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Calculator blog

Musings and comments about our common interest


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Compiling program sets for HP15c

Captura_de_pantalla_2024-05-07_a_las_19.52.46As it would be good to share programs for the HP15c, we have Torsten's fantastic HP15c simulator that allows to write and document programs for the HP15c.

So far it can also be used to interface with Swiss Micros' DM15 calculator, but it would be possible as well to interface with the HP15c CE, since it has a USB connection, albeit with an odd connector. The format of the HP15c CE file will be different.

This opens the possibility to create application pacs for the HP15c, with sets of programs. The simulator allows for proper documentation of the programs, and you do not need to choose anymore - you have close to 1000 program lines. Your limitation is the number of labels - just 25! (Believe me: this is a limitation when putting together many programs)

I have been considering which pacs should be created. One will be the Financial pac: I have already many programs (most of the original HP41 Financial pac), but there is room for more. I am considering including Black and Scholes, although that one belongs to the Securities pac. I am also looking for a good solution for amortization schedules, making use of the TVM existing routines.

Math Pac is more complicated: we need to think from scratch because the HP15c has already many of the features of the original pac: matrix and complex numbers!!

We'll continue with more pacs when we have finished with them - but please also reply if you want a particular set of programs be put in a particular pac.


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Testing new repair method for HP41c lower posts

I am now testing a new method to repair the lower posts. Do not worry - it does not change substantially over previous methods - it is just a simplification.

I hate gluing. I have always hated it. I always made a mess of it when I was a child and I was assembling aircraft models. A disaster. And I have improved with my skill, but just a little, and I still hate it.

The piece we designed for the lower posts had a grip on the lower part:

Captura_de_pantalla_2024-05-21_a_las_10.05.52This grip has the thickness of the calculator keyboard circuit. If we drill the holes with a little circular motion so that there is a small room below the circuit for the grip to hold, and if we use our long lower screws (this does not work with original screws), and we press down when we screw the calculator together, then we mya not need to glue the piece down!! The piece was designed with a small inward angle - and the grip gets expanded when you introduce a long screw, pressing sideways and securing the part.

When gluing the piece down, you need to be extra careful to cover all small keyboard holes. If these are covered by glue, that key may not work and you can only disassemble the whole keyboard. If we do approve this method, the whole gluing process is not needed and there are some pieces (the keyboard support and the clamps) that are not needed anymore!!!

I also would have to slightly modify the upper post repair part to give it a stronger grip too. Let's see if this works.

You can test with your HP41 during repair - it is a non-destructive testing and you can always glue it if not satisfied!!

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A request for HP15c heavy users

Now that we can reasonable expect to have the possibility of saving and restoring HP15c memory in the near future, and even interfacing it with external software, we could envisage to have software pacs for the HP15c - just like we did for the HP41c. We have 25 labels and that can account for many programs for a given subjext - even if some labels are used for the programs inner subroutines.

What would be the software pacs you could like to see first? What would be its composition? I can imagine some (I will be updating this post as ideas come to me):

  • Finance
    • TVM
    • NPV - IRR
    • VAT-less value
    • %T
    • Date difference
    • Black&Scholes
  • Electrical Engineering
  • Mechanical Engineering
  • Surveying
  • Navigation
  • Aviation
  • Astronomy (with many astronomical objects)
  • Structures
  • Matrix Algebra (including the superb work of Valentín Albillo)
  • Physics
    • Important formulæ
    • Physical constants put in registers
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Some clarifications about the HP15c CE

I have seen in Facebook several opinions about the HP15c CE and I would like to comment on them.

  • The HP15c CE and HP15c LE are not "the same calculator": there is a different processor, more advanced and with less consumption. Also the keyboard quality is superior. Battery life is at least 6 times better on the CE than the LE. My first CE is still running with the first set of batteries despite being my main calculator. 
  • The HP15c CE is reallistically firmware upgradeable. By "reallistically" I mean that there is a method and a non-DIY cable available here. Also, the HP15c CE is very difficult to brick: I have modified with new firmware more than 200 units with no failure whatsoever. 
  • All the known bugs of the HP15c LE have been fixed in the first CE firmware.
  • The CE comes with more memory: 98 registers instead of 65 - and there is a hidden method to get to 194. This opens up a lot of application possiblities, regarding long programs and/or heavy matrices (you can have, for example, 3 8x8 matrices simultaneously!).
  • The CE comes also with a hidden, non-supported HP16c "clone" inside. To make use of this clone there is an available silicone overlay with the HP16c key set up. The original firmware has a bug, but this is easily solvable with the programming cable. Below a calculator running the HP16c clone without the bug.
  • IMG_0958
  • The USB connection (albeit with a non-standard plug, solved by the cable) can allow backing up and restoring memory (increasingly important with the extended registers) and interfacing with external software HP15c simulators, with just a firmware change. This also opens the possibility of software pacs (Finance, EE, Mechanical engineering, Algebra, etc.)
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A small teaser....

Hopefully not too far in the future...


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Interfacing with your HP15c CE

As you know, your HP15c CE has a USB connection in a 6-POGO pin connector in the batterty bay. This connection can be used with a cable, and so far has served to fix the firmware of the machine to fix several bugs.

Now we are testing its use to back up and restore the calculator memory , and also to interface with external software, to modify programs and document them. It will be fantastic to be able to do so - which was not a possibility when you bought the calculator!! Also: no more costs involved, aside from the interfacing cable.


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The innards of the new HP15c CE


I tried to work on the keyboard of a HP15c CE. I opened it, taking out the 5 screws (do not forget the one beside the battery!). Here is what can be seen inside:


If you are DIY inclined, you could add a standard nano-USB on the left side of the calculator (which is on the right side in the picture). Beware: it requires drilling your precious unit!

On the other hand, no way to go into the keyboard: many permanente fixings, risking to break the calculator.

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Continuation of "New glue..."

I have been using the Schwanheimer Industriekleber 100 glue already for some time. When properly using (making generous use of the primer on both sides) it is the best glue I have used for calculator repair. Better and thinner than E6000; no comparison with E6000+; and miles ahead than other cyanoacrylates. I think the primer makes all the difference.

You can read my initial feelings on this glue here:

So much so that when the glue is finished (the primer is not, yet), I have gone to their website and bought the whole pack: it comes in a portable plastic bag. I am looking forward to finish all the repairs that I have in front of me, and I will report later. It includes an accelerator, a filler, a mechanizable patty and a solvent too. 



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Next developments for the HP15c CE

The enhancements I foresee for the HP15c have to do with the cable and firmware posibilities:

- Backup and restore user memory

- Some kind of memory manipulation of the user memory file, so that it can be used in other software like Thorsten Manz's fantastic HP15c. 

Both things together can create an ecosystem for the HP15c. So far, entering a program was cumbersone and had to be done each time. With backup and resotre, + memory editing outside of the calculator, you will be able to exchange software between users - and development and use will skyrocket compared with having to enter any single program yourself. 

Let's see. I have heard that there are already firmware prototypes to do that.


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