Depends if "Wiegand card readers" is referring to the "real" Wiegand 
wire technology or to the interface of the same name, which is 
technically unrelated:

It appears it's the former from your description. This only provides a 
foot in the door, but ...
_____________


Wiegand wire, basic principle

        http://en.wikipedia.org/wiki/Wiegand_wire

Wiegand effect

    http://en.wikipedia.org/wiki/Wiegand_effect

_______________________________


Wiegand interface and protocol which is *NOT* directly related to the 
above technology but may be used with it

        http://en.wikipedia.org/wiki/Wiegand_protocol

        http://en.wikipedia.org/wiki/Wiegand_interface

Roll yer own PIC controller

        http://www.remember.ro/scripts/wiegand.php

Interface definition

        http://www.remember.ro/dl/wiegand/wiegand.pdf




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