SYNTH-MIDI-CTL-01

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SYNTH-MIDI CTL-01 REV1 FRONT 3D.png

Features[edit]

  • Adapted from HAGIWO's MIDI to CV module
    • Translate from Japanese to English using browser
  • XAIO RP2040 CPU
    • Arduino MIDI library has not yet been ported to Pico so will need to use CircuitPython MIDI Library
  • MIDI In/Out
    • Standard MIDI Jacks
    • MIDI out jack for future functionality
  • (2) 0-5V Analog CV outs
  • (2) Digital Outs, eX:
    • Gate
    • Clock
  • Pot supports setting Clock rate
  • Standard EuroRack 16 pin header
    • Supports 12V in with on-board 5V regulator
    • 5V regulator can be not installed if 5V is available on EuroRack connection
  • Card is not a Eurorack card
    • Probably too deep, needs cabling
  • (6) 6-32 Mounting holes

RP2040 Pin Assignments[edit]

  • Pins
    • A0, P26 = CLK_POT
    • D2 = SPI_SS
    • D3 = Gate (Out)
    • D4 = MIDI Clk (Out)
    • D5 = SPI_LDAC
    • D6/TX - MIDI_Out
    • D7/RX = MIDI In
    • D8 = SPI_SCK
    • D9 = Unused
    • D10 = MOSI

Connectors[edit]

MIDI-CTRL-01 REV-1 CAD.PNG

H1 - Use +12V[edit]

J1 - Power[edit]

  • Eurorack compatible pinout
  • Fits a shrouded connector with some interference with Voltage Regulator U1

J2, J3 - Digital Outs[edit]

J4 - MIDI In[edit]

J5, J7 - Control Voltages (CV) Out[edit]

  • CVs are generated by MCP4822 12-bit D/A
  • Output amplifier shifts 0-3.3V from A/D to 0-5V for CV

Note to CV Mapping[edit]

C2 = First Note On = 36 velocity 100, Note CV = 0, volts 0.0
C3 = First Note On = 48 velocity 100, Note CV = 819, volts 0.999756
C4 = First Note On = 60 velocity 100, Note CV = 1638, volts 1.99951
C5 = First Note On = 72 velocity 100, Note CV = 2458, volts 3.00049
C6 = First Note On = 84 velocity 100, Note CV = 3277, volts 4.00024
C7 = First Note On = 96 velocity 100, Note CV = 4095, volts 4.99878

CV Scaling[edit]

  • RP2040 runs at 3.3V
  • MCP4822 Dual D/A runs at 3.3V
    • Since power supply is 3.3V, can only use the 1X output gain
    • Full-scale voltage = 2.048V
  • Op Amp drivers out
    • Scale output voltage by 5.0/2.048 = 2.4414
    • Non-Inverting Op Amp gain = 1 + (Rf/R_to_Gnd)
    • Rf/R_to_Gnd = 2.4414-1 = 1.4414
      • Rf = 5.6K, R_to_Gnd = 3.9K = 1.436 ratio
        • error = 0.3%, resistors are 2%
  • Can adjust out errors in the Note to CV table

J6 - MIDO Out[edit]

  • Not used but here for future operation
    • Perhaps make USB MIDI to DIN-5 MIDI (In/Out)

Videos[edit]

  • Similar design
  • Arduino NANO and MCP4822 at 5V
  • Could only generate 0-4.096 for 4 octaves?
    • Due to internal 2.048 voltage reference and 2x gain opamp

  • MIDI Clock explained

Software[edit]

  • MIDI 1.0 Control Change Messages
  • HAGIWO 's code runs on an Arduino NANO and was developed in the Arduino IDE
  • However, there's no Arduino MIDI library for the RP2040
  • This is a port of Arduino code to CircuitPython done in pieces

HAGIWO code baseline[edit]

CircuitPython[edit]

SYNTH-MIDI-CTL-01 GitHub repo

SPI Code[edit]

# imports
import board
import busio
import digitalio

# Set up Chip Select pin
cs = digitalio.DigitalInOut(board.D2)
cs.direction = digitalio.Direction.OUTPUT
cs.value = True

# Create an interface to the SPI hardware bus
spi = busio.SPI(board.SCK, MISO=board.MISO)

# Lock the bus

while not spi.try_lock():
    pass

# The busio.SPI.configure() function is called to configure the speed, phase, and polarity of the SPI bus. 
# It’s important to always call configure after locking the bus and before talking to your device as communication 
# with other devices might have changed the speed, polarity, etc.
# You’ll need to look up the exact speed and other values from your device’s datasheet. 
# For the MAX31855 (example) we’ll use a speed of 5mhz and a polarity and phase of 0 (sometimes called mode 0).

spi.configure(baudrate=5000000, phase=0, polarity=0)
cs.value = False

# Read example (not used)
# result = bytearray(4)
# spi.readinto(result)
# cs.value = True
# result
# bytearray(b'\x01\xa8\x1a\xf0')

# Write example
spi.configure(baudrate=5000000, phase=0, polarity=0)
cs.value = False
spi.write(bytes([0x01, 0xFF]))
cs.value = True

# Need to unlock bus when done
spi.unlock()

Issues[edit]

Rev 2[edit]

  • Moved U4 down a bit
  • Add 0.1uF cap MIDI In pin 2 to GND
  • Double inverted clocks
    • Rev 1 had single inversion
  • Will be software difference to invert/not invert clocks
  • Moved MIDI In off 74HC14 since it is 5V out on 74HC14

Rev 1 Checkout[edit]

  • D9 s/b 1N914
  • s/s R1 has 1K, P/L has 2.7K
  • R1 pullup could be moved to Vcc (+5V)
  • DIN-5 J4 could use a 0.1uF cap to logic ground
  • J1 fits with a shrouded connector has some interference with Voltage Regulator U1
  • U4 is connected to 5V power but drives into XIAO - needs to be clamped to 3.3V
  • Cut trace U4-10 (RXD) front side
  • Add wire U4-13 to U2-8 (RXD)
  • Set CV output to 5V
    • Change R9, R15 to 5.6K
    • Change R10, R16 to 3.9K

Assembly Sheet[edit]