Keyboard extension cable

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Quzar
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Keyboard extension cable

Post by Quzar » Wed Oct 14, 2009 5:56 am

I'm thinking of moving my computer across my room to be part of my entertainment center. I already have a video cable covering the distance which will now be used for my primary monitor and have plenty of long ethernet cable that can go the distance but am missing one component I'm unwilling to sacrifice, my model M.

What I was thinking of doing was rigging up two adapters to be able to use an ethernet cable (basically free to me) to extend it. The only real question I have is if this will work and what might the max distance be? I planned on using two wires in the ethernet cable per PS/2 pin (the Model M only uses 4 of the PS/2 pins), which could possibly help alleviate EMI or transmission issues; are there any patterns (11223344 or 12341234 etc) that would prove to be more useful or successful? If needed I could even add a power source to the keyboard side or such.

Thanks for any relevant information. If you have any suggestions for solutions to using my keyboard across the room (spare parts style) I'd love to hear those too.

Just occurred to me: would it be possible to use a similar setup to extend a USB cable? I could just put a usb hub on the other end and that would be much more useful.
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Re: Keyboard extension cable

Post by Ex-Cyber » Wed Oct 14, 2009 8:10 am

Quzar wrote:What I was thinking of doing was rigging up two adapters to be able to use an ethernet cable (basically free to me) to extend it. The only real question I have is if this will work and what might the max distance be? I planned on using two wires in the ethernet cable per PS/2 pin (the Model M only uses 4 of the PS/2 pins), which could possibly help alleviate EMI or transmission issues; are there any patterns (11223344 or 12341234 etc) that would prove to be more useful or successful? If needed I could even add a power source to the keyboard side or such.
Adding power to the keyboard side only saves one pin, but it might be necessary to avoid voltage drop; I don't know how big of a load a Model M would be. The important thing in the wiring pattern is just to make sure that one wire in each pair is grounded; the correspondence of pair<->signal should be irrelevant aside from whatever makes it convenient for you to wire. I have successfully used a PS/2 extension cable with my Unicomp Customizer 104 PS/2, which is supposed to be highly derivative of the Model M design in most respects, so I don't think it's super-sensitive to the cable length (although the extension cable was only 6 feet or so). I used to have another keyboard that couldn't deal with the extension cable.
Just occurred to me: would it be possible to use a similar setup to extend a USB cable? I could just put a usb hub on the other end and that would be much more useful.
You could try it, but it would likely run out-of-spec in some way (slew rate, noise, and/or propagation delay). In that respect, you'd be much better off chaining a couple of small hubs together. IIRC, USB allows for a cascade of 6 hubs maximum, which is imposed by the maximum overall propagation delay; keep in mind that some devices have internal hubs that would count toward this limit. That said, I can't say that it definitely wouldn't work.
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Re: Keyboard extension cable

Post by Zealous zerotype » Wed Oct 14, 2009 9:08 pm

http://computers.become.com/shop?&bskui ... 0&nofilter
Looks like it is possible, I don't see why the ethernet cable would not work (aslong as it is insulated well enough)
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Re: Keyboard extension cable

Post by Quzar » Thu Oct 15, 2009 2:14 pm

Well, I did it, and they seem to work fine. Only problem I had was that I stupidly forgot about the crossed wires in some ethernet cables (autosense has made it mostly irrelevant in real-world stuff), so two pins have two wires and the other two only have one a piece.

Need to figure out something to seal up the contacts (wire->rj-45 jack). Was thinking of using a hot glue gun, but can't find it around. Don't wanna spring for epoxy or anything like that. Think elmer's glue would work =P?

