Trinket M0 and GEMMA M0 boards can run CircuitPython — a different approach to programming compared to Arduino sketches. In fact, CircuitPython comes factory pre-loaded on these boards. If you’ve overwritten it with an Arduino sketch, or just want to learn the basics of setting up and using CircuitPython, this is explained in the Adafruit Trinket M0 and Adafruit GEMMA M0 guides.

These directions are specific to the “M0” boards. The original Trinket & GEMMA with an 8-bit AVR microcontroller don’t run CircuitPython…for those boards, use the Arduino sketch on the “Arduino code” page of this guide.

Below is CircuitPython code that works similarly to the Arduino sketch shown on the prior page. To use this, plug the Trinket/GEMMA M0 into USB…it should show up on your computer as a small flash drive…then edit the file “” with your text editor of choice. Select and copy the code below and paste it into that file, entirely replacing its contents (don’t mix it in with lingering bits of old code). When you save the file, the code should start running almost immediately (if not, see notes at the bottom of this page).

If Trinket or GEMMA M0 doesn’t show up as a drive, follow the corresponding guide link above to prepare the board for CircuitPython.

This code requires version 2.1 or later of CircuitPython. Earlier versions didn’t yet support PWM output. The Trinket M0 or Gemma M0 introductory guides explain how to load or update CircuitPython if needed.
# SPDX-FileCopyrightText: 2017 Limor Fried/ladyada for Adafruit Industries
# SPDX-FileCopyrightText: 2017 Phillip Burgess for Adafruit Industries
# SPDX-License-Identifier: MIT

Adafruit Trinket/Gemma Example: Simple Theramin
Read the voltage from a Cadmium Sulfide (CdS) photocell voltage
divider and output a corresponding tone to a piezo buzzer

Photocell voltage divider center wire to GPIO #2 (analog 1)
and output tone to GPIO #0 (digital 0)

import time

import analogio
import board
import pwmio

photocell_pin = board.A1  # CdS photocell connected to this ANALOG pin
speaker_pin = board.D0  # Speaker is connected to this DIGITAL pin
scale = 0.03  # Change this to adjust tone scale

# Initialize input/output pins
photocell = analogio.AnalogIn(photocell_pin)
pwm = pwmio.PWMOut(speaker_pin, variable_frequency=True, duty_cycle=0)

while True:  # Loop forever...
    # Read photocell analog pin and convert voltage to frequency
    pwm.frequency = 220 + int(scale * float(photocell.value))
    pwm.duty_cycle = 32767  # 50% duty cycle
    time.sleep(0.4)  # Play for 400 ms (adjust to your liking)
    pwm.duty_cycle = 0  # Stop playing
    time.sleep(0.05)  # Delay 50 ms between notes (also adjustable)

This guide was first published on Sep 19, 2013. It was last updated on Sep 19, 2013.

This page (CircuitPython Code) was last updated on Nov 22, 2021.

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