Use
The only wiring required is to connect the 3.5mm cable plug into the Morse code key and connect the alligator clips on the other end of the 3.5mm cable to pins A1 (white wire) and GND (black wire) on the Circuit Playground Bluefruit.
With the project boot.py and code.py files running on the Circuit Playground Bluefruit, the board will appear to the computer as a USB microphone in addition to the usual CIRCUITPY drive and serial console.
The exact steps to select it for a given application will vary. Generally you'll need to either set the CPB as your system default mic in the system settings (Ubuntu Sound input settings screenshot shown here), or set the input within a specific application such as Audacity or Discord.
In Audacity, click Audio Setup -> Recording Devices, then click on Circuit Playground Bluefruit USB Audio in the list of devices.
In Discord click the dropdown arrow on the red microphone button, then click Input Devices -> Circuit Playground Bluefruit Mono
Pressing the Morse code key will generate a tone into the audio stream via USB to the computer. Use a short press for a dot, and a 3x longer press for a dash. Refer to a Morse code chart if you're new to Morse or need a refresher on the alphabet. See if you can decode the short Morse code message keyed with the device from the wave file recording below.
Preprogrammed Messages
The code allows you to have up to two preprogrammed messages. They are stored as string variables in code.py and can be sent with the built-in A and B buttons on the CPB. Change the value of the two variables near the top of the code.
BTN_A_MESSAGE = "HELLO WORLD" BTN_B_MESSAGE = "CIRCUITPYTHON"
Press the A or B button on the CPB to automatically convert the specified message to Morse code and play it into the USB audio stream.
Page last edited June 29, 2026
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