Edit: Turns out the internet told me elmer's would work fine, but it turned out to be conductive -_- (at least when still 'wet'). I waited some time for it to dry, but there was still bridging so I had to cut it all up. Ended up finding some rubber cement, which worked much better. All works fine now. I'll maybe post some pics later.
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Re: Keyboard extension cable

Post by Quzar » Tue Feb 09, 2010 9:01 pm

Update: (also, wow, I can't believe I've been basically without a keyboard since October o_O) turns out it worked, but extremely sporadically. I think the problems were threefold:

1) too many interface points causing a drop in signal quality over the distance (~30ft)
2) crappy headers and old cat5 cable (may have had some kinks and whatnot)
3) using a Model M, and overburdening my motherboard's USB power line which it seems is shared with the PS/2 5v. (Even if it had decided to work at some point, if I were to hit a lock key, the LED would flash and I would lose connection entirely)

So, in order to remedy 1 and 2, I finally bought a cable online. Found for a total of 15$, a 45ft PS/2 cable (only other size they had was 20 which was too short). Now though on testing it the model M still refuses to be recognized, while a crappy dell keyboard works fine.

So my thinking is: what would it take to add an external power source for my keyboard? I was thinking something like taking a short ps2 extension cable and splicing a jack for a wallwart's DC in, then putting that extension cable between the main huge one and my keyboard. Alternatively, adding a switch and power jack to the back of the model M itself.

Now the only reason I haven't cut it open and tried already is that I can't find any documentation of this having been done. Is it safe to do such a thing? Would it damage the keyboard to have power going to it without clock/data? Would I have to build a more complicated circuit than just a bypass switch so that the power from the ps/2 port would trigger the draw from the external power?

Thanks!
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Re: Keyboard extension cable

Post by Zealous zerotype » Fri Feb 12, 2010 12:30 pm

This is just my thinking. Try a battery on a crappy old ps/2 kb and old machine. I really havn't heard of anything like this, but that would be my though process.
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Re: Keyboard extension cable

Post by Quzar » Fri Feb 12, 2010 3:01 pm

Yea. The problem is that I don't have any machines build that I'd be happy with sacrificing for it, so gotta put one together. That and I'm not entirely sure how the whole process works, and using any 'ol keyboard wouldn't properly test it/it would be hard to tell if it would do long term damage.
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Re: Keyboard extension cable

Post by Quzar » Mon Feb 15, 2010 2:32 am

Well, gave it a try. Got basically no results. Took a PS/2 to AT adapter I had clipped the AT side off of, and the cable from a broken KB matched the clock and data lines and left the 5v and ground wires unconnected. Took the computer side and attached it to an LED and took the keyboard side and attached it to a receptacle that matches a 5v wall wart I have. Made sure the polarities are going the right way (... I really hope? I took - (o + to mean center pin positive, outer negative).

When connected the lock LEDs blinked (as is standard for plugging in the keyboard) but no real connection. Some keys I hit will trigger the computer's speaker to bleep but that's about it.

It seems there is a chance that the power lines are somewhat broken as when I wiggle the adapter bit the kb LEDs will blink again (as if unplugging and replugging).

Any advice?
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Re: Keyboard extension cable

Post by Ex-Cyber » Mon Feb 15, 2010 5:34 am

If the LEDs blink, the power supply polarity is almost certainly correct (LEDs, being diodes, won't ordinarily conduct in the "wrong" direction). One thing that comes to mind is the possibility that your wall wart is unregulated (which would likely cause all sorts of voltage spikes/dips during operation of the keyboard), but 5V ones are usually regulated; unregulated ones are usually 6v, 9v, or 12v.
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Re: Keyboard extension cable

Post by Quzar » Mon Feb 15, 2010 2:58 pm

The only other thing I can imagine then is that there's something about the clock and data initialization that is tied to the power on both the keyboard and PC. IE, the keyboard expects data within x ms of power on and the PC expects to be able to send it only once within x of power draw.

I guess the last test for something like that might be starting up the computer with all this the way it is and seeing if it might recognize the keyboard then (since hotplugging isn't officially supported anyways).

EDIT: Tested with a usb adapter with similar results (but no bleeping, which is expected with usb adapters). This eliminates most of my concerns about hotplugging.
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