How to build a Windows midi interface for little money.

This project consists of 2 basic items.

1) software
The software is a windows  driver which will send and receive midi data from
and to a COM port. Read the .WRI file in the UNIVDRV.ZIP.

2) Hardware
The hardware is a standard serial card  which is provided with a midi signal
interface. The trick is to exchange the RS232 drivers with a midi-interface.
SER_MIDI.GIF  contains a schematic  on how to  do this  which I will explain
below.

Schematic.
Top left  you can find the midi  input. A 6N136  optocoupler will make a TTL
compatible  signal. This  signal is fed  into Q1 and  the UART (8250). Q1 is
the driver for the THRU output. All midi data entered into J3 will be echoed
to J1. In the middle you can find the  output  circuit. Q2 is  used to drive
the output.

Oscillator.
The goal is to clock the UART with a 1.5MHz signal. There are two options to
achieve this.
1) Normally  the UART  in a PC is always clocked with a 1.8xxMHz signal. You
   can  alter  the  clock  frequency  by  changing the crystal. If there's a
   18.xx MHz crystal, replace it with a 15MHz one, etc.
2) I had a dual-channel board (=two serial I/O ports on one  card). I wanted
   to use one  channel as a normal RS232 interface and one as MIDI. I choose
   to make an extra oscillator. The  oscillator circuit is also shown in the
   schematic.  Of  course  the  clock  pin  of  the  MIDI  UART  has  to  be 
   disconnected from the original clock source.

For question etc, email me at:

nctnico@cistron.nl