I am intrigued... I have two retro pcs (486 and MMX200) and I would like to interface with both of them through just one mouse/monitor/keyboard. This switchbox off Ebay seems to be able to do the trick.
This is definitely gonna mess with video signal quality but most importantly it also messes with keyboard and keyboard controller since in disconnects them at any random points. You may get weird issues when switching from one device to the other as far as keyboard goes. Any typematic settings will reset, all the lock settings reset, and mouse will also reset to default state on each switch.
Better things use a little MCU in them that keeps track of what settings are sent to the connected devices and keep them alive for each input.
This is definitely gonna mess with video signal quality but most importantly it also messes with keyboard and keyboard controller since in disconnects them at any random points.
Thanks for the remark. I am so intrigued that this morning I pulled the plug and placed an order.
With it I ordered DIN M/M cables, VGA cables (1m and 0.5m) and RS-232 cables to go along with it.
I also thought about the issues this would cause to the keyboard and mouse - well my idea behind this is to switch between the computers before actually turning any of the on. I do not think that at any point, I would like to control both PCs simultaneously, switching between then on a whim. I just want to avoid the need of keeping shuffling the cables from one to the other, especially when the accessibility from behind of each computer is very poor.
I also realised I need to switch between audio outputs of each PC (just one set of speakers) so ordered a switch and some 3.5mm M/M cables
It is going to take a while for all the material to get here, but I intend to give you guys a report how the system works once I get it up and running.
An update (and also a report),
I got finally all the parts I have ordered for for the switch, including of course the switch itself, and proceeded with some testing - here are my findings:
Regarding video quality - as predicted, the quality of the video signal is somewhat degraded (Smearing, ghosts). I find that it is highly depentent on output resolution and refresh rate, as well as on the monitor itself.
As I ordered two VGA cables (1m and 0.5m), I find that the cable lenghts do not play any role. The VGA cables themselves however are quite thin, no ferrite cores, and presumably poorly shielded.
When switched to my Apex 486 running Win95 at 640x480 256 colours (Spea V7 Mirage ISA 2MB card), I do not notice any degradation of the image at all on either CRT (AOC Spectrum 9Glr and Samsung Syncmaster 957p).
The situation is worse when switched to my Oakmont 200MMX (Diamond Fire GL 100 Pro passed through Voodoo 2 card) - It is worse the higher the refresh rate. Output resolution and color depth do not matter. I find that it is 'almost' unnoticeable at 800x600 24bit and 70hz. I will however be getting better sheilded VGA cables to see how things improve, I think there is some wiggle room.
DIN keyboard and serial interface for mouse work perfect no trouble at all. Same with the audio switch.
What surprised me the most is that I can actually switch between the two computers on-the-fly, when both are running - it works great, but I suspect the behavior could be highly dependent on the HW configuration of the computers themselves. As luck would probably have it, my two PCs allow switching between then on-the-fly, without any error in mouse or keyboard inputs. Here is a link to a VIDEOI made showing how nicely it transitions between the two PCs.
I placed the switch box under one of the speakers - I observe no trouble with further degradation fo video quality near the speaker magnet. What is the least pleasing is the resulting cable clutter, but that is to be expected.
Overall - I am quite happy with the switch and how it works. I think it makes for a nice addition to the two-PC setup, making it nicely compact and convenient. I am also glad that I am able to switch between my two particular PCs on-the-fly without any keyboard/mouse communications errors.
It's not exactly that you can't switch computers on the fly, but the dangers of it. The keyboard port may burn down (usually they have a fuse there), when you do the switching.
You really don't want to use the switch while any of the connected computers are running. Really.
"640K ought to be enough for anybody." - And i intend to get every last bit out of it even after loading every damn driver!
It's not exactly that you can't switch computers on the fly, but the dangers of it. The keyboard port may burn down (usually they have a fuse there), when you do the switching.
You really don't want to use the switch while any of the connected computers are running. Really.
@assasincz, pins connecting in the wrong order. It's not exactly surge, but a flow of power through wrong part of circuits.
Okay I think I understand. I will try check with multimeter if something like this happens during switching, if by any chance +5V gets sent to different pins before the switching is done.
Rather than burning out the keyboard port, would not this put the load on the keyboard itself?
The problem is about pins not connecting in proper sequence. And this way, when you have let's say "wrong 3 pins" connected while other 2 are not yet, the power may already start flowing, but not in a way it has been meant.
This is also a danger of just connecting/disconnecting DIN/PS2 keyboards while computer is working. Not related exactly to your switchbox.
"640K ought to be enough for anybody." - And i intend to get every last bit out of it even after loading every damn driver!
The gist of this is, components expect to be powered via their V+ and Gnd pins before having signals traverse the data pins.
So, on a KB/mouse, you have Gnd, +5V, Data, and Clk. If Gnd happens to be the last pin switched, the KB/mouse could end up trying to return current through the Clk pin, for example, if the host is inhibiting the clock. In some cases, this is not a big deal. In others, it could mean passing tens or 100s of mA through a data pin that wasn't intended to sink/source more than ~5mA.
Or, if the power rail is switched last, the device end might shunt the idle voltage (+5V through a pull-up resistor on the host) from the Clk/Data lines through an input protection diode. Those are commonly found on digital inputs to protect the internal gates from voltages above V+ or below Gnd, like from static discharge or inductive collapse, but they aren't meant to carry much current -- at least not for long. (Now, admittedly, the delay between pins while switching shouldn't take long -- as long as the switch is healthy. But still.)
