On my web site (see below), in the 'Beacons' section, you will find PCBCN.zip which is a simple Windoze utility that activates a COM port at regular intervals   Specify repeat interval and offset in minutes, and the Tx ON time in seconds, and it will set the RTS and DTR lines of your specified COM port for the duration when the appropriate interval arrives.  That's all, no CW messages, no bells, no whistles, no warranty!

 

.. and its entirely up to you to somehow keep the PC clock accurate enough!