Adafruit Slider Trinkey

Half USB Key, half Adafruit Trinket, half mini slide pot!

published June 16, 2021, last edited September 30, 2025
last major update June 23, 2021

posted in Adafruit Products LEDs/ LED Pixels Arduino Compatibles/ Trinket CircuitPython Programming/ MicroPython / CircuitPython

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Beginner

Product guide

MIDI CC Cross Fader

You can use your Slider Trinkey as a MIDI CC cross fader! The CircuitPython analogio module and the Adafruit CircuitPython MIDI library allow you to use the Slider Trinkey to send MIDI CC commands.

Code

Click the Download Project Bundle button below to download the necessary libraries and the code.py file in a zip file. Extract the contents of the zip file, and copy the entire lib folder and the code.py file to your CIRCUITPY drive.

Your CIRCUITPY drive should now look similar to the following image:

Download Project Bundle

Copy Code

# SPDX-FileCopyrightText: 2021 Kattni Rembor for Adafruit Industries
#
# SPDX-License-Identifier: MIT

import time
import board
import analogio
import usb_midi
import adafruit_midi
import neopixel
from adafruit_midi.control_change import ControlChange

pixels = neopixel.NeoPixel(board.NEOPIXEL, 2, brightness=1)

slider = analogio.AnalogIn(board.POTENTIOMETER)
position = slider.value  # ranges from 0-65535


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

last_cc_val = 0


# ------- Hue/Sat/Val function to convert to RGB  ------ #
def hsv2rgb(h, s, v):
    """
    Convert H,S,V in 0-255,0-255,0-255 format
    to R,G,B in 0-255,0-255,0-255 format
    Converts an integer HSV (value range from 0 to 255) to an RGB tuple
    """
    if s == 0:
        return v, v, v
    h = h/255
    s = s/255
    v = v/255
    i = int(h * 6.0)
    f = (h * 6.0) - i
    p = v * (1.0 - s)
    q = v * (1.0 - s * f)
    t = v * (1.0 - s * (1.0 - f))
    i = i % 6
    if i == 0:
        r, g, b = v, t, p
    if i == 1:
        r, g, b = q, v, p
    if i == 2:
        r, g, b = p, v, t
    if i == 3:
        r, g, b = p, q, v
    if i == 4:
        r, g, b = t, p, v
    if i == 5:
        r, g, b = v, p, q
    return int(r * 255), int(g * 255), int(b * 255)


hue_a = 0
sat_a = 255
val_a = 255
color_a = hsv2rgb(hue_a, sat_a, val_a)

hue_b = 127
sat_b = 255
val_b = 255
color_b = hsv2rgb(hue_b, sat_b, val_b)

pixels[0] = color_a
pixels[1] = color_b

while True:
    cc_val = slider.value // 512  # make 0-127 range for MIDI CC

    if abs(cc_val - last_cc_val) > 2:
        print(cc_val)
        last_cc_val = cc_val
        mod_wheel = ControlChange(1, cc_val)
        midi.send(mod_wheel)
        color_a = hsv2rgb(cc_val, sat_a, val_a)
        pixels[0] = color_a
        color_b = hsv2rgb(cc_val, sat_b, val_b)
        pixels[1] = color_b
        time.sleep(0.001)

# SPDX-FileCopyrightText: 2021 Kattni Rembor for Adafruit Industries
#
# SPDX-License-Identifier: MIT

import time
import board
import analogio
import usb_midi
import adafruit_midi
import neopixel
from adafruit_midi.control_change import ControlChange

pixels = neopixel.NeoPixel(board.NEOPIXEL, 2, brightness=1)

slider = analogio.AnalogIn(board.POTENTIOMETER)
position = slider.value  # ranges from 0-65535


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

last_cc_val = 0


# ------- Hue/Sat/Val function to convert to RGB  ------ #
def hsv2rgb(h, s, v):
    """
    Convert H,S,V in 0-255,0-255,0-255 format
    to R,G,B in 0-255,0-255,0-255 format
    Converts an integer HSV (value range from 0 to 255) to an RGB tuple
    """
    if s == 0:
        return v, v, v
    h = h/255
    s = s/255
    v = v/255
    i = int(h * 6.0)
    f = (h * 6.0) - i
    p = v * (1.0 - s)
    q = v * (1.0 - s * f)
    t = v * (1.0 - s * (1.0 - f))
    i = i % 6
    if i == 0:
        r, g, b = v, t, p
    if i == 1:
        r, g, b = q, v, p
    if i == 2:
        r, g, b = p, v, t
    if i == 3:
        r, g, b = p, q, v
    if i == 4:
        r, g, b = t, p, v
    if i == 5:
        r, g, b = v, p, q
    return int(r * 255), int(g * 255), int(b * 255)


hue_a = 0
sat_a = 255
val_a = 255
color_a = hsv2rgb(hue_a, sat_a, val_a)

hue_b = 127
sat_b = 255
val_b = 255
color_b = hsv2rgb(hue_b, sat_b, val_b)

pixels[0] = color_a
pixels[1] = color_b

while True:
    cc_val = slider.value // 512  # make 0-127 range for MIDI CC

    if abs(cc_val - last_cc_val) > 2:
        print(cc_val)
        last_cc_val = cc_val
        mod_wheel = ControlChange(1, cc_val)
        midi.send(mod_wheel)
        color_a = hsv2rgb(cc_val, sat_a, val_a)
        pixels[0] = color_a
        color_b = hsv2rgb(cc_val, sat_b, val_b)
        pixels[1] = color_b
        time.sleep(0.001)

Usage

Check out the video above for a demo and code explainer!

You can use the code to control any MIDI CC parameter you like in pretty much any synth or DJ software, as well as any hardware synths that can act as a USB host.

If necessary, you can also adjust the MIDI channel and CC number in code. By default this uses MIDI channel 1 and CC number 1 -- a.k.a, Mod Wheel.

Page last edited January 22, 2025