Build a Computer to CW Interface

Using a  well-known circuit, I show you how to build a simple computer interface so  your logging software can send CW through your radio.

The logging software simulates someone using a straight key.  It changes the voltage on an RS-232 pin and the electronic circuit uses a transistor as a switch, grounding the lines as though someone grounded the contacts of a straight key.

This interface will let you work a contest or pile-up using your logging software – without having to use a key or paddle.

The circuit diagram:

N3FJP website:

Tripp-Lite USB to Serial Converter: See it on

6 thoughts on “Build a Computer to CW Interface”

  1. Hey Cliff. I know this video was 6 years ago but I have a few questions about the interface. I know you are probably busy so any help you can give would be appreciated.

    I am trying to setup an old Swan radio for CW. The problem is I don’t know morse code and even if I did, I can’t hear well enough to decode. Question: Does this interface (with the software) decode incoming CW? Also, have you upgraded the interface with the FTDI board someone mentioned in the comments? With an older radio, is more than the connection to the key jack required?

    Again, I know you must stay very busy but, I was hoping that you could answer my questions before I try to make the interface and it not work the way I hope it does.

    Thank you!!!

    1. Bobby, this interface will NOT help you to decode CW. It is simply a circuit that will allow your computer to emulate a straight key in order for the computer to send CW. It’s sort of like an electronic ghost sitting at your straight key, pushing down on the lever to close the electrical contacts for you. Software controls when the contact is closed and for how long. – Cliff

Leave a Reply

Your email address will not be published. Required fields are marked *