   LPT Port
  does anyone know how to output data for controlling an electronic circuit to the printer port? 
  I''m assuming you mean under Win32?  You need a driver for it - there''s a generic one out there, but I don''t recall what it''s called or who made it etc... ;  Win32 supports LPT communication in a fairly straightforward manner. The documentation on CreateFile has some of the details. 