MIDI in does not work
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).
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: