MIDI question

  • Thread starter MikeMandaville@aol.com
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MikeMandaville@aol.com

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Hello. I'm building a MIDI interface...

http://www.midi.org/about-midi/electrical.shtml

....and I'm planning on using off-the-shelf Radio Shack components to
build my own opto-isolator. Does anyone know of any reason why I
should not?
 
"MikeMandaville@aol.com" wrote:
Hello. I'm building a MIDI interface...

http://www.midi.org/about-midi/electrical.shtml

...and I'm planning on using off-the-shelf Radio Shack components to
build my own opto-isolator. Does anyone know of any reason why I
should not?
Click to expand...
You will certainly learn more by creating your own parts.
But what you learn may be that you should have bought the specified
parts,
to start with. ;-)

What Radio Shack components do you intend to try as substitutes?
You can make a pretty fair opto isolator with the emitter and detector
pair from an old mouse. Getting them well coupled is half the battle.

--
John Popelish
 
<MikeMandaville@aol.com> wrote in message
news:1104888479.412702.14490@f14g2000cwb.googlegroups.com...
Hello. I'm building a MIDI interface...

http://www.midi.org/about-midi/electrical.shtml

...and I'm planning on using off-the-shelf Radio Shack components to
build my own opto-isolator. Does anyone know of any reason why I
should not?

Why would you do that? Radioshack sell a perfectly adequate TLP620, which
Click to expand...
will at least have known characteristics. Unless of course the object of
your exercise is to learn about making optocouplers rather than MIDI
systems.....

Cheers.

Ken
 
See
http://haskey.com/johnh/organ/organ.html

I built that MIDI pipe organ about 15 years ago. I used 6N137s for the
isolators. I guarantee you'll have your hands full sorting out all the
MIDI stuff without having to putz around with possible faults from a
poor opto-isolator
GG
 
But in reading the original post, I just assumed he was talking not
of building an opto-isolator, but in using whatever Radio Shack still
stocked rather than tracking down the one that was commonly specified.
Click to expand...
The reason the 6N138 was commonly preferred was that the
cheaper alternatives were too slow to do MIDI. If you make
your own, make sure it's fast enough.
 
Hello again, fellows.

John, the specified parts are no longer available. Radio Shack sells a
"Matched Infrared Emitter and Phototransistor Detector" pair for $3.29,
Catalog #: 276-142, and this is what I will be using. I found out
firsthand about the IR pairs in my mouse about a year ago, when I
dropped my mouse one too many times, and it finally broke. When I
opened it up, to see if I could fix it, and I found two IR pairs, one
for each axis. I never did fix that mouse, so I still have those
components, and the main advantage I see in using them would be that
the LED's are so tiny that there seems to be little doubt that I could
drive them from my computer's JOYSTICK/MIDI port, which is where my box
will be hooked up. The reason why I have decided to work with the
larger components is simply because they will be easier to handle. :)
 
Hello, Ken.

Radio Shack no longer sells the TLP620
 
Hello, Michael.

Ken was right in the sense that I am planning on building my own
opto-isolator. Forrest Mims shows how to do this in his "Engineer's
Mini-Notebook" entitled "Optoelectronics Circuits", which is no longer
available. Mims suggests using heat shrink tubing, though I myself
prefer several layers of electrical tape. I've made dozens of them
before, and they always worked just fine.
 
Hello, Glenn.

I confess to being awestruck by your organ project. I have thought
about doing something similar myself, though I don't yet have the
resources. I've had my music keyboard hooked up to my computer for
about two weeks now, which is nice, because now when I play midi files,
I use my computer as a music keyboard controller, and since my music
keyboard is also hooked up to a little ten watt amplifier, I get a
better sound than I used to when using my computer speakers. Even so,
there is nothing like the sound of a genuine acoustical instrument, and
your organ is really beautiful.
 
On 5 Jan 2005 12:20:23 -0800, the renowned "MikeMandaville@aol.com"
<MikeMandaville@aol.com> wrote:

Hello, Ken.

Radio Shack no longer sells the TLP620
Click to expand...
You can get a 6N138 from Mouser or Digikey for < $1.00 one-off.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
Hello, Clifford.

