HP-35 keyboard technology


Dear Calculator collectors,

during my researches about the HP-35 vs. SR-50 battle I noticed the clever approach of the HP-35 keyboard construction.

Tracing back the TI history of calculators you always have to start with the Datamath / SR-10 calculators. The first keyboard construction was the Klixon(TM) type with its well-known snap-action switches. It uses discrete gold discs mounted in a plastic frame on a printed circuit board and a thin and adhesive foil to protect against dust and other environmental conditions. I placed some pictures here: http://www.datamath.org/Story/Klixon.htm.

The SR-50 removed the plastic frame but still uses these snap-action discs. The famous keyboard problems started, when Texas Instruments introduced the TI-30 keyboard type with small wires and stamped, silver discs covered by black insulation foil.

Funny to know that the earlier TI-1200 keyboard with gold wires was much more reliable, but this is the art of cost reduction. Find some X-RAY pictures of the TI-30 keyboard here: http://www.datamath.org/XRAY.htm.

Hewlett Packard started with the HP-35 keyboard - a design with stamped contacts snapping against gold surface of the printed circuit board (PCB).

Today both HP and TI use Chinese keyboards but what happened between ?

I view most pictures of this HP-Museum but couldn't trace the way of HP calculators keyboards.

What I found up to know:

Second generation (HP-27) Discs against gold contacts on the PCB

Third generation (HP-31E) Experimental design followed by discs and gold contacts on the PCB (This looks really similiar to the SR-50).

Fourth generation (HP-11C) Discs against gold contacts on the PCB

Now my questions:

What was the reason to change from the simple but reliable HP-35 construction to the discs # PCB solution ?

What type of keyboard was used with the HP-41C and the later Pioneer series ?

What type of keyboard do you prefer ?

Do you "feel" the difference between a HP-35 and e.g. the HP-27 ?

What was the keyboard behavior of the HP-31E series "experimental design".

Thanks in advance for your comments.



The HP-41 used the very same golden-PCB with steel discs used on Voyager series (HP-11C and brothers), and some Spice series (later ones) used too.

Best regars!


P.S. I have scans of some Voyagers' keyboards that I fixed, and some Spices' plastic/flexible PCB keyboard also.


"P.S. I have scans of some Voyagers' keyboards"

URL, please?



I have those scans only in my PC, I haven't any web page or hosting for them...

If Dave permits I can send to him to put in some space here, I don't know if it is possible :)

They are *very large*, but I can reduce their size to send by email.

Best regards,



Send me a drirect e-mail explaining the sizes (after zipping?) and I see if I could receive them. The best place naturally is this museum.

To respond delete the obvious DROP_ and .NOSPAM



The HP35, etc keyboard used contact strips that were spot welded to the PCB... expensive to do. The keyboard disks were held down with an adhesive sheet... cheap to do.


The Ti-59 also have golden disks held down with an adhesive sheet. Is it the same technology used by HP 27,31,... ?

If yes why the ti-59 keyboard is less reliable ?

All the best

Pierre Brial


Hi Pierre,

When I used a 58 and 59 in college, they proved to be quite durable, including their keyboards. There was clear tactile feedback, no duplicate entry, etc.

I now have a TI-58C that I obtained at an antique store that works perfectly on currently available rechargeable batteries. The keyboard on this model works as well as I remember.

Needless to say, this is not exactly a representative sample, nor an attempt to refute the [perhaps valid] belief that such TI keyboards were inferior. I do agree that TI did make several inferior keyboards and calculators from a construction perspective, but in my experience the 58/58C/59 series was very solid.


I have found TI-58/59 keyboards not so reliable. After a year of admittedly intensive use 40% of my TI-59s keys were bouncing regularly, i.e. they either registered multiple times or not at all. That was when I had it repaired (just before the warranty expired) and then swapped for a HP-41CV.

Today I have two TI-59s and a TI-58C, and they all exhibit the same keyboard problem. If you don't check the display carefully, you will not know what you enter e.g. into a program.

Cheers, Victor


Pioneers use a mylar (or other flexible plastic) sheet with a somehow-formed dome under each key. Inside, at the apex of each dome, is a round spot of conductive ink. The dome provides both the snap action and the electrical contact, when collapsed against conductive traces on another mylar layer by the key above.

There are several mylar-ish plastic layers in the "keyboard sandwich" that are interposed between the calculator front (with integral, molded keys attached via flexible hinges) and a metal backing plate. The whole stack is firmly mashed together by something like 50+ heat stakes.

The conducting layer carries (IIRC) 15 traces out to exposed conductive pads. (See my not-so-clear picture of the inside of an HP-42s and notice the keyboard contacts just below the LCD.) The keyboard and LCD connections are pressed against corresponding PCB pads when the PCB is bound to the metal plate by twist-activated tab fasteners protruding through slots. (See the other picture and notice the six twist-fasteners in two rows of 3 near the top 1/3 of the HP-42s PCB.)

I happen to be experimenting with a Pioneer keyboard off & on as we post, so I'll take a picture of the various layers & pass it on for a better view of what's described above.


