lotus



previous page: 4.5.1) What's all this about problems with Macintosh Powerbooks and MIDI?
  
page up: Electronic and Computer Music FAQ
  
next page: 5.1) Is an overview of "General MIDI" available?

4.5.2) How can I build my own MIDI interface for the Macintosh?




Description

This article is from the Electronic and Computer Music FAQ, by Craig Latta Craig.Latta@NetJam.ORG with numerous contributions by others.

4.5.2) How can I build my own MIDI interface for the Macintosh?



From: henges@ingr.com. (John Hengesbach) Newsgroups: comp.sys.mac, rec.music.synth
Subject: Re: DIY MIDI interface?
Keywords: MIDI
Date: 30 Dec 88 16:05:21 GMT

In article <817@ttrdf.UUCP> fjo@ttrdf.UUCP (Frank Owen ) writes:
>
> Has anyone figured out how to kludge up a Do-It-Yourself MIDI interface
>for the Macintosh? It seems that the one Apple sells has practically no
A reply...

MINIMAL MAC--MIDI INTERFACE
===========================

Well, here it is all you MIDI fans. THE ultimate in
simplicity!! This is a simple schematic for a serial
to MIDI converter.

There are two functions performed here. One is the
conversion from current loop to RS-422. The second function
is supplying the 1 MHz signal for the serial chip to sync
up with the 31.5K baud rate of MIDI.

         >>>>>>> DATA FLOW >>> (MAC TO MIDI INSTRUMENT) >>>>>>>>>
               +-------+     +------+
To MAC   4   10|26LS32 |     |7407  |
Serial  >------+       |11  1|      |2    +------+    5
Port     5    9|       +-----+      +-----+R=220 +-----<  \
DB9 pin >-------       |     |      |     +------+         \  (5 pin DIN socket) Numbers        |       |     |      |                       | MIDI OUT
               +-------+     +------+                      / (to instrument)                 +------+                  +------+    4   /
      +5 volts -+R=390 +--+     +5 volts -+R=220 +-----<
                +------+  |               +------+
               +-------+  |  +------+1    +------+    4
         8    6|26LS31 |  |  |MCT2  +-----+R=220 +-----< \
        >------+       |11| 5|      |     +------+        \  (5 pin DIN socket)          9    5|       +--+--+      |                      | MIDI IN
        >-------       |    4|      |2                5   / (from instrument)                |       |   +-+      +------------------< /
               +-------+   | +------+
                           |
                           v
                           Ground
         <<<<<<<<<<<<< DATA FLOW << (MIDI INSTRUMENT TO MAC ) <<<
  
               +-------+     +------+
         7   10|26LS31 |     |1 MHZ |
        >------+       |9   8| OSC  |
         3   11|       +-----+      |
        >-------       |     |      |
               |       |     +      |
               +-------+     +------+
  
	Power connections:
  
	  		GROUND	+5
			-----	--
	  7407		7	14
	  26LS31	8,12	4,16
	  26LS32	8,12	4,16
	  OSCILLATOR	7	14

Notes:

The optical isolator MCT-2 above can probably be any relatively
fast optical coupler. Note that the 390 ohm resistormay need to be
adjusted to make sure the output does not saturate. Using a scope
while feeding a MIDI signal in should show you whether the signal
looks clean.

The diagram has been drawn to show MAC signals on the left
and MIDI signals on the right. There have also been allowances made
for the fact that 80 column ascii displays are not **exactly**
graphics terminals. Also note that the MAC pin numbers are for the
DB9 connector **NOT** the 8 pin mini-DIN connector!!

The age old question of where to get power for this always
remains. On the pre-MAC-PLUSs, there was power available from the
serial port connector. I solved this problem by finding a 7 VDC
AC adapter at a parts store and using a 5 volt voltage regulator
IC to bring it down to 5 volts. This is left as an exercise for
the student.....

The 26LS31 and 26LS32 are the same type of chips which are
used in the MAC for RS-42? conversion. I got them from a store in
Santa Clara California (Anchor Electronics (408) 727-3693). They
also have 1 Mhz Oscillators as well.

I have built several variations of this over the last two
years and have had good success using a variety of music software
with them.

John Hengesbach
(205)772-1669

uunet!ingr!henges
Intergraph Corporation
Huntsville, AL 35807

 

Continue to:













TOP
previous page: 4.5.1) What's all this about problems with Macintosh Powerbooks and MIDI?
  
page up: Electronic and Computer Music FAQ
  
next page: 5.1) Is an overview of "General MIDI" available?