 is a voltage regulator.  I use them all the time.  Because you're
seeing the led light (even briefly), it _sounds_like_ you're not connecting
the 7805 correctly.

Assuming you have a package that looks like this:


***********
*   (  )  *
***********
*   7805  *
*         *
*         *
*         *
***********
 *  *  *
 *  *  *
 *  *  *
 *  *  *
 1  2  3


with the IC numbers (and body of the package facing you), Pin 1 goes to +12
(or without getting too detailed, whatever the inbound voltage is.  Pin 2
goes to GND or COMMON and pin 3 is the regulated 5v output.  Bursting into
flames is not one of the chips features!

Hope this helps.

-Ed McCauley
Lancair IV-P -13.8%
Milford, NJ

LML website:   http://www.olsusa.com/Users/Mkaye/maillist.html
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Please send your photos and drawings to marvkaye@olsusa.com.