HP262x keyboard voltage

[Rik Bos]

>
> > And using a 2392A keyboard ?
> 
>  I don't think I have one of those. What machine does it go with?

HP 2392A Terminal it has the same keyboard interface as the HP150.
Keyboards look a lot like the HP150 keyboards.

> 
> > It also uses the HP150 keyboard interface..
> > The original keyboard looks a lot like the small HP 9816 keyboard..
> > Maybe you could modify one of those.
> 
> No, the HP9816 keyboard is very different. it's a 5V 
> interface on 4 wires (+5V, ground, clock, data (from 
> keyboard)/reset (to keyboard). It also has the twiddleknob 
> (which is addressed as 1 column of keys -- 7 bits of motion 
> and 1 of direction IIRC).  Interestingly the 9816 keysiwtches 
> are not wired as a matrix, rather one side of each switch is 
> grounded, the other goes to a multiplexer input. Scheamtics 
> are on hpmuseum.net.

Yes I know and on my harddisk , very conveniant I make a lot of use of them.
And you're right I forgot the knob, just was thinking about the looks, not
the interface.

> 
> The closest keyboard i have electrically is the HP150 one.

And not realy the right style.

> It is the same interface, similar circuitry, but with differnt 
> key matrix layout. I think I can hackl that by replacing the 
> scan counter chip in the keyboard (a 4024) with a little 
> circuit of about half a dozen chips. 
> 
> The closest keyboard I have for having the right keys is the 
> one for the
> HP2623 terminal -- after all a similar keyboard was used on 
> the HP125, which as you know is a very similar machine to the 
> HP120 (to the extent that the firmware ROMs are the same, for 
> example). Of course the interface is quite differen, but a 
> conversion circuit shouldn't be too hard to buiold (probably 
> cost more for case/connectors than for logic chips!).
> 
In a lot of cases the right HP keyboards are difficult to find even HIL
keyboards are not always easy (reasonable priced) to find.
If I was you I should go for the interface and the HP2623 keyboard, it looks
better when using the HP120 ;-)

-Rik