Push-To-Talk Foot Switch Adapter for KX3

Recently, I picked up an inexpensive BM-800 condenser microphone for my KX3. It works beautifully. However… I don’t like running in VOX. I get too many interruptions. So I need a PTT solution other than using the PTT button on the KX3. I’ve had this Heil FS-3 foot switch sitting in its box for over a year, just waiting and waiting for this moment to come:



The foot switch isn’t anything fancy, it just shorts to two conductors on the plug when the switch is pressed. It’s a good quality switch though, I do recommend it.

What I wanted to do was create an adapter so that I could use the foot switch to trigger PTT on the BM-800 microphone. To figure out how to do this I decided to look at the schematic for the Elecrtaft MH-3 hand microphone:



According to the schematic, the shield is the ground, the tip is the mic audio, and the rings (R1 and R2) are what control PTT. If I just shorted R1 and R2, that would cause the KX3 to TX. I didn’t care about band up and band down, so it seemed simple enough. Here’s what I came up with for a design:




I felt this was a good design to fit all situations, but I wanted to check and see what the wiring was like specifically on the cable from the BM-800. So I opened up the XLR end to see how it was wired:



As you can see here, the two pins show are wired together, and the ground is wired separately. Some testing with my Fluke made it clear that both the tip and the ring were wired together. So my design was good, and there was no need to connect the ring to anything.

I assembled the following parts:

And this is what came out as a result:

photo12Here’s a good look at the 1/4″ jack wiring (foot switch)

photo11Here’s a good look at the stereo jack wiring (BM-800)

photo10Here’s a good look at the 1/8″ 4-conductor jack (KX3)

photo14The closed container, the foot switch jack on the left and the KX3 jack on the right

photo13The closed container, the BM-800 jack on the left and the foot switch jack on the right

Does it work? You bet it does! I’ll post more pictures later of the complete setup when I get the boom and pop screen installed!

Posted in KX3

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