2 Jul
2013
2 Jul
'13
7:19 p.m.
Just picked one of these up, sans keyboard. This may be the only HP
computer I'd dare to call "cute." I thought I had a keyboard that would
be compatible with it, but it turns out I do not -- anyone have one
going spare?
Thanks,
Josh
3 Jul
3 Jul
11:14 a.m.
Just picked one of these up, sans keyboard. This may be the only HP
computer I'd dare to call "cute." I thought I had a keyboard that would
It's a lovelly little machine... I assume you;ve taken it apart. You can
remove everyting apart from the PSU by releasign 2 thumbscrews (the
expsinon slot cover or expansion board), 2 quater-turn fastners (top
cover) and one screw.
I don;t know how much RAM you have, most had 2 rows of 4164 chips for a
total kof 256K. There';s quite an easy mod to get 1 Mbyte on the
mainboard, basically it's fit 41256s in place of the 4164s, add a
74S158/7rF158 in the spare location on the mainboard, I think add a 33R
(or is it 22R) resistor amd cut some jumpers. I did it to mine.
be compatible with it, but it turns out I do not --
anyone have one
going spare?
Argh AFAIK that keyboard is uniqueto the 98716. Mo other HP uses the same
keyboard. Actually, is the older version of the 9920 keybaord the same???
The HP120 and HP150 keyboard look to have a simialr interface, but they
don't. If froget which way roudn it is, but in one case the keyboard
outputs a signal to say it's starting a scan (that is, the next key sent
will be logical key 0) and the other takes a signal from the main machien
to reset the scan counter. So beacially, the 'start of scan'signal goes
in oposite directions in the 2 cases.
Anyeway, the keyboard itself contains nothing custom (it's all 4000 CMOS)
and scheamtics exist. WHich means you can dedcue the interface details.
It would be too hard to make soemthign that will work if you can't find
the originak
Basically, the keyboard sends the state of each key one after the other.
Note that some positions are used for the count (7 or 8 bits, I forget)
and direction (one bit) of the tiddleknob. Yes, the coutner for that is
in the keyboard.
The original keyboard has one odd design feature. It's not an electrical
matrix of switches. One eide of each switch is gorunded, the other goes
to an input o na 4051 multipleser. It's the only keyboard I've ever seen
like that. Where it was done to reduce RFI I do not know.
-tony
5 Jul
5 Jul
9:29 p.m.
On 7/3/2013 11:14 AM, Tony Duell wrote:
Yes, it's very easy to get open. A very nice design. This one's in
good shape (aside from residue from many, many asset tags) but the
screen has a fair amount of burn-in.
Cool, thanks for the info. Good to know it shouldn't be too difficult
to build a replacement; I hope I can find an original to match, though.
Not in any hurry, I have enough other projects to keep me busy until one
turns up...
Thanks again,
- Josh
Just picked
one of these up, sans keyboard. This may be the only HP
computer I'd dare to call "cute." I thought I had a keyboard that would
It's a lovelly little machine... I assume you;ve taken it apart. You can
remove everyting apart from the PSU by releasign 2 thumbscrews (the
expsinon slot cover or expansion board), 2 quater-turn fastners (top
cover) and one screw.
I don;t know how much RAM you have, most had 2 rows of 4164 chips for a
total kof 256K. There';s quite an easy mod to get 1 Mbyte on the
mainboard, basically it's fit 41256s in place of the 4164s, add a
74S158/7rF158 in the spare location on the mainboard, I think add a 33R
(or is it 22R) resistor amd cut some jumpers. I did it to mine.
Looks like I have 1.25MB of memory in this thing. (256K on the
mainboard, plus a 1MB 98257 in one of the expansion slots.) It also has
the graphics option fitted. Guess I could get 2mb if I modified the
motherboard, but we'll see...
be compatible with it, but it turns out I do not
-- anyone have one
going spare?
Argh AFAIK that keyboard is uniqueto the 98716. Mo other HP uses the
same
keyboard. Actually, is the older version of the 9920 keybaord the same???
The HP120 and HP150 keyboard look to have a simialr interface, but they
don't. If froget which way roudn it is, but in one case the keyboard
outputs a signal to say it's starting a scan (that is, the next key sent
will be logical key 0) and the other takes a signal from the main machien
to reset the scan counter. So beacially, the 'start of scan'signal goes
in oposite directions in the 2 cases.
Anyeway, the keyboard itself contains nothing custom (it's all 4000 CMOS)
and scheamtics exist. WHich means you can dedcue the interface details.
It would be too hard to make soemthign that will work if you can't find
the originak
Basically, the keyboard sends the state of each key one after the other.
Note that some positions are used for the count (7 or 8 bits, I forget)
and direction (one bit) of the tiddleknob. Yes, the coutner for that is
in the keyboard.
The original keyboard has one odd design feature. It's not an electrical
matrix of switches. One eide of each switch is gorunded, the other goes
to an input o na 4051 multipleser. It's the only keyboard I've ever seen
like that. Where it was done to reduce RFI I do not know.
-tony
6 Jul
6 Jul
11:23 a.m.
I don;t know
how much RAM you have, most had 2 rows of 4164 chips for a
total kof 256K. There';s quite an easy mod to get 1 Mbyte on the
mainboard, basically it's fit 41256s in place of the 4164s, add a
74S158/7rF158 in the spare location on the mainboard, I think add a 33R
(or is it 22R) resistor amd cut some jumpers. I did it to mine.
Looks like I have 1.25MB of memory in this thing. (256K on the
mainboard, plus a 1MB 98257 in one of the expansion slots.) It also has
the graphics option fitted. Guess I could get 2mb if I modified the
motherboard, but we'll see... Cool, thanks for the info. Good to know it
shouldn't be too difficult
to build a replacement; I hope I can find an original to match, though.
Not in any hurry, I have enough other projects to keep me busy until one
turns up...
I got one minor detail wrong (but it's obvious from the scheamtics).
There are really 2 signal lines between the machine and the kayboard.
One, from machine to keyboard, is a clock line.The other is
bidirectional. From keyboard to machine, it indicates whether the key is
pressed (or the appropriate bit of the twiddleknob counter). But if the
machine asserts in on the appropriate edge of the clock (it's clear from
the schematics, which are not in front of me), the scan counter in the
keyboard is cleared. That's the 'reset'
If you ahv to make one, you have a choice. You could copy the original
design, it's just common 4000-series CMOS parts, nothing custom or
programmed. Or I'll bet a microcontroller could easily keep up with the
interface singals. so you could use that.
-tony
4187
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4190
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