Serial PTT Circuit

In the spring of 2009 I purchased N8LP's LP-Pan Panadapter and needed a better computer in order to run the SDR programs like NaP3 which could utilize that hardware.  I decided I would build myself a speedy computer to do just that.  I researched and purchased all the parts necessary and then on July 3rd I broke my right leg really bad.  I was in a wheelchair for 4 months after spending about 16 days in the hospital.  During all this the computer parts just got shoved under the bench and left there for about 7 years!  Recently a friend put it all together and I have a nice (essentially new) XP Pro SP3 computer with 4 GB of RAM. Since XP is really not supported anymore, I decided to utilize this computer for my digital operations thus keeping those separate from the computer I use for Internet surfing, email, etc.

Serial PTT Circuit

In setting up that newly-built computer to do this, I find that I need some way to allow that computer to key the PTT of the Elecraft K3S.  My normal station setup has the microKEYER II connected to the K3S and the Windows 7 computer.  So, I purchased a 2-port Serial PCI controller card and installed it in the XP computer.  That gives me two COM ports that I can use for various things - one of which will be to key the Footswitch input of the microKEYER II.  This will cause the K3S to go into transmit when the WSJT software wants it to transmit.

Completed Wiring of the Circuit

A little searching on the Internet found a suitable circuit (shown on the left) and I only needed to acquire a couple of diodes and a transistor to build it.  Luckily there is still a Radio Shack outlet in Kanawha City and they had an MPS2222A transistor and a pair of 1N4001 diodes in stock.  I already had the resistor, the DB-9 plug, and the cable in my junk box.

It did not take much time to wire up the parts and you can see the completed Serial PTT circuit on the right (click on any image to see it larger.)  I chose to use the RTS line but I could have used DTR just as easily.  I only need to tell the WSJT software the COM Port number and click on the RTS button to allow the software to communicate with the microKEYER II.

A quick check of the circuit by telling the WSJT program which COM port to use and plugging the cable into the Footswitch input of the microKEYER II and, VOILA!  I can now key the K3S from the newly-built XP Pro computer - SUCCESS!