Hi folks,

While a "click" KB does seem to give us the perception of KB quality, I wonder how much of the perceived difference of the classic HP vs. TI keyboard overall quality is due to any difference ins firmware/ software "debounce" of the keys. Does anyone know about these routines - at least in HP land?

I have noticed that typical $20 Casio sci. calcs that have conductive rubber ("elastomer") KBs - which should be a bit 'sloppy' in terms of bounce - seem to be overall pretty good. Even my old VIC20 & Commodore 64 keyboards were nicely debounced (and you can see the 6502 ROM code that does this).

It is, given newer CPU & ROM, inexcuseable for an HP48/49 etc. calc to have any significant bounce on any key. In fact, the bounce algorithm could be made to be somewhat adaptive or user-controllable to lenghten/shorten bounce period (say, hold down two keys + the problem key at power up adjusts the key bounce timings for problem key or maybe row/column).

Really, if there's a tad of ROM space, and an available timer (or some way of knowing elapsed time - perhaps # of instructions elapsed), a few lines of firmware should vastly reduce "bounce" and should allow *very good* performance out of even a crappy keyboard. Doing this on CPUs without interrupts (i.e, polling/sampling KB) can be a bit more challenging though, and with early ROM space restrictions I can understand why a good quality KB would be needed.

A later model calc that has frequent key bounce, though, is just bad design. Even a cheap 35 cent ($0.30) 4-bit CPU w/reasonable ROM space and an interrupt and a timer should be able to support proper debounce in a few lines of code.
This should work admirably with even the WORST of keyboards.

You don't really ever see a PC keyboard bounce, do you? Differing brands may have a better or worse overall "feel", but bounce itself isn't too much of an issue [except for gross hardware failure (shorts/opens) on more fragile laptop keyboards.] These are high-volume units w/extremely thin profit margins. The firmware on its 8048-based KB controller is doing its job nicely ;)

Bill Wiese

San Jose, CA

[...who didn't have much keybounce on his TI58, none on his HP41C, quite a bit on his old APF Mark-?? sci. calc, and
and who LOVED the original 84-key IBM PC/AT keyboard and wishes he could find one again with the extra cursor pad & function keys - just the right click, and just the right QWERTY area width for his large hands.]


who LOVED the original 84-key IBM PC/AT keyboard and wishes he could find one again with the extra cursor pad & function keys - just the right click, and just the right QWERTY area width for his large hands

Have a look at this site: http://www.pckeyboard.com/index.html

Please note that I didn't buy anything from them: I was just looking for the same feeling and extra keys like you.



Thanks, Massimo... unfortunately these are still the newer style 100+ key KBs that were introduced when PS/2 PCs started coming out...

These KBs pack an extra 20 (approx) keys into a keyboard of about the same width as the original IBM PC/AT 84-key keyboard.

You might remember this old IBM AT keyboard: beside the wondrous click action, it had F1..F10 down the left side, and a numeric keypad on the right, with no intervening cursor/control key area (Ins, Del, Home, CrsrUp, CrsrDn,... etc.)

Because this KB didn't have the middle cursor area and just jumped from the QWERTY section to the numeric keypad, the QWERTY section was somewhat wider & more spacious. It was very friendly for people with large hands like myself ;) , and quite a few good DOS text editors used the Fn keys for control functions - editing was wonderful, never had to take your hands off the keyboard. (I swore by the Norton editor.)

During the transition to 100+ key keyboards, some vendors like Northgate made wider keyboards that had the new features and old features (wider QWERTY, Fn keys on both the side AND top, and the additional cursor/control keys btwn the QWERTY section & numeric keypad.

Bill Wiese

San Jose CA

Bill Wiese wrote:

who LOVED the original 84-key IBM PC/AT keyboard and wishes he could find one again with the extra cursor pad & function keys - just the right click, and just the right QWERTY area width for his large hands

Massimo Guerucci wrote:

Have a look at this site: http://www.pckeyboard.com/index.html
Please note that I didn't buy anything from them: I was just looking for the same feeling and extra keys like you.



You can still find these exceptional keyboards on E-bay from time to time. Be prepared to pay a pretty penny, though. (I have four of them - one for every computer I use. Their value makes them part of my retirement plan: they go for $50-$75 each.)

YES! The function keys at the left are the only place they should be. I can run rings around modern word processors when I use Wordperfect 5.1. As you note, your hands never leave their normal typing position when implementing an Fn operation. With WP 5.1, I can cut and paste a rectangle block before a GUI word processor user can even begin to reach for the cursor.


So THAT's why I didn't clean out the basement.... I think I still have several of these keyboards. I'll be happy to check for an extra, Bill!



Unfortunately these true IBM 84-key keyboards - at least the two I had 5+yrs ago (as well as several of their off-brand "clones" thereof) - had some problems communicating with the PCs I was using.

Problems included lock-up on boot, lock-up after autorepeat sequence, occ incorrect character, etc. Something about the communication with the motherboard apparently...

