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#1 2015-08-31 20:30:39

markyb
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From: Bedford, OH USA (216)
Registered: 2014-05-16
Posts: 182
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Theorycrafting: Video switchbox = easy to find ADB KVM?

http://www.amazon.com/Recoton-SVS1000-S … B000031WCH

Would one of these boxes or a similar cheaper one, work as an ADB switch? I use some S-video cables for my keyboards, figured this would pass the signal through the same as long as the connections are 1:1. Anyone ever try it?


http://markyb.applefool.com for a list of my computers, my blog, and some random resources.

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#2 2015-08-31 21:27:34

Eudimorphodon
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Registered: 2014-09-02
Posts: 525

Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

Well, the issue there is that ADB isn't really supposed to be hotplugged, and that's essentially what you'd be doing when using this thing. There is the potential for both software issues and hardware damage from doing so.


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#3 2015-08-31 22:03:59

jt
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From: Bermuda Triangle, NC USA
Registered: 2014-05-21
Posts: 1,407

Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

I've got a pair of KVM solutions that are Macintosh specific.

One's a four-way mechanical switch (I'll peek inside, always wondered if there was the equivalent of KM emulation in there) and there are sometimes problems with the mouse, but a utility called ADB Reset kept on the desktop to run via the desktop "Command Line" fixes that issue nicely. Never burned anything up and I used it a LOT back in the ADB day. I still run the Apple Display Unit off it with four Power/PhoneNet/10bT/VGA/ADB umbilicals I can hook up wherever I choose.

The other is an OmniView Macintosh Converter/two-way PS/2 switch combo (bought a four-way box as well) which is an electronically switched setup for running one Mac and PC off PS/2 peripherals.  I've attached the four-way mechanical oox up to the converter's inputs with zero complications other than the DA not getting along well at all with either of my ADB converters.

Pet project: I've got electrically switched PS/2 switchboxes, just need to get S-Video connectors to terminate (only) the Mac side of the switchbox cables AFAIK.

My understanding is that plugging hot is a lot more problematic than rotary switching and electronic (TTL level) switching would be less problematic that that.

PS/2 KVM boxes used to be dirt cheap on eBay, are they still around? I'd think USB KVM switches should work as well with the S-Video hack.

Dunno, no electron pusher here, I just do electron plumbing. :-/

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#4 2015-08-31 22:13:01

Eudimorphodon
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Registered: 2014-09-02
Posts: 525

Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

I'd be willing to bet that along with all those regular switchboxes JT has at least one Cinco MIDI Organizer.


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#5 2015-08-31 22:27:11

markyb
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From: Bedford, OH USA (216)
Registered: 2014-05-16
Posts: 182
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Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

Well I suppose the hot plugging issue would be solved by not running more than one machine at once? I don't have the wattage to do so anyway, so it's merely saving the reach-around to move the cable between Macs.

I haven't thought about making adapters, I do have a USB KVM around here somewhere.


http://markyb.applefool.com for a list of my computers, my blog, and some random resources.

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#6 2015-08-31 22:42:06

Eudimorphodon
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Registered: 2014-09-02
Posts: 525

Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

One big thing I'd be concerned about is in the case of a switchbox meant for AV use is that the box may well have "common" lines between ports that aren't switched, IE, like grounds. (In fact, one of the reviews of that box said they'd seen bad crosstalk and noise added to the signal because of that.) If you ended up shorting the 5v of two machines together, for instance, you could kill them both. Remember, the 5v line is actually live *all the time* in ADB, that's how the keyboard power button works.

As to the idea of wiring up socket adapters to use a "soft-switching" PS/2 or USB switchbox for ADB, offhand that sounds to me like a complete and utter no-go. I haven't seen an "actively switched" KVM in... forever, that didn't have some rudimentary logic on it that let it snoop keyboard presses and interpret some key combination as a console switch command. (And said logic is going to care, a lot, what protocol you're running through it.) An electronic switch that is literally just a switch still would be buffering the pins through some logic, and it's going to care if the grounds are high level vs. grounds. (unless, perhaps, it's using relays?) So, I dunno, maaaaaybe you could make it work if, again, it's a *completely dumb* switch, but... it's probably a smarter idea to hit eBay for a proper ADB kvm.

