In September 2004, I set up an Echolink link to cover the East Mesa area. I used my Kenwood TS-790 as the radio, and a surplus audio mixer for the interface. But I still needed a better way than vox to key the radio. So I built a simple 1-transistor level converter that takes the RTS line from my computer's serial port, and converts it down to TTL in the correct polarity to key the TS-790. I started with making a hole in the case to accommodate a full size DIN connector to go to the 790.
Next, I drilled and filed out a hole to put a 9-pin rs-232 connector on the other end.
Next, a db-9 connector was mounted on the case.
Then I built the simple circuit on a piece of perfboard.
And finally, the wiring was completed to the circuit. On-the air testing showed no problems, so it is still in use today.