The PC motherboards were 486DX2-66s, -DX4-100s and Pentium 100s from various major quality MB mfgrs with various top-line BIOSes.

Of course, I had to use a DIN-to-MiniDIN connector adapter.

So I think these KBs aren't too useful now on modern PCs unfortuantely. If you've had better luck let me know.

My dream PC KB is still based off that 84-key layout:
- F1-F10 on left side;
- QWERTY.. layout at original 84key PC/AT width,
not narrow PS/2 width;
- cursor pad+extra keys for Windows functionality;

This KB would probably be 1.5" (?) wider than a regular current 104key clone keyboard of today.

Bill Wiese

San Jose CA


I didn't think they'd work with newer computers, but I wasn't sure. I remember that you needed the right keyboard for the computer... many of these early keyboards had a switch, "PC/AT"

I just looked, and I guess I have mostly IBM AT keyboards.



re: "So I think these KBs aren't too useful now on modern PCs unfortuantely. If you've had better luck let me know"

I've had good luck! As I noted earlier, I use only these keyboards. I am typing now connected to a home-made Soyo motherboard machine (Pentium IV, 2.4 GHz) - no problem with the keyboard. The motherboard is less than half a year old.

I know the parentage of two of these keyboards (my original and one from a friend). They came with genuine IBM PC/ATs that were purchased by our Beltway Bandit startup company somewhere around 1983. I have been using mine continuously ever since, and my friend sent me his when he upgraded years ago. I found another at the local public radio garage sale 6 or 8 years ago, and I can't remember where the fourth one came from. As nearly as I can tell, the keyboards are completely interchangeable (i.e. I've never had one work and another not work on any particular PC).

They have been used (always succesfully - never any problem at startup) with the following computers: IBM PC/AT (of course), a Gateway 486/33, the same Gateway with a speed doubler, several Gateway PentiumPro's (180 and 200 MHz, one of the 200 MHz with a speed doubler), a Gateway Pentium III 667 MHz, a Micron PIII 667 MHz, a Sony P IV (1.7 GHz, I think), a Dell PIII (at school - speed unknown), and the current Soyo 2.4 GHz P IV. Of course, on the newer machines (all except the original AT), you need the plug adapter. At the moment, I am even running through a KVM (keyboard, video, monitor) switch, with absolutely no keyboard problems.

You may want to check the BIOS on your machine and turn off the NUM lock ON-AT-BOOT option (why in the world was that ever the default?!).

I'm happy to continue this discussion here (we seem to have hit a nerve), but if anybody wants more info about my use of these keyboards, feel free to e-mail me.

By the way, the next best substitute for the original PC/AT keyboard was made by Northgate, also back in the early-to-mid '80s. It had the same "clicky" feel and sound.


Really? Was this the true-blue IBM-AT keyboard - the one with just 84 keys (ESC in upper left of QWERTY)?

Not to be confused w/original IBM PC keyboard withthe small/tall RETURN key.

When I was having these probs w/84key AT keyboards I tried some of the "Clone" keyboards that had a DIPswitch underneat for "AT vs PC" selection - neither setting fixed the problem.

Also, these problems occurred in DOS as well as Windows (3.1).

Unfortunately the time has passed for these keyboards' layout. While I *LOVE* their large QWERTY layout the lack of some other keys and not having a separate cursor pad is a little difficult nowadays.

If someone would just make a keyboard with a *LARGE* QWERTY... area and put some PF keys down the left side, I'd be VERY happy

Bill Wiese

San Jose CA



Mine are all "true-blue" IBM PC/AT keyboards (i.e. they are what IBM shipped with the AT computer, circa 1983 or 1984), however the ESC key is at the upper left of (above) the number pad on the right-hand side.

Take a look at the keyboard in this url: http://www2s.biglobe.ne.jp/~yav/comp/pc/keyboard/ibm84e.html

The owner of this one seems as ecstatic about his as I am about mine. The total width of the keyboard is about 18 inches.

What kind of problem(s) did you have? Did the PC just not recognize the keyboard?


I have a "classic" (IBM 42H1292) 101-key buckling spring keyboard from PC Keyboards. It works fine on current model computers.


Sorry Bill, I misunderstood your message and overlooked the "84" keys statement...

However I was quite certain that at PCKeyborad.com were selling 84-style keyboards too: I surfed their site (looks like they are redesigning it) but found no reference to them, only specialized layouts such Emulator or Point of Sale. These have both the left keypad and function keys on top.
They also offer a customizing service... who knows?

And yes, I used and remember well the XT, AT and advanced keyboard layouts. I eventually got used to the latest one and still prefer it over the others. But what really made those kb apart was their tactile feedback, of course: gimme back that click! I hate mushy keyboards (my wife - sleeping next door - may be of a different opinion...).




Yes, I have grown somewhat tolerant of the new layout.

I use the PFE32 programmer's editor - and if I could set up some macros on PFkeys down the side of the KB it's be marvellous.

The click is indeed nice. But for my larger hands, having the larger QWERTY.. area (maybe 10%) really speeds things up...

Bill Wiese

San Jose CA

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