PS/2 Interface (was: Wang 300 Calc]

Jules Richardson julesrichardsonuk at
Sun Sep 16 17:34:30 CDT 2007

Tony Duell wrote:
>> power on connector pins where it's possible to insert the connector 
>> "upside down".  Or using a power connector and wiring it differently 
>> than the rest of the world (e.g. MD2 diskette drives as opposed to 
>> anyone's 3.5" diskette drive).  I believe that a few old Calcomp 8" 
>> floppies actually put mains power through the signal connector on a 
>> couple of models.
> I find that very hard to believe. I would be suprised if most (if any) 
> signal connecotres met the approvale requirements for a mains connector.

You got me curious, so I just ran a search on Farnell's database for DB25 
connectors rated to 500V; it coughed up 60 different ones.

I can't think of an example where I've actually seen it done with D-types, but 
I've certainly come across it on telecomms stuff before using DIL-type card 
connectors (what I've always called 'euroconnectors', but I'm not sure what 
the official term is)

It always looks a bit worrying to be running mains type voltages over that 
sort of thing, but I expect it's well within the limits of most parts.

[wall warts]
> It also suprises me how few devices have even revers-polarity protection 
> on the input. I would have thought it would be worth including a diode in 
> each device, but anyway...

I bought one of those wall warts with a range of interchangeable connectors 
when I was in the US last. Seemed like a good idea at the time; the connectors 
were reversible so that you could swap polarity just by changing the connector 
through 180 degrees on the cable, not to mention that it came with about ten 
different sizes of connector. (the kids were getting through batteries in toys 
with lightning speed :-)

It was only when I took the packaging off that I discovered the flaw: the 
terminals at the end of the cable are marked for polarity - but there are *no* 
markings on the interchangeable connectors which give an indication of which 
of the two pins goes to the connector's ring, and which goes to the tip. 
Without any test gear it's random as to the polarity of the plugged-in connector.

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