  /* relay - to switch intercoms  */ (C)1994 Roger Howard. All Rights Reserved.
                                                                  ____________
               X------------------------------X                  |
               |   X--------------------------|-----------------X|>  intercom
               |   |                          |                  |   slave #1
               |   |                    X-----|-----------------X|>
               |   |    X---------X     |     |                  |____________
   --X---------X---X----X---|     |     |     |
     |         |   *\   |   |     |     |     |                ____________
     C         |      \o|   |     |     |     |               |
     O         |___*        |     X-----|-----|--------------X|<  intercom
     I          ____        |           |     |               |   MASTER
     L         |   *        |     X-----|-----|--------------X|<
     |         |      /o|   |     |     |     |               |____________
     |         |   */   |   |     |     |     |
   --X---------X---X----X---|     |     |     |
               |   |    X_________X     |     |                   ___________
               |   |                    |     |                  |
               |   X--------------------X     X-----------------X|>  intercom
               |                                                 |   slave #2
               X------------------------------------------------X|>
                                                                 |___________
*Remember to use a diode, color band to '+' (positive) voltage.
