Cheap MIDI

The following text explains how to build a MIDI interface for the
Sound Blaster. The circuit is my own design, but works just like
the commercialy available interfaces that retails for $60-$90.

Here is the list of parts necessary:

Qty.           Part

 1    Sharp PC900 or HP 6N138 opto-isolator
 1    DB15P (15 pin 'D' connector, male. like joystick connector)

 3    220 ohm resistors (2 for input, 1 for EACH output you need)
 1    3 conductor shielded cable (length is up to you)
 2    Female 5 pin DIN connector (1 for input, 1 for each output you need)
 1    PC board with pre-drilled holes (about 2" x 2" from Radio Shack)
      A few short lengths of hook-up wire

All of these parts, except the first 2, are available from Radio Shack.

Construction techniques are completely up to you, if you want to go
ultra-cheap, you don't even need a PC board or enclosure, and you could
use a MIDI cable you already have by cutting it in the middle. I used
a PC900 out of a non-working organ and cut the end off of a joystick I
didn't need and built the whole thing for about $4.00. Buying all the
parts new, and using an enclosure with built-in MIDI jacks may cost
about $20 or so.

Here is a diagram of the DB15P connector (looking at the solder side).

    1       5     8
    o o o o o o o o
     o o o o o o o
     9     12     15

Here is the 5 pin FEMALE DIN plug (solder side).

       2
   5   o   4
     o   o
  3  o   o  1


This is the circuit for the MIDI INPUT.


                                     +-----> To pin 5 of 'D' connector
                                     |
To pin 15 of 'D' connector <---+     |     +-------+-----> To pin 9 of 'D' con.
                               |     |     |       |
                               | 6   |5    |4      \
                             +---------------+     /  220 ohm
                             |     PC900     |     \  resistor
                             |      or       |     /
                             |   HP 6N138    |     |
                             +---------------+     +------> To pin 6 of PC 900
                               |1    |2    |3
                               |     |     |
                               \     |     +----->  No connection
                       220 ohm /     |
                      resistor \     |
                               /     +-----> To pin 5 of DIN connector
                               |
To pin 4 of DIN connector <----+


Don't overlook the two 220 ohm resistors.

Also, for cables longer than a few feet, connect pin 2 of the DIN to pin
5 of the 'D' connector.


The output circuit is much simpler.

                                  220 ohm resistor
To pin 12 of 'D' connector <---------/\/\/\/\/---------> To pin 5 of DIN con.

To pin 15 of 'D' connector <---------------------------> To pin 4 of DIN con.

Also, for cables longer than a few feet, connect pin 2 of the DIN to pin
5 of the 'D' connector.


This circuit has been built and tested by me, using Voyetra's SPJr, and
a cheap-o Casio keyboard. The input and output do work as shown here, but I
don't have any other MIDI devices to use to test using more than 1 output
device. Theoretically, it should work fine, but it has not been tested.
The chances of hurting anything by trying is slim and none.

This circuit DOES work, but I make no guarantees, nor will I be
held responsible for any damages you may cause from your use of
this information.

If you have any questions, or would like to buy one already built for you,
I can be contacted on:

The Lighthouse BBS (207) 255-3700   (username is Ronald Davis)
The Music Studio BBS (708) 351-0288 (username is Volstagg)