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K2 OptoCAT - The safe RS232 CAT interface and PA buffer for Elecraft K2

Here is a simple interface for Elecraft K2 with KIO2 and a buffer to switch on TX an external Power Amplifier (PA).

Like all my interfaces, also this one is optocoupled to electrically isolate the rig from the PC.

I choose two single, easy to find, optocouplers 4N25, but, if you want, you can use one double optocoupler TLP504A or CNY74-2.

To power the circuit on the PC side, I use the DTR and RTS signals of the PC: with all the software I tested, these pins are at +12V

I built mine using the ugly construction on a little unetched piece of copper-clad circuit board that fit in a very little plastic box, as you can see in these pictures (click to enlarge the pictures).

I had in my junk box two toroids that I used, just to stop better any RFI...

The interface is tested and perfectly working at 4800 baud with CT9, Writelog and DX-Base; I think that it will work with any software that don't needs the handshake to the radio with RTS and CTS.

My "radio" PC is a PII 500MHz on an QDI Advance 9 motherboard but the interface worked fine also connected to the "main" PC, a PIII 933MHz (Intel 815 chipset) and an IBM PII 300MHz Notebook.

Ciao, 73 and good work

Guido, ik2bcp / iu2r / ab9dg

Any question and/or comment to ik2bcp AT