First post & a question re:20b/30b

Hello all,

I've come here after reading about the WP34S project, and, well, fell for it. That will be my first own "WP" programmable!

I am French, so not an native speaker of English, so please excuse my clumsiness and mistakes. Do not hesitate to ask for clarifications, should you need any. Professionnally, I have worked as an EE, both in maintenance and design, (currently between jobs, alas). My main experience has been with hardware, my embedded software skills are limited to 8bit assembly, C being a really foreign language...

As for HP calculators, I've never owned one, though I have used several, starting with the HP35 then 45, 91, 21, ending with the HP41CV. I loved that one.
I've been without a "real" calculator for a long time, but this is about to change!

Which brings me to my interrogations about the 20b/30b:

1. I intended to start with a 30b (will get one later) but have found an good deal for a 20b. I think that I would not mind is "inferior" keyboard, as long as it is working well (no missed keypresses, a decent durability). What do you think?

2. I have read that their internals were identical. But looking at a photo sent by Marcus van Cube (search for "WP34S and USB"), I noticed that it did not match the PCB shown in Richard Nelson's document named "Interfacing to the HP20b V3.pdf". Specifically, Marcus' calculator seems to miss the 10pins I/O connector (J8 on the 20b schematics). I would like to have it, just in case there is a development involving these resources (interface, memory, whatever). I can't find out whether this a difference between models, or early/late versions of the same machine.
Can someone shed some light on this ?

Thanks for your assistance!



Bonsoir Etienne,

soyez bienvenu! This place is full of people with English as their second, third or whatever language, and some more where you think it can't be their mother tongue. So no need for excuses :-)

Referring to your questions, I can answer the first one immediately: Besides the (clearly inferior) keyboard feeling, the 20b is as suitable for repurposing as the 30b. Missed keystrokes can't happen, since you don't know when a key should register. For assessing durability, my 20b is not with me long enough yet.

Your question 2 needs an hardware guy to answer. That's my area no more.




Etienne, I know almost nothing of the WP 34s, but I do know English pretty well, and yours is near perfect!


Hi Etienne,

Your English is better than mine!

You are correct that they are not identical inside (compare Richard's photo of the 20b to the guts of my 30b at However, from the WP 34S F/W point-of-view, they are sufficiently the same as to not matter.

Note that the original 30b flash image does not run as a 30b when installed into a 20b chassis so there is some minor difference that HP uses to differentiate the 2. Interestingly, the 30b image in a 20b chassis seems to run virtually identically to a 20b! The 30b specific functions do not work.

(I tried the above experiment of very temporarily loading the 30b F/W into my 20b chassis for fun one day and had the wonderfully awkward experience of looking for the 30b key meanings under my 34S overlay! I had to resort to the 30b manual to figure where the keys were. For people without a 34S overlay, the experience is most definitely reversed :-) Ten minutes later, the 20b was reset to its natural state as a 34S.)


Hi Walter,

Thanks for your welcome.

I have to say that I feel very unhappy being helpless on the code side, but hopefully, I 'll find some way to contribute. I am not familiar with the ARM family, but , for my own culture and in order to help, would like to comprehend how things work at the hardware level, i.e. uC initialisation (including the possibility of Xtal detection, if that's useful) and power usage optimisation. Don't hold your breath, though...

I have ordered a 20b right away (and am awaiting cables from Gene Wright), so I should be ready to start torturing the poor beast soon.

I don't know how to express my gratitude for your -and that of your fellow musketeers- continued involvement in this amazing project.

Bye for now


Thanks for the kind words, Martin!


Hi Neil,

Great photos! Thanks a bunch, they answer some interrogations I had.
The case of the missing I/O connector is solved: on the 30b, it lies alonside the JTAG pads at the bottom of the PCB, so out of the field of view of Marcus' shot.

I also noticed that the machines seem to differ in the way the PCB is assembled with the keyboard/front plate assembly. That would be a disappointment, as I had hoped that we could have somehow married the 30b nice keyboard/PCB to the 20b faceplate (I feel black is a nice match to the overlays, and it might have allowed to get past the "black S" problem in moving towards a semi-custom WP34S faceplate).

Let's wait to see the units "in the flesh"...

And indeed, thanks a lot for your work on the assembler. Much appreciated.



Votre anglais est perfectement-superior à mon français :-)


That'ok Bill. As nobody's perfect, the rest must be pretty darn good :-)


Hi Etienne,

Thanks for the note.

This photo was taken just before I installed my 32KHz crystal. I did such an ugly job soldiering the caps in place that I did not want to post the "after" photo. :-) Is it just me and my aging eyes or do things seem to be getting smaller?

BTW: As can be seen in the photo, rather than use the often suggested jeweler's screw driver to pry the case open, I used heavy gauge guitar picks. These worked marvelously!! No scratches or dings at all!

As you noted, the pitch of the connectors is coarser in the 30b than the 20b but I think they are all present and accounted for.

It never occurred to me to swap the face plates. The black 20b might look nicer but I suspect that too many things are different on the mechanical side.

Personally I have absolutely no problem with the black overlay on the silvery 30b. In fact, I have no real problems with the overlays at all. I know many have complained about the concept of an overlay but it certainly works well as far as I am concerned.

I think you will be very much more pleased with the snappy 30b keyboard over the mushy 20b.


Hi Neil,

BTW: As can be seen in the photo, rather than use the often suggested jeweler's screw driver to pry the case open, I used heavy gauge guitar picks.

Thanks, that's precious!

Personally I have absolutely no problem with the black overlay on the silvery 30b

Neither do I, actually. But as I had seen argued in a previous thread that the 30b faceplate, as it is now, was kind of incompatible with an evolution towards a WP34S specific design (the "black S" problem), I had hoped that starting with the 20b would be easier. Well, not so, unfortunately...

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