MIDI in does not work

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When MIDI data arrives in the Shruthi-1, an icon is shown in the corner of the display. The icon is:

  • A note for note messages.
  • A ~ for controllers.
  • A pitch bend lever for pitch bend.

If these icons show up and you don't get sound, make sure that the master keyboard is sending to the same channel the Shruthi-1 is listening to.

If you cannot see those icons, check that the 6N137 optocoupler is correctly inserted - and that you have not swapped it with the other DIP8 chip (the EEPROM).

6n137.jpg

Check that the voltage at pin 8 is +5V. Disconnect the power and check that pin 5 is continuous with ground. If not, resolder the pins of the optocoupler.

With the unit powered, check that pin 6 is at +5V and temporarily falls down when MIDI messages are sent.

Here is a scope trace:

5108372380_52d0ff01b2_z.jpg