
*******************************************************************************
*                      Amiga MIDI Interface Schematic
*                            by Steve Stevens
*                       c) 1986 all rights reserved
*                       Released into Public Domain
*
*******************************************************************************
Parts List for MIDI Interface:

    Qty.              Item
____________________________________________________________________________
   
    5             5 pin 180 degree DIN jack  (female)
    1             Male DB 25 connector  (plugs into serial port)
    1             8-pin  DIP socket   (for 6N138)
    1             14-pin  DIP socket   (for 74LS04)

    5             220 Ohm 1/4 watt resistors
    1             1k Ohm  1/4 watt resistor
    1             180 Ohm  1/4 watt resistor

    1             1N914 diode or equivalent
    1             75LS04  IC  Hex Inverter Buffer
    1             Hewlett Packard 6N138 opto-isolator  (or Sanyo PC 900 with
                      corresponding pinout changes)
    
    Misc.         wire, a box to put the stuff in, etc.


     All in all this project is pretty easy to put together.  Other computers
require a separate UART to make this sort of thing work.  But thanks to the
programmable UART already in the Amiga it becomes pretty easy.

     The schematic was drawn using Dpaint in hi-res mode so to view and print
the picture, you will have to load dpaint in hi-res mode by typing:

1> dpaint h
 
   from CLI.  Then load the picture MIDI.hires and print it out as you would
any other dpaint picture.  MIDI.hi.info must be renamed MIDI.hires.info.

     The shematic should be fairly self-explanatory for anyone with a little
electronics experience.  I hope it is.  
     I built the circuit on a small piece of perfboard and mounted it in a
black plastic box.  The hardest part was drilling the holes for the DIN jacks
to mount in.  I drilled a pilot hole with a regular drill and then enlarged
it with a rotary rasp that attached to my drill motor.  It made nice round
holes and was fairly quick.  The holes need to be 5/8 " in diameter.

     This circuit has all the features of any other commercial MIDI interface
available for the Amiga, plus two more out jacks.  These extra jacks are made
available for those folks with many keyboards (like me) who want to avoid
the mysterious and elusive MIDI delay problems.  With three OUT jacks you
also may not need a separate MIDI-thru box.  If you have only one synth that
you want to connect you may want to eliminate the other two jacks.  Just
don't hook them up and they won't be there.  Or, if you think you need one
more out jack you can hook up one more OUT jack by duplicating the out-jack
circuit and connecting it up to the sixth hex-inverter in the 74LS04.  I
didn't include it because I didn't need it.
     The one thing this interface doesn't have is a drum-sync port.  I don't
have a drum machine so I didn't need one.  If there is enough response I
will update the circuit with one.

     One more thing, a dot at an intersection point is the indication that
there is an actual connection.  When lines simply cross, there is no con-
nection.
     
     This circuit works fine for me and was easy to build but I will take no
responsibility nor will I be held liable for anything wierd happening with
someone else's computer.

     Altogether it cost about $8 in parts and a few hours of time to put
together.  That's alot less than the $50 one's in the store.

     I can be reached at    Amiga BBS  (303) 693-4735   Steve Stevens
                      or    People Link   ID# IGZ542    

GOOD LUCK !!!!!!!!!!!!!!!!
    









