Having been disappointed with the ability of my K3 to readily provide outputs to switch VHF/UHF transverters I decided I needed a solution.
Initially I used some logic ICs to decode the band data on the rear panel ACC connector, but having to reconfigure the interface every time I added or deleted a band was a right pain. This was described at http://g4fre.com/k3vhf.pdf
Next I decided to use a PIC to do the decoding as it was easier to reprogramme a PIC chip than it was to redo the logic circuits. This decoded just 4 bands as it was intended for 4 bands HF, 6m, 2m and 70cm. This was described at http://g4fre.com/K3_PTT_sw.htm
Next I designed a circuit to decode the RS232 signals also available from the back panel. This looks at the 38400 Baud RS232 data and provides a 1 of 8 band output and a corresponding 1 of 8 PTT signal. It was designed for the 8 bands 144,432,23cm, 13cm, 9cm, 6cm 3cm and 1.2cm. This was written up at http://g4fre.com/K3_RS232_sw.htm . This worked fine for my station in the USA. However I received a request to make it decode the 8 bands 4m, 2m 70cm, 23cm, 13cm, 9cm, 6cm and 3cm for use in the UK. So today I modified the code and tested it out and it works fine. This version is at http://g4fre.com/K3_RS232_UK.htm
I also tested it out on my Elecraft KX3. It worked fine, all we need now is for Wayne to write the software to support transverter mode in the KX3