It can be better to pay first

Paying for a good tool or a part can be a bit offputting as the initial expense seems to be much higher. However cheaping out and getting something that might not work properly will most likely be more expensive in the long run.
I have had that idea highlighted for me while I was setting up a KVM switch so that I can run both the beaglebone (Mill) and the 386 (Lathe) through the same monitor.

These are the parts I tried to use. I got the keypad, kvm and an extra VGA cable from The Junktion for $5. All of them seem to work and are in good condition and would probably work in a more normal situation.

This is the KVM switch. It's better than the last ones I had because it gets all of it's power from the computers. However it's a bit different in that it needs a set of keys to be pressed on the keyboard to change the controlling computer. I don't use scroll lock much, particularly on these computers so that won't be a problem.

The stack of adapters. The fan I had wasn't working so this was going to be fine for a test. I do have an HDMI to VGA adapter somewhere that will let me have a fan and get video out; but I can't find it at the moment so I'll make do.

And here we have the rat's nest. I don't do a lot of cable management because I am changing things so often that having a strict management system would get more in the way then a mess like this. Regarding noise and crosstalk between the cables, anything back here with a signal is shielded and the only thing with significant power other than the mains cables is the drive to the stepper motors which is reasonably heavily shielded. So I don't think noise will be a problem and I certainly haven't had any issues yet.

With everything plugged in I powered it all on and... It... didn't work. It would display the screen from the 386 but I could not change it to display from the beaglebone. I think what has happenend is the KVM switch is expecting to be plugged into PS/2 ports (That's why it has them I guess) but I am plugging it through an adapter into an old style keyboard connector and that's it. No mice or keyboard from the Beaglebone.

I think this is causing it to run out of power and just not work properly.

To fix this I am doing what I should have done in the first place and buying a cheapy from ebay that is completely passive. From the picture of it's guts I saw it is very basic which will be perfect for this as then there is less chance it will not work.

So sometimes it pays to just buy the right thing in the first place. But for a hobby, while it can be frustrating and demoralizing it usually isn't too bad. In a business situation however it can cause major problems.

Cheers,
Rex