A modification of the K1EL WK3 WinKeyer USB-SMT Kit is shown.
Adding an insulated 3.5 mm stereo jack socket
(Multicomp-pro No. MJ-073H, just below the "PADDLE" input stereo jack socket)
allows to get a square-wave side tone audio signal out of the WinKeyer.
The use of an insulated socket preserves K1EL's well thought out system
to avoid ground loops in the WinKeyer.
(Keep in mind however, that the SP1 "-" PCB-pad is connected to the MJ-073H shield. An audio coupling transformer may be used to achieve isolation between the ground of an external circuit (connected to the MJ-073H socket) and the internal SP1 "-" PCB-pad of the WinKeyer.)
The 10nF capacitors shown in the schematic are ceramic, the 1µF capacitors are of the film/foil type. The 180 Ohm resistor sets the output amplitude of the circuit and may be replaced by a value which fits the needs of the individual application. The parts are soldered to a prototype PCB stripboard. This board is fixed to the bottom of the WinKeyer's case by a Velcro tape close to the battery holder. For my setup the output of this circuit is connected to the Line In input of a consumer sound card (input impedance of approximately 27 kOhm) and a 180 Ohm resistor to set the output amplitude proved to be well suited. Parameters of the WinKeyer 3.1 CW Processor/Keyer IC are found in its data sheet .