RELAY Version 1.0
Copyright 1994 Roger Howard. All rights reserved. Feb. 4, 1994
  First some history. I wanted to switch a few things around the house.
  I wanted to do this from the computer with program control. After
  pricing the real switchers at several hundred dollars, I realized I had to
  do it myself. ( A fine excuse to have fun, says my wife.)

  The printer port is a parallel port. 8 bits wide at the output.
  After testing the port with LEDs to see if it would do what I needed,
  I built the 2 relay version, just to see it really work.
  You can get these parts for less then $20 at Radio Shack.

  Here are the plans to build yourself a nice relay switcher.
  These plans work for me.
            But you know I have to make this disclaimer statement......
                      CAUTION                  CAUTION
  I will not be liable for ANY damage (of ANY kind) resulting form the use of
  this hardware or the programs that came with it. If you build this, you will
  have to assume all risks.

                   !!!  USE AT YOUR OWN RISK.  !!!

  I have tested this on a real IBM PC-XT with mono monitor card
  using LPT#1 address of 03BC Hex and on a TI notebook (TM2000),with LCD-VGA.
  Also on an IBM PC-XT, and an XT-Clone.

Parts List:
   1   perfboard
   1   DB25 M  connector (male  -  with pins in it.)
   2   IN914 diodes
   2   2N2222 or 3904 NPN transistors  (I used 3904 from Radio Shack.)
   2   220 ohm resistors    (330 ohm or 470 ohm may work. 1K ohm was to big.)
   2   5 volt relays   (be sure to have contacts heavy enough for your load.)


                                                            _________
                                                           |         |X-- c
 5v D.C. from power supply                                 |         |X-- o
  <---------------------------------------X--------X------X|--\      |X-- n
                                          |     ___|___    |  / c    |    t
                                          |       / \      |  \ o    |X-- a
                         c ___           /      /_____\    |  / i    |X-- c
                     _____/   \         |          |       |  \ l    |X-- t
                    /   / \     \------------------X------X|--/      |    s
 pin #2          b | |/    |            |                  |_________|
  <----/\/\/\--X---|-|     |            |                     relay
       220 ohm     | |\    |             \
                    \___\*/               |
                          \_______x       |
                         e        |       |
                                  |       |                 _________
                                  |       |                |         |X--c
                                  |       |                |         |X--o
                                  |       |-------X-------X|--\      |X--n
                                 /             ___|___     |  / c    |   t
                         c _____|_____           / \       |  \ o    |X--a
                     _____/     |     \        /_____\     |  / i    |X--c
                    /   / \     |       \         |        |  \ l    |X--t
 pin #3          b | |/    |     \        \-------X-------X|--/      |   s
  <----/\/\/\--X---|-|     |     |                         |_________|
      220 ohm      | |\    |     |                            relay
                    \___\*/      |
                          \      |
                         e  \----X
                                 |
                                 |
 pin #18                         |
  <------------------------------X


                           Special Notes:

Pick 5 volts D.C. from power supply to feed the relays coils. Get this from
a red wire at the connector on the mother board
The diode has a colored band at one end.
This end MUST go to the  +5v D.C. end  of the relay coil.

The transistor's emitter goes to the DB-25 connector, pin #18. This is ground.
The transistor's collector goes to the relay coil and the diode.
The transistor's base gets the 220 ohm resistor.

The other end of the resistors go to pins on the DB-25 connector.
    Pin #2 for first relay.
    Pin #3 for second relay.

For a better drawing of this circut showing more detail send a
self-addressed-stamped #10 (business size) envelope with your request.

Special thanks to my friend Jim Hodges for encouraging me to get around to it.

P.S. Don't forget this is shareware, and isn't truly free.
       Please register your copy now. Send $10  to
         Roger Howard
         c/o BOX # 16371
         Baltimore, Md. 21210

         HAVE FUN !!!!
