Configure each of the MIDI connectors as IN or OUT by software (Arduino)
  • In my current (Arduino) project I have (currently) 3 MIDI INs and 2 MIDI OUTs. However, it would be nice, if I can configure each of the MIDI connectors as IN or OUT by software (Arduino).

    The circuits I am using are:

    (Update: My MIDI Input circuit has a 1N4001 diode instead of 1N914, and between pin 6 to +5v, a 10 Kohm instead of 220 ohm).
    (Update: My MIDI Output circuit has a 10 Kohm resistor instead of a 220 ohm resistor)

    What I would like is to use the connector show in the above picture as MIDI In OR MIDI out. I have not tried it yet, since I have too many doubts and I do not want to break a component. However, I thought about it (with my limited electronic knowledge), and I think:

    Pin 2 afaik for MIDI In, normally has +5V. In the MIDI Input circuit it is not connected, but in the MIDI Output circuit, it is connected to GND. I don't think this is good when being used as MIDI out, resulting in a short circuit (?). So I guess I have to make it +5V when used as MIDI Input and GND when used as MIDI Output (so putting HIGH or LOW 'digital' for Arduino).
    Pins 1 and 3 remain in both circuits untouched (so I assume I can do the same).
    Pin 4 and 5 is a bit tricky, since they are connected. I think I have to use one or two transistors to create two alternative paths for pins 4 and 5 for MIDI Input and Output. Or can I just setting a specific voltage on pins 4 and 5 when used as MIDI In or Out? (and what would those values be?).
    For the MIDI input, an optocoupler is used, while for MIDI output, directly the Arduino is used. I wonder if I have to use for both an optocoupler (since people might connect it 'accidentally' to a MIDI output from a MIDI device.
    And also I'm not sure how to handle the RX and TX pins ... for 5 MIDI devices, I would need to use 5 RX and TX pins, but the Arduino (Mega) only has 4 of each. But this is probably a question for the Arduino board.
    (link to Arduino Stack Exchange question regarding question 5): Arduino question


    Based on the answer of CL:

    About the 220R resistor, capacitor to GND and type of diode: I will have to check if I use those (the example above is more like a generic circuit, mine is already slightly adapter). I will check Friday exactly my circuit.
    Although I'm planning to use a 12V/1A adapter (not sure how yet), still might be better to preserve memory in case I later want to use a battery or 5V from MIDI solution, so thanks for the remark about the other 220R resistor.
    (I do not want to use physical switches, I want it to be (software) configurable, for an output to be MIDI In OR MIDI Out. So that means for a MIDI connector, it should be both connected to the MIDI in AND out circuit, or via a transistor (?), which is controlled by software in the Arduino. But I do not know how to add this transistor into the MIDI In/Out circuit and what kind of transistor to be used ... or maybe there is a better solution ... or not even possible? -> Answered already by replate
    Currently I use a 6N138 without problems, except I noticed when I use the first serial for debugging, the processing is too slow, but I think that is because of performance of the CPU/whatever, not the 6N138. On the other hand, I don't want the Optocoupler to be the weak point in any case, so I will change to another (H11L1 for example).
    According to your items:

    The problem is I don't know beforehand if the right cable is inserted (I will make a different question for this).
    I need somehow to put pins 4 and 5 to both the MIDI IN and MIDI Out circuit. A 'physical' switch (SPDT) will not do. -> answered already by replete
    In that case I don't need to do anything special for this.
    I heard from other sources a software serial is not advised. Also I want to do some processing, but maybe it helps.
    Work in progress update:

    I made the circuit with existing components I have, using a DIP switch instead until I have the CD4053 ( Kynix : ( using 4 dip switches, 2 for MIDI In, pin 2 and 4, and 2 for MIDI Out, pin 2 and 4).
    Using 6N138 ... I will replace them until the H11L1 (DATA:
    Using 1N4014 ... I will replace them until the 1N4148(DATA: arrive.
  • Sounds really interesting, but I was wondering how Audulus enters into this?