Never connect your Arduino pins directly to a radio's keying jack. Vintage rigs carry lethal voltages, and even modern rigs can experience ground loops. Use an optoisolator (such as the 4N25 or PC817) to completely isolate the microcontroller from the transceiver.
Block B: Transmitter Keying Interface (The Optocoupler Approach)
Unlike commercial products, repacks are community efforts. Here are the most reliable sources as of 2025. k3ng keyer schematic repack
): If you want everything —LCD displays, rotary encoders, and multi-rig control—go with the Mega. It has ample pins and RAM to handle the full suite of "Squirrel" features without breaking a sweat. 2. Streamlining the Schematic
The K3NG Keyer project is an incredibly rewarding endeavor for any ham radio operator. By using this consolidated "schematic repack," you can streamline the building process, moving from a pile of components to a fully functional, high-performance CW keyer. Always refer to the K3NG Github Wiki for the latest updates and detailed documentation. Never connect your Arduino pins directly to a
Pin D12 connects through a 220-ohm resistor to a second optocoupler (PC817) following the exact same architecture as the Key Line.
with standard speaker outputs.
For a new ham, trying to wire a K3NG keyer can feel like solving a puzzle where the pieces are in different rooms. A typical problem:
Keying line (via Transistor to Transmitter), Sidetone (Piezo buzzer). It has ample pins and RAM to handle
Memory channels, contest serial numbers, adjustable speed/weighting, WinKey emulation, PS2 keyboard support, LCD display, and CLI management.
Have you created or used a K3NG keyer schematic repack? Share your experience and links in the comments or on the K3NG software discussion group. Together, we can repack the future of open-source keying.