[sdiy] Optoisolator for MIDI

[R. D. Davis]

While looking over various circuits for a MIDI interface that connects
to a PC's sound card, I see that most of them use the 6N138
optoisolator.  A few of the earlier schematics that I've seen used a
4N35 optoisolator; does anyone see any problems with still using the
4N35 (along with appropriate resistors values, etc.)?  Also, any
problems with using a 4N35 in a MIDI ckt for an older Power Mac's
serial port?  I'm planning on building ckts for both the PC and Mac.

If I get these to work, perhaps I'll then go for adding MIDI to a Sun
workstation serial port, my PDP-11/73 and VAX ...might turn out to be
useful for something or other, so why not?  It would be fun to try out
John Wilson's (IIRC) circuit for a PDP-11 MIDI interface. :-)

Also, I read somewhere that some of the newer sound cards won't work
properly with some of the circuits used with the old Soundblaster
cards, and that one has to add either an IC buffer or a transistor
ckt.  between the sound card and the optoisolator; seems to me that
newer cards would require less, not more, current, however.  

Any thoughts or advice on this?

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