Walkmellotron: Cassette Player Mods

DIY MIDI/Voltage Controlled Controlled Tape Players

by John Park and Liz Clark

published June 29, 2022, last edited January 22, 2025

posted in Hacks Robotics & CNC CircuitPython Breakout Boards/ Motor Controls

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Intermediate

Project guide

Code the Walkmellotron

First make sure you are running the latest version of Adafruit CircuitPython for your board.

Text Editor

Adafruit recommends using the Mu editor for using your CircuitPython code with the Feather. You can get more info in this guide.

Alternatively, you can use any text editor that saves text files.

Download the Project Bundle

Your project will use a specific set of CircuitPython libraries and the code.py file. To get everything you need, click on the Download Project Bundle link below, and uncompress the .zip file.

Drag the contents of the uncompressed bundle directory onto your QT Py board's CIRCUITPY drive, replacing any existing files or directories with the same names, and adding any new ones that are necessary.

Download Project Bundle

Copy Code

# SPDX-FileCopyrightText: 2022 John Park for Adafruit Industries
# SPDX-License-Identifier: MIT

import time
import board
import busio
import adafruit_mcp4728
import usb_midi
import adafruit_midi
from adafruit_midi.note_on import NoteOn

i2c = busio.I2C(board.SCL1, board.SDA1)  # qt py rp2040 amirite
mcp4728 = adafruit_mcp4728.MCP4728(i2c)

FULL_VREF_RAW_VALUE = 4095

mcp4728.channel_a.raw_value = FULL_VREF_RAW_VALUE
mcp4728.channel_a.vref = adafruit_mcp4728.Vref.INTERNAL
mcp4728.channel_a.gain = 2

time.sleep(1)  # settle
volts_per_note = 0.0833  # 1/12th V for 1V/Oct

def midi_to_mv(note):
    notemv = 1000 * (note * volts_per_note)
    return int(notemv)


midi = adafruit_midi.MIDI(
    midi_in=usb_midi.ports[0], in_channel=0, midi_out=usb_midi.ports[1], out_channel=0
)


while True:
    msg = midi.receive()
    if msg is not None:
        if isinstance(msg, NoteOn):
            string_msg = 'NoteOn'
            #  get note number
            string_val = str(msg.note)
            # print("\nnote:",string_val)
            if msg.note < 32:
                mv = midi_to_mv(msg.note)
                # print(mv*0.001, "V")
                mcp4728.channel_a.raw_value = (mv)

# SPDX-FileCopyrightText: 2022 John Park for Adafruit Industries
# SPDX-License-Identifier: MIT

import time
import board
import busio
import adafruit_mcp4728
import usb_midi
import adafruit_midi
from adafruit_midi.note_on import NoteOn

i2c = busio.I2C(board.SCL1, board.SDA1)  # qt py rp2040 amirite
mcp4728 = adafruit_mcp4728.MCP4728(i2c)

FULL_VREF_RAW_VALUE = 4095

mcp4728.channel_a.raw_value = FULL_VREF_RAW_VALUE
mcp4728.channel_a.vref = adafruit_mcp4728.Vref.INTERNAL
mcp4728.channel_a.gain = 2

time.sleep(1)  # settle
volts_per_note = 0.0833  # 1/12th V for 1V/Oct

def midi_to_mv(note):
    notemv = 1000 * (note * volts_per_note)
    return int(notemv)


midi = adafruit_midi.MIDI(
    midi_in=usb_midi.ports[0], in_channel=0, midi_out=usb_midi.ports[1], out_channel=0
)


while True:
    msg = midi.receive()
    if msg is not None:
        if isinstance(msg, NoteOn):
            string_msg = 'NoteOn'
            #  get note number
            string_val = str(msg.note)
            # print("\nnote:",string_val)
            if msg.note < 32:
                mv = midi_to_mv(msg.note)
                # print(mv*0.001, "V")
                mcp4728.channel_a.raw_value = (mv)

Next you can hook up your Walkmellotron and play!

Page last edited January 22, 2025