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Thread: Midi PCB

  1. #1

    Midi PCB

    Hello,

    I'm making a stab at building my first PCB using GEDA. It's a copy of the schematic PJRC posted https://www.pjrc.com/teensy/td_libs_MIDI_sch.gif
    so I can start mucking around with the teensy audio board for synth stuff using my midi controller.

    I was hoping someone could verify I didn't do anything grossly wrong before I ship it to get made.

    https://github.com/jjrh/midi_shield is the github with all the project files and some renders of the board.

    Thanks!

    -jjrh.

  2. #2
    Senior Member PaulStoffregen's Avatar
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    Are you sure you want to connect the shield of MIDI-IN to ground?

    Looks like you have traces that depend on connectivity across some large holes for the connectors, which don't have an annular ring. You might look into whether those connections will be made.

    With diodes, it's common practice to add a mark on the silk screen layer to indicate the cathode side. While this doesn't affect the PCB traces at all, it is really helpful when you later solder the parts.

  3. #3
    Quote Originally Posted by PaulStoffregen View Post
    Are you sure you want to connect the shield of MIDI-IN to ground?
    I thought the shield was supposed to be connected to ground?

    Quote Originally Posted by PaulStoffregen View Post
    Looks like you have traces that depend on connectivity across some large holes for the connectors, which don't have an annular ring. You might look into whether those connections will be made.
    Thanks, I'll look into it.

    Quote Originally Posted by PaulStoffregen View Post
    With diodes, it's common practice to add a mark on the silk screen layer to indicate the cathode side. While this doesn't affect the PCB traces at all, it is really helpful when you later solder the parts.
    Good call didn't think of that!

  4. #4
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    Quote Originally Posted by jjrh View Post
    I thought the shield was supposed to be connected to ground?
    At one end, yes (the MIDI out). That provides shielding. By not conecting both ends, MIDI avoids ground loops (the opto-coupling also avoids this). See the connection diagram and photos at
    http://www.pjrc.com/teensy/td_libs_MIDI.html

  5. #5
    Okay I made the suggested changes (I think) annular rings should be bigger. I removed the 'extra pins' connectors which just added complexity. I sent the midi in shield to NC.

    I also fixed a issue where the pins to the teensy were connected that shouldn't have been.

    Let me know if I missed anything! (you can compare https://github.com/jjrh/midi_shield/...0c92d841744b79 for the PCB renders and https://github.com/jjrh/midi_shield/...67cbb6881d92ec for the schematic)

  6. #6
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    Which Teensy is this for - a 5V one like Teensy 2.0 / Teensy++ 2.0 or a 3V3 one like Teensy 3.0/3.1/LC?

  7. #7
    Going to be a teensy 3.1 (it's so I can do work with the audio shield)

    I guess I should add room for the two resistors on the midi out.

    Room for a dip switch might be cute.

  8. #8
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    In that case, be sure to read http://www.pjrc.com/teensy/td_libs_MIDI.html because the resistor values in your schematic are for 5V.

  9. #9
    Teensy 3.0: Use two 47 ohm resistors on MIDI OUT, with the pin 4 resistor to +3.3 volts. For MIDI IN, connect the 270 ohm resistor to +3.3 volts. (TODO: add a Teensy 3.0 specific schematic here)
    are the two 47ohm resisters in parallel or series?

    Is the midi in 270 ohm resister the one on pin4 of the PC900?

  10. #10
    Okay updated the schematic to be for the 3.3v. (I assumed those resisters are in series)

    Click image for larger version. 

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    Click image for larger version. 

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    Click image for larger version. 

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  11. #11
    Just thought I would say I successfully got the boards made from seeedstudio.

    I had one mistake, the diode silkscreen (maybe also in the schematic? - I should check...) is backwards. I discovered this after spending more time than I would like to admit debugging the board.

    At some point I'll fix this up.
    I also should also put better labels on the pinout.
    I can probably also pretty easily do the layout to be 5v or 3.3v.
    Seeedstudio did the drill holes which I guess in the gerber file weren't all the way through the board.

    I can probably condense everything further and use thinner traces.

    Paul, if you see this feel free to update http://www.pjrc.com/teensy/td_libs_MIDI.html to include my schematic.

    Click image for larger version. 

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