Though there is little doubt in my mind that I could probably drive my
homebrewed opto-isolator to more than twenty times the bits-per-second
speed which is required by the MIDI specification, an opto-isolator is,
of course, an analog device, and so it will be necessary for me to
convert its analog output into a digital signal before that signal will
then be "fast enough" for me to be able use it. Evidently, the Sharp
PC-900 opto-isolator which is in the MIDI specification had its own
on-chip Schmitt trigger to accomplish this purpose. The Schmitt
trigger is a simple circuit which I will be able to build from locally
purchased discrete components, and so there is no reason why my
homebrewed opto-isolator should not be just as good as the one which is
shown in the specification.
 
"MikeMandaville@aol.com" wrote:
Hello, Ken.

Radio Shack no longer sells the TLP620
Click to expand...
Digikey still has them for $0.72.

There are also many other units they sell that are equal or better.
--
John Popelish
 
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.
 
Rich Grise (richgrise@example.net) writes:

If you have a budget of $25.00 or more, you can get practically anything
you need from Mouser, http://www.mouser.com . If you have a DBA, you can
go request information from http://www.newark.com and a salesman will
call, and open a credit account for you. ;-)

If I was building one, I'd use whatever opto-isolator I could easily get
Click to expand...
before I'd start messing with making one. That scrap computer power supply
lying on the sidewalk should offer up an opto-isolator, as would that scrap
modem that nobody wants because it's 1200baud. They may not be the best
choice for the fast rate of MIDI, but I suspect they'd work better than
someone making an opto-isolator.

Michael
 
Well, after doing a little searching on the internet, I discovered that
a two-lead phototransistor is not as fast as I thought it was.
Evidently, it takes about ten microseconds to turn off. This still
gives me plenty of margin. Just not as much as I thought I had.
 
MikeMandaville wrote:
Evidently, it takes about ten microseconds to turn off. This still
gives me plenty of margin.
Click to expand...
Ten microseconds is one-third of a bit time. I'd hardly call that
plenty. Just go and buy a 6N138 and stop bugging us with your crazy
notions.
 
"Ken Taylor" (ken123@xtra.co.nz) writes:
MikeMandaville@aol.com> wrote in message
news:1104888479.412702.14490@f14g2000cwb.googlegroups.com...
Hello. I'm building a MIDI interface...

http://www.midi.org/about-midi/electrical.shtml

...and I'm planning on using off-the-shelf Radio Shack components to
build my own opto-isolator. Does anyone know of any reason why I
should not?

Why would you do that? Radioshack sell a perfectly adequate TLP620, which
will at least have known characteristics. Unless of course the object of
your exercise is to learn about making optocouplers rather than MIDI
systems.....

Cheers.

Ken


It's been years since I've seen any MIDI construction articles, but
Click to expand...
back then they all tended to specify a specific opto-isolator, with
comments about how it needed certain specs to match the MIDI specs.

I have no idea how critical it was, and indeed there were construction
articles that used average opto-isolators.

But in reading the original post, I just assumed he was talking not
of building an opto-isolator, but in using whatever Radio Shack still
stocked rather than tracking down the one that was commonly specified.

Michael
 
"Michael Black" <et472@FreeNet.Carleton.CA> wrote in message
news:crfnpl$982$1@theodyn.ncf.ca...
"Ken Taylor" (ken123@xtra.co.nz) writes:
MikeMandaville@aol.com> wrote in message
news:1104888479.412702.14490@f14g2000cwb.googlegroups.com...
Hello. I'm building a MIDI interface...

http://www.midi.org/about-midi/electrical.shtml

...and I'm planning on using off-the-shelf Radio Shack components to
build my own opto-isolator. Does anyone know of any reason why I
should not?

Why would you do that? Radioshack sell a perfectly adequate TLP620,
which
will at least have known characteristics. Unless of course the object of
your exercise is to learn about making optocouplers rather than MIDI
systems.....

Cheers.

Ken


It's been years since I've seen any MIDI construction articles, but
back then they all tended to specify a specific opto-isolator, with
comments about how it needed certain specs to match the MIDI specs.

I have no idea how critical it was, and indeed there were construction
articles that used average opto-isolators.

But in reading the original post, I just assumed he was talking not
of building an opto-isolator, but in using whatever Radio Shack still
stocked rather than tracking down the one that was commonly specified.

Michael


That makes more sense. Sorry, a dim day. Still in New Year's mode (usually
Click to expand...
only lasts till October......)

Ken
 
"MikeMandaville" <MikeMandaville@aol.com> wrote in message
news:1104978126.977791.306170@f14g2000cwb.googlegroups.com...
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.
Click to expand...
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
 
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
 
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