Last edited by Eudimorphodon (2015-08-31 22:43:06)


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#7 2015-09-01 01:33:14

ClassicHasClass
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From: Electron Alley
Registered: 2014-05-26
Posts: 1,099
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Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

And what Eudi was concerned about is exactly right: every S-video switcher I tried to use as an ADB switcher had a common ground. It didn't work.

So I'm using a dedicated ADB KVM.

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#8 2015-09-01 03:45:34

jt
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From: Bermuda Triangle, NC USA
Registered: 2014-05-21
Posts: 1,407

Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

Hrmmm? Somewhere over yonder, there's a thread or two about turning a simple DB-25 Switchbox (all lines switched) into the ultimate Mac I/O Signal KVM switchbox. Gotta look to see it it's on iFrog.

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#9 2015-09-01 04:15:13

LCGuy
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From: Sydney, Australia
Registered: 2014-05-13
Posts: 815

Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

Assuming that this is the same kind of deal as the AV switchboxes that we have here in all the cheap discount stores, its certainly not something you'd want to use with ADB given that its basically the same as hot-plugging the devices, as Eudi mentioned.

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#10 2015-09-01 05:30:31

jt
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From: Bermuda Triangle, NC USA
Registered: 2014-05-21
Posts: 1,407

Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

I've gotta open up my Mechanical ADB KVM to see what's inside. I'm pretty sure hot plugging is a lot more worrisome than rotary switching when it comes to electrical characteristics of the mechanical connection types  .  .  .  but I've been known to be wrong  .  .  .  quite a lot actually. tongue


@ Eudi: WTF is that thing in the video? (Looks like a commercial parody on SNL?)

edit: one of my crazier notions was to do crossover switching in DIP TTL so that all the "switchboxed" Macs would always be connected to a controller card from an AppleDesign with a gummed up ADB Mouse board attached to that. Sort of Keyboard/Mouse emulation in the KVM by substitution?

Last edited by jt (2015-09-01 15:46:50)

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#11 2015-09-01 15:44:33

jt
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From: Bermuda Triangle, NC USA
Registered: 2014-05-21
Posts: 1,407

Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

Just took my Video ADB switchbox apart and it's an almost pure mechanical rotary switch design. It only has three umbilicals to unhook, thought it was four, but I haven't actually used more than one or two of the Apple Display Macs while on the display in a very long time. They're all hangar queens that come off the shelf and onto the workbench for evil experimentation playtime. I still haven't hooked up more than one umbilical of the switchbox setup since I moved six years ago.

Anyway, the only electronics are the resistors(?) shorting two pins on the da-19 Video input CONNECTORSs. First approximation is that they're for VGA conversion. The box has VGA and Mac Video outputs wired in series. The case sticker says:

"ON-THE-FLY" RESOLUTION
FOR VGA/MAC MONITORS
WORKS WITH CENTRIES, (TAIWANglish)
QUADRAS AND POWERMACS
UNDER SYSTEM 7.0


CHC, is your dedicated ADB KVM a rotary switch or TTL gate based design?

I'd say we're good to go with rewiring any Rotary Switched PS/2 KVM for S-Video(ADB) and DIN-8(serial) panel connectors with each VGA HD-15 input converted at the Mac's backplane. My box has Mac DA-19 inputs, but that's not an option using an off the shield PS/2 HD-15 VGA KVM.

Last edited by jt (2015-09-01 16:00:21)

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#12 2015-09-01 17:50:28

Eudimorphodon
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Registered: 2014-09-02
Posts: 525

Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

jt wrote:

Anyway, the only electronics are the resistors(?) shorting two pins on the da-19 Video input CONNECTORSs. First approximation is that they're for VGA conversion. The box has VGA and Mac Video outputs wired in series. The case sticker says:

"ON-THE-FLY" RESOLUTION
FOR VGA/MAC MONITORS
WORKS WITH CENTRIES, (TAIWANglish)
QUADRAS AND POWERMACS
UNDER SYSTEM 7.0

So, my guess is those resistors are there to make the Mac that's "not connected" to the monitor think it is, because a lot of Macs disable the video output if they don't detect any sort of monitor when they're powered on.

