K3ng Keyer Schematic [upd] Here

So download the schematic, heat up your soldering iron, and get on the air. 73, and may your dots be perfectly timed.

For high-voltage tube transmitters (e.g., Johnson Ranger), you cannot use a 2N2222. The schematic allows for a 4N25 optoisolator . You bridge the Arduino side with a 330Ω resistor, and the transistor side connects directly to the tube rig's 150V key line.

These are wired as digital inputs with internal or external pull-down/up resistors. Usually, pressing the button connects the pin to ground (active low).

: Often includes a "Command" button to enter programming mode via the paddles. Advanced Hardware Options