This project was conceived to connect controls to Virtual Pipe Organ software such as Hauptwerk, Grande Orgue, Cecilia etc running on a touch screen laptop. The design uses an inexpensive microcontroller board with few external components. Flexibility is the main motivation as I started with little Midi or VPO experience. This project may work for you too. Let me know how you get on and whether improvements should be made.

• Hosted on the STM32 Blue Pill, a $2US development board
• USB Connection to host computer, LED blink on Midi activity
• Multiple STM32 boards may be deployed to ease wiring or increase capacity
• 80 scanned contacts arranged as a 8 input x 10 output diode switch matrix
• Contacts may send Midi Note On/Off messages for pedalboard, stops, couplers or toe pistons
• Contacts may instead send Keyboard HID messages for turning music pages displayed on a host computer monitor
• Page turning may use a single sustain pedal type contact e.g. short press forward, long press back.
• Contacts and potentiometers are individually debounced for 50ms to reduce message floods
• Tested using Arduino V1.8.19 with STM32 extensions under Ubuntu 22.04 X86 & Arm Linux
• Active High Outputs for the best noise immunity connect to inputs via a diode and switch:
• Output-----|>|---Switch----Input
• Up to 8 ADC inputs may be used for expression pedals and other purposes.
• Up to 8 I2C 16 x 2 line LCDs show their auto detected i2c address at power on.

• 80 Pedalboard inputs in 10x8 matrix mapped to Midi Channel 3/4 Note 36-67 (C2-G4) and 4 HID keybd buttons for page turning
• 96 Button & LED Shift register IO's mapped to Midi Channels 5-8 Notes 1-24 for pistons or stops
• 8 Filter ADC inputs are mapped to Channel 9 Midi CC 20-27 values 0-127 for expression pedals and LED dimming
• I2C Display addresses are configured by PCF8574 solder bridge inputs on the LCD modules, these addresses are then configured in Hauptwerk and map through the blue pill. Expect address 0x38-0x3f for Philips/NXP ICs and 0x20-0x27 for TI. The highest address is used when no solder bridges are fitted.

Initial midi channel assignments are readily altered by editing constant arrays.

• The firmware is configured to use the reserved gpio pins, the Blue Pill may be tricky to re-program.
• To re-program if you have problems:
• 1. Set Boot0 Link to position 1
• 2. Press reset
• 3. Upon releasing reset immediately upload new code using ST-Link
• 4. Repeat step 3 until programming success
• 5. Move Boot0 link to position 0
• 6. Disconnect programmer
• 7. OR Use a USB boot loader

• Output drive for LEDs and displays possibly midi controlled may be needed

The code is based on the excellent examples from: https://github.com/arpruss/USBComposite_stm32f1/tree/master/examples Also thanks to the Arduino and STM32 support teams

MIT