... I also vaguely sort of wonder if it might be doing something skanky with the monitor ID lines, particularly the DDC lines. Are you positive those are resistors and not diodes? In theory at least I think you *might* be able to let both machines see the DDC info broadcasts if you were clever, which would explain the whole "ON-THE-FLY" RESOLUTION thing.


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#13 2015-09-01 17:54:17

Eudimorphodon
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Registered: 2014-09-02
Posts: 525

Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

jt wrote:

@ Eudi: WTF is that thing in the video? (Looks like a commercial parody on SNL?)

"Tim and Eric Awesome Show, Great Job!". It's... a thing that exists THAT'S PERFECT FOR THROWING AWAY!


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#14 2015-09-02 17:04:58

jt
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From: Bermuda Triangle, NC USA
Registered: 2014-05-21
Posts: 1,407

Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

Just opened my KVM labeled MANHATTAN "Data transfer switch" to check it out. Buzzing lines as time allows, but initial results are very promising, there's no way in the world that these can't be converted to at least VGA/ADB switchboxes. I can't imagine why a single PS/2 's DIN-6+clean ground can't be converted to ADB

All four PS/2 signals are switched along with both unimplemented pin's connections and a seventh for shell ground line (isolated from panel ground?)


ISTR that MANHATTAN (a small peripheral/cable importer/mfr. in Brooklyn with a booth at local shows back in the day) became cablesonline  .  .  .

.  .  .  and voila!! smile Simplified version still available:  Single PS/2 KV Implementation

$15.99 price point is hard to beat, no serial switching feature available though. hmm  Mine has both PS/2 ports

Last edited by jt (2015-09-02 17:13:31)

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#15 2015-09-02 18:05:26

Eudimorphodon
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Registered: 2014-09-02
Posts: 525

Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

Technically PS/2 isn't supposed to be hotplugged either. The fact that, yes, people did make crude switchboxes that did it anyway doesn't exactly undo that objection. It is true that you're probably *less likely* to physically blow something up with a clean switch throw than by pulling and reseating a cable (IE, the possibility exists of shorting the wrong pins together, etc, when you're fumbling with a plug) but it's still not really kosher. I do remember using one of those crude turn-the-knob keyboard switches (with AT plugs, not PS/2, no less) back in the day and you were pretty much throwing a 20-sider every time you did it. Roll a fumble and you'll get a dead/garbage keyboard and probably have to hit the RESET switch.


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#16 2015-09-02 18:17:36

volvo242gt
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From: Duvall, WA
Registered: 2014-05-22
Posts: 406
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Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

IIRC, coiled keyboard cables aren't that expensive.  Just hook one up to each Mac (and Apple IIgs, if one is handy), then put a small tag identifying which computer it is.  When you're ready to use a certain machine, plug the keyboard and mouse into its cable, then switch the monitor to that machine and hit the power key.  Cheaper than an ADB KVM.  A little messier, too, but no reach-around needed.

-J


modern: Mac Pro 2.8GHz 8-core 6GB/500G/DVD-RW, A1150 MBP 2GHz CD, 2GB/80G/DVD-RW
Pre-Mac: ][+, //e
other: iPhone 6s 128GB Space Gray

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#17 2015-09-02 20:44:20

jt
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From: Bermuda Triangle, NC USA
Registered: 2014-05-21
Posts: 1,407

Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

Straight S-Video cables are a lot more available and much less expensive than coiled ADB.

S-Video cable = fabulous shielded ADB cable
ADB Cable = horrendous unshielded S-Video cable

I used my dedicated, rotary-switched Mac ADB KVM for many years of "hot plugging" without incident.

I've never read the ADB spec, has anyone else actually seen the hardware restriction/CAUTION! DAMAGE WILL ENSUE! spec for ADB. While it's a given that it's not hot pluggable from a signal standpoint (my need to use ADB Reset to de-zombify my mouse on a semi-regular basis proves that point) I'm not convinced that the problem lies in hardware.

