How to change the MIDI input circuit for 6N137 instead of 6N138?

D

dannytaurus

Member
I'm trying to figure out what modifications to make to the MIDI input section of this circuit to use 6N137 IC instead of the 6N138 shown.

td_libs_MIDI_sch_t3.png

In my searches I'm finding incomplete and conflicting info. Any solid answer? (I'm using Teensy 4.0 and 4.1 if that makes a difference)
 
Thanks for the link jimr but I decided to go the easy route and source some 6N138 instead. I see a lot of conflicting information about the 6N137 and I'm too new to this to make sense of it.
 
dannytaurus said:
Thanks for the link jimr but I decided to go the easy route and source some 6N138 instead. I see a lot of conflicting information about the 6N137 and I'm too new to this to make sense of it.
Click to expand...

@dannytaurus:

Have a look at <this thread>, which appears to describe a successful implementation with the 6N137.

Mark J Culross
KD5RXT
 
While not qualified to say, what I read is the 137 can tolerate a much higher impedance pullup and so the using the internal one makes sense to me.

I believe lower value pullups would still work and that higher values are recommended to mitigate high-frequency noise from the fast switching speed.

The Darlington pair in the 138 switches much more slowly and needs a more aggressive (lower impedance) pull-up to work, even an MIDI speeds.
 
kd5rxt-mark said:
@dannytaurus:

Have a look at <this thread>, which appears to describe a successful implementation with the 6N137.

Mark J Culross
KD5RXT
Click to expand...

Sorry, apparently my phone corrupted the pasted thread link . . . it's <here>.

Note that one of the posts in this same thread seems to imply that the output from the 6n137 is inverted from the normally used 6n138 opto-isolator, so you may be bumping into that as well. The thread includes a couple of possible work-arounds which should allow you to make use of the 6n137.

Mark J Culross
KD5RXT
 
Try this:-

Code: 
#include <MIDI.h>
MIDI_CREATE_INSTANCE(HardwareSerial, Serial1, MIDI); // MIDI library init

void setup() {
  MIDI.setHandleNoteOn(midiNoteOnCallback);
  MIDI.begin();
  Serial1.begin(31250,SERIAL_8N1_RXINV);
}

void loop() {
  MIDI.read();
}
 
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