This project requires two code files, boot.py and code.py.

boot.py

Inside boot.py the USB microphone USB endpoint is enabled and audio settings are configured.

# SPDX-FileCopyrightText: 2026 Tim Cocks for Adafruit Industries
#
# SPDX-License-Identifier: MIT
import usb_audio

usb_audio.enable(
    sample_rate=16000, channel_count=1, bits_per_sample=16, microphone=True
)

1
2
3
4
5
6
7
8

# SPDX-FileCopyrightText: 2026 Tim Cocks for Adafruit Industries
#
# SPDX-License-Identifier: MIT
import usb_audio

usb_audio.enable(
    sample_rate=16000, channel_count=1, bits_per_sample=16, microphone=True
)

code.py

The main project code file is split into the following sections.

Configuration

The first section contains a handful of configuration variables. The pre-loaded message strings BTN_A_MESSAGE and BTN_B_MESSAGE are used for the built-in A and B button hotkey messages, change them to use customized messages.

UNIT_SECONDS is the length in seconds of a single unit in the Morse playback. In standard Morse code, the dot beep lasts one unit of time. Increase the number to make the automatic messages play slower. This value has no effect on live keyed Morse code.

The remaining duration and gap variables are all set relative to UNIT_SECONDS. They use multiples of UNIT_SECONDS based on the standards of International Morse code. Typically you don't want to change them directly, instead just change UNIT_SECONDS. But, you can experiment with different values for them if you don't mind breaking from the protocol specification.

Morse Code Table

Setup

The setup section initializes synthio and usb_microphone and sets synthio to play into the microphone audio stream. Two helper functions are defined:

• play_tone() plays a tone for a specified duration and then stops
• play_morse() accepts a string of text, automatically converts it to Morse code, and plays it into the USB audio stream.

The buttons are initialized using the keypad module. One instance is of keypad.Keys is used for the built-in A and B buttons, and another instance for the Morse key IO pin.

Main Loop

Inside the main loop the code checks both keypad.Keys instances for events to handle. The built-in buttons call play_morse() with their respective string when pressed. The Morse key button plays a tone with synthio when pressed, and stops the tone when released.