Common knowledge/"received wisdom" are ALWAYS suspect in my experience. Until I see the hardware spec limitation in Apple's documentation, equipment damage remains an open question, much rumored about over many, many years, but undocumented. The rumor's cautionary, unlike the almost universally accepted "received WISDOM" that it's OK to run a Portable using a Series 100 AC Adapter.

YMMV, but I definitely wanna see it in the specs to be sure.

Anybody got Apple's Apple's developer kit documentation for ADB licensees handy?

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#18 2015-09-02 21:35:16

bbraun
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Registered: 2014-05-29
Posts: 1,064
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Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

The ADB protocol is kinda sorta capable of hot swapping.  I say kinda sorta because the device can be assigned a specific address, and that address will get lost when the device loses power.  However, keyboards and mice generally live at addresses 2 and 3 respectively, and although they will temporarily be reassigned a different address on host startup, the purpose of that is to detect multiple devices of the same type.  So if you have 2 mice attached to the system, they'll both have address 3 when they are powered on.  The devices can detect collisions on the bus, and when the host tells them to change addresses, only one will do that because they can tell if their response is colliding, they'll go through a bus arbitration phase, and only one responds and will get the new address.  The other(s) will stay at the same address, and if there's more devices, the process repeats until there's nobody left at the starting address anymore.  Generally, there's only one mouse and one keyboard, and the system reassigns them from the temporary address back to their original address, which means it'll all be ok.
Additionally, even if a new device is added to the bus at a completely different address, if it wants to talk, it can send an /SRQ signal to let the host know there's someone that wants to talk.
So generally, for keyboards and mice, it'll work out at the protocol level if all the devices behave properly.  Exceptions can be for special devices that require some host side initialization that won't happen or gets lost if the device is unplugged.

The problem is electrical/mechanical.  The biggest problem is the ADB signal (and POWER.ON signal on soft power machines) goes directly to the ADB transceiver (one of the VIAs on earlier machines, Egret on later ones, etc.) without any sort of ESD protection.  Additionally, power is flowing all over the place with the ADB connector, since there's the +5V line which is on whenever the machine is on, the POWER.ON signal is +5V all the time even when powered off on soft power machines, and the ADB signal is +5V when idle, which is most of the time.  The ADB connector doesn't have staggered pins to ensure ground gets connected first, so you can be getting +5V on 3 of the 4 pins, without a ground, which can cause problems.

But really, the biggest problem is zero protection of the ADB transceiver.  It really is just the pin on the chip to the ADB connector.  You run the risk of asploding whatever does ADB on the machine you're connecting to, which would be a real bummer.
Watch The Shocking Truth training video on ESD for some educational fun on the dangers of ESD.

That said, I'm pretty sure all of us have hot plugged the ADB connector at one time or another, and chances are, nothing (noticeable) happened.  Just be aware that there is an actual real possibility of damage.

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#19 2015-09-02 23:32:26

ClassicHasClass
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From: Electron Alley
Registered: 2014-05-26
Posts: 1,099
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Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

My ADB switcher is just a button box, so I imagine it's a hard connect-disconnect inside, nothing soft.

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#20 2015-09-03 04:08:47

jt
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From: Bermuda Triangle, NC USA
Registered: 2014-05-21
Posts: 1,407

Re: Theorycrafting: Video switchbox = easy to find ADB KVM?

Strange mix of information there. Watched 1.5 of the set of four videos. It seems to me that there's a much higher probability of ESD borkage to the ADB controllers from plugging and unplugging the cable connectors cold than from rotary switching the signal lines.

Just looking at the wiring inside my PS/2 KVM, the seventh "shell ground" lines could be snipped at the switch and soldered together. That would keep every piece of equipment hooked up to the switched "ADB" network at the same potential level(?) at all times, with no chance of ESD damage at all in that case?

There's still discrete signal ground and power to worry about though  .  .  .

Do zener diodes dump overvoltages to ground fast enough to protect the controller ICs from the kind of bad juju under discussion?

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