Last Updated or created 2025-10-01

Yesterday I got my new signal generator (FY6900), my DIY version was missing functions.
Now I can test my op-amp schematic I’ve been posting about.

MIDI Controller

Next, for my YM2203 player, I wanted to make this Midi Controllable.
But I don’t have a Midi Controller which has enough knobs and keys.
Besides that, I thought it was cool to build my own.

• Teensy 4.0 (because I needed multiple analogue inputs, I used another controller before, with an analogue multiplexer. But I wanted to use the easy method to use USB as midi also.
  The board will also have midi connectors, but not populated yet.
  So you can use both.
• SSD1306 display (for now)
  Showing note being played and two potentiometer values.
• Two potentiometers (for now) I can use these separately. But when pressing the last key on the key matrix, it will change the CC Channel of the first pot. (Using the value of the second)
• 4×4 Matrix keyboard being read by a MCP23017 I2C 16-bit GPIO Expander. Both display and GPIO expander are on the same bus.

MCP23017 pinout

I used some pullups on : /RESET and GPA0-3
Pullups not needed on SDA/CLK because these are on the display board.