USB CW Keying Interface

The current-limiting resistors can have a value up to 1k.
The FT232 USB-TTL converter is powered from the USB port, i.e. from the computer.
Optionally, two indicator LEDs could be added in series with the optocoupler LEDs, but then the resistors should be 270 Ω.

I use one of these USB-to-TTL converters.
The jumper is set to ‘5 V’.

A cable clamp holds the cable connector in place. That ain’t going nowhere. 🙂
The outputs are (opto)isolated from the computer. The enclosure is connected to the ground on the radio side only.

The interface has been successfully tested with Win-Test and DXLog under Windows 10 and Windows 7 (both 32-bit and 64-bit), and with N1MM under Windows 10. It should also work with any other logging program that (as per the de facto standard) uses the pins/lines RTS and DTR to control the transmitter.

The red light of the power LED shines out of the cable opening.
The case is from Aliexpress and measures 80 x 50 x 20 mm, $2 each.

The FTDI drivers are easily available and often already present in the OS. The interface will present itself to the user as a new COM port. In Device Manager go to this new COM port Properties->Port Settings->Advanced. Then in the Miscellaneous Options section (bottom right) uncheck Serial Enumerator and check Disable Modem Ctrl at Startup. That will prevent the interface from keying/unkeying the radio for a moment as it boots up.

P.S.
I also tried to use a converter board based on the CH343G chip, but I couldn’t get the driver to work properly. The RTS pin did work correctly on all the Windows versions, but the DTR pin responded intermittently at best. Maybe there is a workaround or a new version of the driver will solve the problem. Anyway, I gave up quickly and went back to the FTDI boards that worked with no issues.

New and (very slightly) improved: the USB keying interface v2.0: