Trinkey MIDI Theramin (will also work on any other CircuitPython devices with `touchio`)

trinkey_theramin_code.py

# trinkey_theramin_code.py -- Trinkey Theramin!  (not a theremin! :)
# 2021 @todbot
#  left antenna: note on, then filter resonance
# right antenna: filter cutoff
#
import time
import board
import neopixel
import touchio
import usb_midi
import adafruit_midi
from adafruit_midi.note_on          import NoteOn
from adafruit_midi.control_change   import ControlChange

midi = adafruit_midi.MIDI(midi_out=usb_midi.ports[1], out_channel=0)
leds = neopixel.NeoPixel(board.NEOPIXEL, 4, brightness=0.2, auto_write=True)

# announce we're alive and wait for things to stabilize
# before creating touch pins so their raw_value baseline are okay
leds.fill(0xff00ff)
time.sleep(1.0)
leds.fill(0)

touch1_pin = touchio.TouchIn(board.TOUCH1)
touch2_pin = touchio.TouchIn(board.TOUCH2)

# a litlte helper class for noise filtering
class RunningAverage:
    def __init__(self,count):
        self.count = count
        self.i = 0
        self.buf = [0] * self.count
    def add_value(self,val):
        self.buf[self.i] = val
        self.i = (self.i + 1) % self.count
    def average(self):
        return sum(self.buf)/self.count

base1 = int(touch1_pin.raw_value * 1.02)
base2 = int(touch2_pin.raw_value * 1.02)

avg1 = RunningAverage(8)
avg2 = RunningAverage(8)

note_on = False

note = 60  # C4 in MIDI land
velocity = 64  # half 

while True:
    avg1.add_value( touch1_pin.raw_value )
    avg2.add_value( touch2_pin.raw_value )

    r = 0
    g = min(max(avg1.average()-base1, 0),255)
    b = min(max(avg2.average()-base2, 0),255)
    
    leds.fill( (r,g,b) )

    if g > 10:   # hand present
        if not note_on:
            midi.send(NoteOn(note, velocity))
            print(time.monotonic(),"******* ON!")
            note_on = True
    else:
        if note_on:
            midi.send(NoteOn(note, 0)) # release
            print("------ OFF!")
            note_on = False

    if g > 10:  # hand present
        midi.send(ControlChange(71, 64+int(g//4))) # 71 = filter resonance
        
    if b > 10:  # hand present
        midi.send(ControlChange(74, 64+int(b//4)))  # 74 = filter cutoff

    time.sleep(0.001)

Video demo:

trinkey_midi_theremin_filter.mp4