Keyboard/monitor switch for Acorn A4000/A5000

[Dave Moll]

Zel's thread about connecting an A5000 keyboard to a PC spurred me into an experiment which I have been meaning to try for some time.

Thanks to another member of the forum, I am in possession of an A5000 keyboard, along with two A5000s and an A4000. What I would like to do is share a single monitor and keyboard/mouse between the three computers (and was originally going to include a PC as well - hence my interest in his query).

Given the different pinout between the PS/2 connector and that for the A5000, I now realise that I shall have to dump my fantasy of including the PC in the setup, and also that the keyboard-based switching commands of my automated KVM switch will not work. Unfortunately, experimentation shows that the keyboard signals (which include those for the mouse, which is connected via the keyboard) don't get through at all - which is disappointing but doesn't unduly surprise me. When the keyboard is connected via the switch, the A5000 displays a message "no keyboard connected" during boot up.

Really, the question that I'm working round to is whether there exists such an animal as a manual KVM switch (or even just for keyboard, as the existing switch is fine for the monitor) which would be sufficiently generalised to work with the pinout of the A5000 - or whether I will need to construct one myself. The latter should not be difficult, but I try to avoid reinventing wheels whenever possible.

[OldBoffin]

Hi Dave,
Have a look at the following - I used to deal with them when I made adapters for disabled users of Acorn machines, so know they are OK.
Stuart Tyrrell Developments: Home page
28 Apr 2009 ... Design and Manufacture of hardware for RISC OS, Special Needs and Industrial applications.
www.stdevel.co.uk/ - Cached - Similar

I still use my 2 Acorn machines on my network of 3 PCs here! Acorn is still the best for instant action - no long boot-up time!
Hope this helps,
Regards,
OldBoffin.

[Dave Moll]

I'll give them a call and see whether they can help me. I've had a look at the products section of the web page and have not spotted anything.

[Zelandeth]

A good question.

A few years back reckon it wouldn't have been a problem. Know we had some keyboard switchers back in the school IT labs which literally did just switch every line between each port - didn't care in the slightest what data or voltage was on it, was really just a bit, heavy multipole switch with one PS/2 connector on one side, and two on the other side.

Afraid I can't remember for the life of me who it was made by. Was a light brown metal case with dark brown markings and a big black plastic control knob to switch between the inputs though.

[Brian R Pateman]

These "port switchers" were available from RS among others. I might have one tucked away in a cupboard at work somewhere.

They were available with various sockets, 25 pin D and Centronics spring to mind.

This is still available (RS390-1726);

http://docs-europe.electrocomponents...6b8003390e.pdf

Regards,

[Dave Moll]

Thanks, Brian. That's just what I'm looking for.

Even if it doesn't switch the correct lines for an A5000 keyboard, I'm sure my trusty Antex can persuade it otherwise

Assuming RS still sell to riff-raff like me, I'd better order one or two.

[Brian R Pateman]

You don't need an account, register and you can buy with a credit card. If you have a problem let me know and I'll order a couple on my account.

[julie_m]

I once opened up a mechanical printer switch from a range which also included KVM switches; and it was just one big wafer switch, wired to switch all poles (including all grounds and not-useds). I see no reason to suppose the matching KVM switches wouldn't also switch all poles.

[Dave Moll]

Originally Posted by ajs_derby

I see no reason to suppose the matching KVM switches wouldn't also switch all poles.

Thank you for that encouragement. That was what I was hoping.

Brian, I'll contact you by PM.

As my quest seems to have reached a successful conclusion, I'll close the thread.