Robot Arm Programming HP-42S??


I've started wondering if a robot arm could be used to program a HP-42S by pressing the keys. Do these arms have the motor skills to do this? Anyone here familar with the relatively cheap (say $200-250) PC controlled robot arms?

I know it wouldn't be a fast way to enter a program - but wonder how fast a robot could type. For a long program, I could envision using a text program listing, interfaced to the arm and let it do the programming over night.

What do you think -possible? - or would I just end up with a broken keyboard?


I know a person who did this using a modified pen plotter.


That's interesting - how would a pen plotter do it? I guess the raising and lowering of the pen arm could press keys. That might be a cheap way to go. I've seen old flat bed plotters at ham fests for almost no cost. And I'd think the pen arm could move up/down and relocate itself at fairly high speed - as compared to a robot arm. I just might give that a try. I'll keep my eye open at the next hamfest. I'm WD9EQD for you Hams on the list. Thanks.


I know this idea was discussed seriously in this forum a few years ago - but I would bet on serial I/O (developed by programming the extended ROM area) instead...

Best regards,

Erik Ehrling (Sweden)



Hi Erik,

>>serial I/O (developed by programming the extended ROM area) instead >>

This would be great. But.. I wouldn;t have the fun of the robot arm :)



one of the limitations was a big "what... if": what if a key fails or repeats? Not simply fail to be pressed, this is easy to check; I mean a contact failure or bouncing. It would be necessary to use some sort of visual checking, an image processor with a camera following the changes in the display to confirm a key is correctly pressed and no wrong code is added. Imagine the sequence

[STO]12 [ENTER] [X^2] [+]
being recorded by the mechanical device without back checking and the [2] in [STO]12 fails: the recorded sequence would be
[STO]01 [X^2] [+]
instead, and the program would probably fail.

I remember this fact amongst others (using an external contact array in parallel with the keyboard contacts, for instance) because I was the one asking about this particular handicap. I remember I thought about this when I bought my HP15C in the 80's, and I found that one missing key would cause many steps not to be inserted. At the end, the sequence would somehow find its own "track", but the entire program would need to be checked. By doing so, why not typing it all at once??!!

Forgive me being such a "Devil's advocate"...


Luiz (Brazil)


Hi Luiz ,

Good points on the not knowing if the keys were actually pressed. I'm assuming I'd have to check the program after entering. Could print the program to a 48GX using the IR and then upload to a PC and have a program compare it to the original. Be a fairly painless way to verify it or at least know what needs to be corrected before running it.

My other concern is the mechanism of striking the keys just the correct amount without distroying the keyboard. Another question - do all the keys on the HP-42S keyboard take exactly the same amount of key movement to register? Or would some take a slightly longer keystroke. If different keystroke lengths then might prove difficult to calibrate a single key pressure that would work for all keys.

I guess I just want to drum up a reason for getting a robot arm to play with :)


Hi, Bill;

about the IR output, you'd need another calculator OR (even better) an IR sensor (transistor) connected to the system so it would check it for you. The worst of it (I think) is the power consumption when the IR output is active. And when I considered the checking, I was thinking of a Voyager (no output of any kind...).

Have you considered a system that adapts to the pressure by... "learning"? Cursor sensing/positioning would be enough to create a database with small fuzzy and neural net SW.

The domes used in the keyboard (under each key) are essentially the same (design) and each key has the same surface area to act over their respective domes. I think that you'd not confirm such a big difference from one key to another.

The "programming" systems grows too much in size and complexity, but I guess it's no reason to give up reasoning about it. And this IS a good reason to use a robot arm; why not?

I guess yoú're not in the wrong way. The fact is that if the HP42S had a single IR input with the equivalent SW, nothing would be necessary... But I also guess that HP considered the amount of extra "customers" would go for the HP42S and probably none of them would try the new RPL models: HP28S and HP48SX/S. Well, maybe HP just wanted to give the HP41 fans the feeling that they have not been forgoten by introducing the HP42S prior to discontinue the HP41. That would be easy to take both HP41 and HP42S out of the market later, without so much "trauma".


Luiz (Brazil)

Edited: 4 May 2004, 5:30 p.m.


To be on the safe side with to long key-strokes I would simply put the calculator on a slightly elastic surface which allows the calc to move down if the pressure becomes to strong.


I don't have an answer for your question, but you reminded me of something I saw back in the '80s when I first was fooling around with microcomputers. There was an ad in one of the hobbyist magazines (I think it was Kilobaud Microcomputing) for a gadget to convert an IBM Selectric typewriter into a printer. It clamped over the keyboard and used pistons to push the keys and "type" the output from the computer. I wish I could have seen one in action!

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