Here is a schematic of a lightpen that is reported to work reasonably
well with the vectrex. This is NOT the official vectrex lightpen.
Provided by Tony Duell <ard@p850ug1.demon.co.uk> April 1995


     +--------------------------+--------------------------+----- +5v (7)
     |                          |                          |
     /                          /                         === 4u7
     \  10k                     \ 2k2        4            --- (Tant)
     /                     10k  /          +---|\   6      |
     \                   +-/\/- +----------+   |#)o---+   -+-
     |                   |      /          +---|/     |   ///
     |        | |        |   |/              5        |
     +------- | | -------+---|    2N3904     74LS132  +-------- SW7 (4)
     |        | |            |\             (+5v=14, Gnd=7)     Output
     /        10nF             >\
  |/   MEL12                     |
  |\>  Photodarlington           |                       +------- Gnd (8)
    >\                          -+-                      |
     |                          ///                     -+-
    -+-                                                 ///
    ///

Notes
------
0) Not the official Vectrex lightpen.
1) Pin connections to vectrex left joystick port shown in brackets
2) For some reason, 74LS14 does _not work_ in this circuit. 74LS13 should be OK
3) MEL12 available from Maplin. Do not know of any equivlents
4) Use Seqa extension cable (with plug cut off) to make connection to vectrex.