HP262x keyboard voltage

[Rik Bos]

I'll look around for you and will place a small posting on our Dutch
collectorslist (cvml).
May be something comes up (not a great chance).

-Rik

> -----Oorspronkelijk bericht-----
> Van: cctalk-bounces at classiccmp.org 
> [mailto:cctalk-bounces at classiccmp.org] Namens Tony Duell
> Verzonden: zaterdag 4 april 2009 22:01
> Aan: cctalk at classiccmp.org
> Onderwerp: Re: HP262x keyboard voltage
> 
> > 
> >  
> > 
> > >
> > > > 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.
> 
> Hmmm.. I don't think I have one, but _somewhere_ I have an 
> obscrue HP keyboard with a 6 wire RJ11 connector. Maybe I 
> shoukd try to dig it out.
> 
> 
> > 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.
> 
> As you know by now, the frist requriement is that the system 
> works. The 
> correct 'looks' are very much secondary to that, particularly 
> in a case 
> like this where I am not going to modify the HP120 in any 
> way. If by some 
> great chance I get the correct keyboard I can just plug it in.
> 
> > 
> > > 
> > > The closest keyboard i have electrically is the HP150 one.
> > 
> > And not realy the right style.
> 
> Ture. 
> 
> > 
> > > 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.
> 
> Now those I am not short of (both the HP46020 (individual 
> swtiches) and 
> HP46021 (capacitve membrane assembly). 
> 
> > If I was you I should go for the interface and the HP2623 
> keyboard, it looks
> > better when using the HP120 ;-)
> 
> I'll probably do both in the end. I spent the afternoon pulling HP 
> keyboards apart and buzzing out connections/ The HP2623 
> keyboard is much 
> as I expected, and the switch matrix layout looks to be right for the 
> HP120. Which means iternfacing it is just a matter of adding a 7 bit 
> counter (4024 or similar) and maybe an inverter to step 
> through the keys. 
> Actually, I'll probably add some buffers too, I don't like 
> driving cables 
> from the output of flip-flop chips...
> 
> The HP150 keybaord is also as I suspected. Modifying that one 
> should be a 
> matter of removing the 4024 scan counter chip and replacing 
> it with a PCB 
> contianing a 7 bit counter an an EPROM. What makes it a 
> little more work 
> is that this keyboarsd runs at 12V, all EPROMs ruin at 5V or 
> thereabouts. 
> So I'll need to add level shifters. But that's not hard.
> 
> -tomy
> 
>