First post, be nice . Ok, so I was sitting in computer science today brainstorming ideas on how to raise money for a USB KVM when I had an idea... I could try my hand at my own. I figured since the VGA cable only has 10 necessary wires, HSync, VSync, Red, Green, and Blue. Each cable has a positive and negative. Riiight? So I came up with the idea of simply having a setup of 5 relays [ one on each + line ] for each VGA signal [ there are only two ] then power each set of relays seperately to turn each signal on and off. Then I wondered if this was at all do-able, so I came here to what seems to me to be the Mensa of computer-related things.
Welcome to the forums. Sure it is do-able. You can get Four-pole Double Throw (4PDT) relays that are made for cars, that would greatly cut your number of relays down. (Two 4PDT, and a DPDT) Or use three 4PDT's and have two extra pins that can switch. As far as USB, another two 4PDT would switch a USB jack each. Or mabye only on if you just switch the data lines (not recommended)
Welcome aboard! the idea will work.. i guess... but i think it would be more practical to get a 10 way switch... cinda' har to find, but still cheaper and simpler than 10 relays..
Thankz Zap, btw I got the idea from your LAN Case Just data line switching for USB not recommended? Nuts. Oh well, that's just another relay. Is this how a "real" KVM works? Or is there some complicated signal-enhancing I'm unaware of? Smilodon, a ten way switch?! Wow. Off to google now.
A real KVM uses solid state chips to route the signals. But very large (8 pc's or more) KVMs use relays.
If you end up making it... make sure you use a decent sized wire... a lot of KVM's I have used use thin wires which causes a lot of ghosting on the screen (especially at higher res)
Thick wire? Well, I'm takin' the maximum the crimp pins will take which is sometimes 26 and sometimes 22 guage wire. I've also got ferrite beads on order from All Electronics.
VGA signals...no problem. USB relay? Dunno about that. Ive recently been looking at the USB2.0 protocols, and there is something in there about the host deliberately turning off the device bus if it cant talk to it. This could be for totally unrelated device descriptors though. Keyboard and mice USB use the interupt interface. They are polled every 1 to 255 msec. Say you turn on PC A, the KVM is routed to that PC, it will recognize the USB devices right away. But what if the KVM was not routed to that PC? Would it be able to pickup the mouse and keyboard later, after the KVM switches over? Just some thoughts to throw in the mix.
As far as I know both PCs [ one a Windows/Linux box and the other a Mac ] have no problem booting sans-keyboard & mouse. If it becomes a problem later the case I'll be building all of this will have the PS/2 ports exposed for the PC. But I know for a fact that the Mac will take a mouse & keyboard at any point in time.
USB mice on my PC are fine... duno about a usb keyboard though And as far as ps/2 goes for pc, the mouse muct be connected at bootup and disconnecting the keyboard will sometimes crash the computer. Hope that helps EDIT: Actually, I have a one of those intel mouse/keyboard/gamepad combo things I don't use anymore, and it uses usb... Never had any porblems booting up without it installed or unplugging it and plugging it in again. I didn't even need the drivers to use the keyboard and mouse, though the gamepad did need its drivers.
Ok, so I ordered 12 DPDT relays. I looked at the car relays Zap mentioned and figured they weren't worth the extra cost, seeing as how these will just be mounted underneath the desk in a box anyway. Thanks all of you for your help, and as it turns out I can hot-plug my USB keyboard and mouse on both my PC and Mac [ just double checked mid-way through this post ]. I'll update with how this goes after I get all my parts and finish it up ...should be in a couple of weeks, seein' as how not only do I have summer school, I also used standard shipping 'cause I'm a cheapie like that
