So about a year ago I picked up an Aten CS1734B KVM switch out of an old parts bin with all the cables (sans one) attached, and thought it'd be dead. Got home, plugged it in, nope, it works fine. I just scored nearly $200 worth of KVM for nothing. Sick! However, the keyboard I use mostly with it, my Logitech K400, doesn't work with it properly. This may have been fixed with a firmware update, and using a standard keyboard, I know that the firmware on this particular KVM is quite a few versions out of date. I need a firmware upgrade cable. Here's the problem. There are actually two hardware revisions of this KVM switch. One which uses a bastardized RJ-11/12 cable, which you can find aftermarket cables for, I think I even found a pinout somewhere (this was months ago), and one which uses a bastardized 3.5mm TRRS (I believe) headphone jack. Guess which one I've got. I emailed Aten asking if they provided cables aftermarket, and the response was "I'll get our supplier to contact you". Never thought I'd see the day until a week later when the supplier emails me. "We don't normally do this, but I can sell you a cable for $20" or $25 or whatever it was. $20 for a cable I'm only going to use once, maybe twice? Felt like telling him to take a running jump. ANYWAY on to the question. Is there a way I can determine the pinout of the headphone jack so I can make my own cable? I know it talks RS-232, but that's about it. I think it has 4 conductors, 5 if you count the grounding plane. Can I hook a TRRS headphone cable up to a breadboard and have the breadboard also hook up with the COM port on the computer? More importantly, can I do this without killing something? Is the worst thing that can happen "it won't work until you find the right pinout?" I can take the KVM apart for photos if anyone needs a reference to what I'm talking about, fortunately this KVM is easy to pull apart (and put back together). Cheers.