Forum Rule: Always post complete source code & details to reproduce any issue!
Results 1 to 6 of 6

Thread: Schematic reading help MIDI IN DIN

  1. #1
    Junior Member
    Join Date
    Mar 2020
    Posts
    2

    Schematic reading help MIDI IN DIN

    Hi,

    I'm a beginner at this kind of electronic stuff, I never used a Tennsy only Arduino. What are the two diodes at between the 220 resistor and the pc900? And do I need them for my midi input circuit to work?

    Thank you!


    Click image for larger version. 

Name:	midiin.png 
Views:	10 
Size:	7.1 KB 
ID:	19396

  2. #2
    Senior Member oddson's Avatar
    Join Date
    Feb 2013
    Location
    Isle in the Salish Sea
    Posts
    1,340
    First, there is only one as the second is inside the PC900. The inside one is a current switch on the internal buffer

    Second, that's schematic is specifically for T2.0 and are you really using that?

    Third, there should always be three things in a short list!

    ...but I'm fairly sure it's polarity protection in case the MIDI In current has been reversed somehow. And similarly for the T3.x version above on the MIDI page.
    https://www.pjrc.com/teensy/td_libs_MIDI.html

  3. #3
    Junior Member
    Join Date
    Mar 2020
    Posts
    2
    Quote Originally Posted by oddson View Post
    First, there is only one as the second is inside the PC900. The inside one is a current switch on the internal buffer

    Second, that's schematic is specifically for T2.0 and are you really using that?

    Third, there should always be three things in a short list!

    ...but I'm fairly sure it's polarity protection in case the MIDI In current has been reversed somehow. And similarly for the T3.x version above on the MIDI page.
    https://www.pjrc.com/teensy/td_libs_MIDI.html
    Yes I will be using a 2.0 since the project I'm currently attempting to do use it. So I don't really need the diode if I'm using the MIDI connector "as intended"?

    Attachment 19397

  4. #4
    Senior Member oddson's Avatar
    Join Date
    Feb 2013
    Location
    Isle in the Salish Sea
    Posts
    1,340
    You don't need it if you never need it.

    Getting that wiring wrong on an out or thru circuit is really easy as it's not immediately clear which direction the wiring diagram is meant to show; face or contact side?

    The fact it's standard suggests it happens.... the part is a few cents... add it if you can.

  5. #5
    The PC900 opto-isolator has been long since discontinued. Use a 6N137 in it's place. The pin out is different, but there are plenty of example circuits for MIDI in. A 6N138 based circuit would be fine too.

  6. #6
    Senior Member
    Join Date
    Nov 2012
    Location
    Boston, MA, USA
    Posts
    1,111
    (CA-033) MIDI 1.0 Electrical Specification Update [2014], available on MIDI.org (free, requires registration for download) has a lot more detail than the original and very sketchy MIDI 1.0 electrical "specification". In particular it adds details for changes to the MIDI out low voltage signalling, explains the current loop operation, and suggests changes for electromagnetic screening. In general it is a lot better written.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •