xiaoKey

Even yet another electronic iambic keyer.

It is a minimalist device based on:

• an inexpensive Seeed Xiao RP2040 controller board
• CircuitPython programs and libraries

The code directory has the files to be installed on the Seeed Xiao device.

The pcbdirectory has the Eagle schematics for a possible carrier board with connectors.

Features

• Operates as an iambic type B Morse code keyer with a 3.5mm stereo jack to connect to a dual-paddle telegraph key
• Has a configurable side tone transmitted through an on-board piezo buzzer
• Has an open-drain output to a 2.5mm mono jack, which should be able to key most radios (probably not tube sets)
• When connected to a PC over USB appears as two COM ports:
  • One is the CircuitPython REPL and console
  • A second port that shows the characters being transmitted, and also transmits Morse code for characters typed into the COM port
• Has three buttons to trigger canned messages
• Speed, sidetone, keyboard operation, and canned messages are configured by editing the code.py file on the CIRCUITPY: device
• Can act as a USB keyboard, where keyed characters are also sent to the computer as keystrokes.

Software Installation

1. Get the most recent UF2 file for CircuitPython on the Xiao RP2040 here.

2. Connect the Xiao to a computer using a USB C cable.

3. Follow the instructions for loading CircuitPython here. Basically, you put the Xiao in boot loader mode by pressing and holding the BOOT button and tapping the reset button. Then copy the UF2 file to the Xiao which appears as RP1-RP2. The Xiao will now reboot itself.

4. Copy the required library files (in the repository lib directory) to the lib directory on the attached Xiao. The files are:

   • neopixel.mpy
   • The directory adafruit_hid

   The most recent versions of these files can be found here.

5. Copy boot.py and code.py to the Xiao, which now appears as drive CIRCUITPY on the computer.

6. Press the RESET button on the Xiao.

Configuration

The device is configured by editing the source file code.py on the Xiao device. The configuration parameters appear near the top.

# user configuration
WPM = 15
SIDETONE = True
SIDEFREQ = 880
KEYBOARD = False

# user messages
MSG1 = "AC9YW"
MSG2 = "CQ CQ CQ DE AC9YW AC9YW AC9YW K"
MSG3 = "73"

• SIDETONE True will generate a tone on the buzzer when keying, False will disable the local side tone.
• SIDEFREQ is the audio frequency of the side tone sound in Hz. 880 should sound like the musical note A an octave above concert A. The frequency you choose is simply a matter of preference.
• KEYBOARD True will type decoded characters into the attached computers as though typed on a keyboard. Be careful turning this on, as your Morse keying will appear in whatever window currently has focus, which can have unintended effects.
• MSGx Are the contents of the canned messages triggered by the on-board tact buttons

The file code.py should appear as a text file on the CIRCUITPY: device. There are special programs to aid in editing Python programs (such as Mu and Thonny) but most simple text editors should work. Avoid word processing programs that save files in special formats. A discussion of editors for CircuitPython can be found here.

You may have to reset the Xiao after editing for the changes to take effect.

Pinout

                 +---USB C--+  
  paddle dit in  D0        5V
  paddle dah in  D1       GND
      buzzer pwm D2       3v3
         key out D3       D10 in  button 1
     i2c sda     D4        D9 in  button 2 
     i2c scl     D5        D8 in  button 3
          tx     D6        D7     rx
                 +----------+

Schematic

Bill of Materials

Part	Description	Link
U1	Seeed Studio Xiao Controller RP2040	https://www.seeedstudio.com/XIAO-RP2040-v1-0-p-5026.html
J1	3.5mm Stereo Jack	https://www.digikey.com/en/products/detail/cui-devices/SJ1-3523N/738689
J2	2.5mm Mono jack	https://www.digikey.com/en/products/detail/cui-devices/MJ1-2503A/738679
Buzz	Passive Piezo Buzzer	https://www.amazon.com/gp/product/B018I1WBNQ/
Q1	2N7000 n-channel MOSFET 60V TO92-3	https://www.digikey.com/en/products/detail/onsemi/2N7000-D74Z/3478161
C1	Capacitor ceramic 0.1uF 50V	https://www.digikey.com/en/products/detail/kemet/C315C103K5R5TA7303/3726109
S1 S2 S3	Tact switch SPST NO 6mm x 6mm	https://www.digikey.com/en/products/detail/cit-relay-and-switch/CT11025-0F160/12418891
Headers	Header female 7 position 0.1 pitch	https://www.digikey.com/en/products/detail/sullins-connector-solutions/PPTC071LFBN-RC/810146

Most of the parts are generic: I have given the links to where I got them. Note that not all audio jacks are created equal: the pin locations can vary.

Assembly

The only tricky part is soldering the castellated Xiao to the board. Here is a tutorial with video on soldering castellated parts. I think I put too much solder on the first time I tried, and filled the through holes on the Xiao. Not a real problem, but probably not best practice. Also, definitely solder the Xiao on first, especially before the headers!

Not all parts are required.

• For minimal functionality, solder on:

  • U1 Seeed Xiao controller

  • J1 3.5mm jack to Iambic key

• To have local side tone generation, add:

  • 9mm piezo buzzer (note polarity)

• To key a radio with a sinking open drain output (up to 50V), add:

  • Q1 n-channel MOSFET transistor
  • C1 0.1 ceramic capacitor (to lessen key clicks?)
  • J2 2.5mm mono jack (open drain on tip, ground on ring)

• To trigger stored messages:

  • Add S1, S2, and S3 tact switches

• To allow easy access to the Xiao pins for expansion and experimentation:

  • Add 7 position female headers

Future

Some Ideas:

• The I2C pins are available to expand to other parts, including a display or other inputs
• The Rx and Tx pins are available to expand to a (3.3V level) serial port

References

The iambic keyer state machine owes a great debt to the 1keyer project by Mark VandeWettering, and the PIK project by Owen Duffy.

Larry Kuck (WB7C) has very helpful resources at Morse Code for the Radio Amateur