MIDI question

[Bob Eldred]

Hello, Bob.

The main reason why I will be building my own opto-isolator, rather
than sending away for one, is because I would rather not wait for
shipping. You have said that the isolator has to operate on five
milliamps. Can you give me a reference for this? I will build a
driver, if I need to. I still don't see any problem. The Sharp 6N138
doesn't seem to have the right parameters. According to Digikey, it is
supposed to operate on one-and-one-half volts. And none of the 6N138's
that I have seen have a Schmitt trigger. Mine should be faster.

Where do you live that shipping is an issue? As one poster said, your going
to need a lot of information about MIDI to be successful. A good starting
point is the book, The MIDI Manual by Huber published by Sams. The five
milliamp current loop is discussed in there and is in the MIDI spec. If you
don't design to that no other MIDI device will be able to talk to you, not a
good start. Also go to the MIDI web site, I don't have the URL, and down
load information and specs. It's very useful. Yes, the 6N138 is not a
schmitt trigger device, just a darington but it does have the current and
speed required. If you use it be sure to bypass the second base with a 10K
resistor to ground or it won't be fast enough. There is a lot to MIDI and
you will need to have some way of processing the information, a micro
processor or something. What is you plan? Actually the opto-isolator, though
required, is almost incidental and is childs play compared to other MIDI
issues, as you will find out. Good luck.
Bob

 

[MikeMandaville]

Bob, if you're still there, I'm sorry that it's taken me three days to
respond. I know that I've been a bit of a pest about this, but I'm
happy to report that I now have succeeded in cross referencing the
Sharp PC-900 opto-isolator which is illustrated in the MIDI electrical
specification to the Fairchild H11L1M. I'm sure that the 6N138 would
work just fine, but since the H11L1M seems to be just what I was
looking for, I've decided to go ahead and use it.

I appreciate you explaining about the five milliamp current
requirement, and, after locating my MIDI reference, "The Musician's
Guide to MIDI", I have noticed that the author, Braut, does indeed make
mention of this himself.

By the way, what I have in mind is something which is probably
relatively simple - at least, compared to what it might have been. I
will be building a portable MIDI file storage box, which I will use to
download files from my computer. I will then use the box as a music
keyboard controller. The idea is to save me from lugging my desktop
computer around.

Thanks for the help, guys, and I'll keep you posted on my progress.
Mike "Chip Monk" Mandaville