Calculator blog

Musings and comments about our common interest


Published on by

HP15c Manuals


We have included a HP15c Manuals page, where we link to HP15c manuals. There are several languages - including even Japanese!

You can find the page HERE


Read entire post
More about: Manuales, hp15c
Published on by

HP10bII+ and newest HP12c "on its way"

We have been told by Moravia that the HP10bII+ and the HP12c (of the newest version) are now on their way in a boat from the Philippines.

Compared with the previous HP12c, the newest has the same innards (as shown in the previous blog release), but the bezel looks much more "metal" than the plasticky bezel of the last version. They clearly look better.

The HP12c is many times faster than the HP12c platinum, due to its atmel processor. It is also several times more efficient in consumption than the original HP12c+ and Anniversary - the processors are different and much more evolved when it comes to energy consumption. When I have some time, I will make a comparison.

Due to the programming model, much simpler than the HP15c, it is also significantly faster in simple programs than the Atmel-based HP15c. Go figure! Now, the HP15c has a much wider range of functions, and also much more memory for registers and programs.

Read entire post
Published on by

A HP12c's innards

Out of curiosity, I wnted to open one of the latest units of HP12c that I have received. This is a normal unit, made during HP's tenure in the Philippines (I think the actual producer is Kinpo, but I am not sure). Let's see what we find within!

When opening it, you have to remove the 4 feet in the corner. There are 6 screws to unscrew (do you find the sixth?). Trying to open it without unscrewing all will destroy the case.


The sixth screw is below the right battery. Careful!

Once opened, both sides are united by a three cables that carry the power from the batteries. The circuit, on the other hand, is visible in the back of the keyboard. It is very concentrated around the main processor. There are a couple of copper pads that I don't know what they are for. There are also a couple of small springs that are exceedingly easy to lose (This is common to other Voyager calculators of all vintages)



The white band below is an adhesive. again, I don't know what it is for. I have removed it and found nothing to protect below it.

The 6-point connector is a POGO 6-pin connector, but it is connected as a USB interface, as well as a reset device, by shorting specific pins. The problem is that this connector is completely non-standard. There was one produced long ago for the HP15c Limited Edition, but it has a completely different connection schematic. If you have one from that time you can modify it - but it won't work as is with the new calculators.

Is there not another alternative? Yes, it is. In the circuit there are provisions to solder a true USB nano connector. Where? in the right side of the circuit. Here:


I don't know the exact part number that can be connected here. You'd need also to break the case, or have opened each time you want to change the firmware. If you look into, you'll find that there is people around still interested on Voyager firmware mods. You could eventually want to repurpose the calculator for whatever type of calculator or functions. You have, though, the wrong keyboard for it. You would need to consider creating a silicone film with the lettering of whatever you want. 


Read entire post
Published on by

HP10c for repair!


The other day I had the opportunity to repair an HP10c calculator. I had not seen such model before! Yes, HP11c and HP15c are better, but the HP10c is the rarest of them all. It was a well used, worn unit, that did not work. I think that the problem had to do with dirt and corrosion, because once cleaned internally with anti-rust fluids it worked just after assembly.

I was able to make it work, though:


When opening it, it was of a more advanced design that I am used to, with a fully covered back that showed a large circuit, instead of the several smallr found in HP15c or old HP12. It also had a flexible circuit I was not used to.:



Read entire post
More about: HP10c, hp15c
Published on by

Happy new 2023

Dear Calculator-lovers,

We wish you a very happy 2023. Hopefully, this year will come with some nice news regarding our hobby - and maybe even new HP-branded calculators! Stay tuned since you will see it here first.

Apart from whatever comes from the HP brand, you will get here at least three new HP calculator related products - specifically produced by us.

Have a nice year and take care.

Read entire post
Published on by

Valentín Albillo's Articles


Valentín Albillo is a Spanish pioneer in HP calculators. He has been writing articles about several HP calculators and computers for a long time. He has a soft spot for the HP71b, but he has written articles for most of the HP vintage models.

I had a page linking to his articles in his previous website, but now that that one is down, has hosted Valentín's articles in their website. I just had to update the links to the new site!

You can find here the page that links to all of Valentín's articles:

Valentín Albillo's articles

And here you have one of them, describing, praising and using my preferred calculator: the HP15c:

HP Article VA006 - Long Live the HP-15C.pdf


Read entire post
Published on by

Even more memory in a HP15c LE?

For those of you that have a HP15c LE, and remembering the previous post about cabling to repurpose a 12c to a 15c - now there is something that can be interesting to you!

The forum thread is here:

At the beginning of the post (already cited in the previous blog installment), they discuss the different HP15c firmware available, and they post three of them.

But later in the thread, there is a discussion on how to increase calculator memory in firmware, by patching the original ROM that is in every HP15c. The ROM adressed the available memory of the original calculator, but in the emulated system there is more memory! So there have been several attempts at increasing the memory by patching the original ROM in selected places.Someone has reached 128 registers (the original machine has 64), and there is an in-depth discussion on how to reach 192 registers. J-F Garnier even posts the ROM positions that need to be patched. 

With that information, we have been able to create a patched ROM that allows for 192 registers. The firmware by default offers 94 registers and 99 non-allocated registers for programs and matrices. With this split, you could use 693 program steps. This is a screenshot of the MEM command, showing the above memory scheme. However, other splits are possible.




Read entire post
More about: hp15c
Published on by

Reprogramming a HP12c into an HP15c

There is still a lot of demand worldwide for the HP15c calculator. While the HP42 was arguably a better calculator, the sheer elegance of the HP15c beats it every time. All keys had three functions - at least, since some key labels could be understood differently if you were working with numbers or matrices (yCx and yPx), or as matrices or program labels (A to E keys). 

Si ti is no surprise that people want to get hold of an HP15c "on the cheap". the easiest way is to reprogram a current ARM-based HP12c. There was a recent discussion in on hp15c firmware for the old Hp15c LE edition issued in 2011 - and it was posted there ( I will not do it here due to copyright issues - at the end this is a business and it is better to stay safe)

To do it you need a cable to connect your computer with a JTAG connector like the one in the back of the calculator. these connectors are made of POGO pins, and are increasinglt rare:


It is the 6-pin connector in the middle. This is a recent HP12c calculator. Beware with the cable: there are two types of HP12c ARM-based. The ones prior to 2015 were based on an Atmel AT91SAM7L128 and the communication protocol is serial RS232; while after that there was a new model based on another chipset, the Atmel AT91SAM4LC2CA, and here the connection is USB !! (with the same outward connection)

I enclose here a screenshot of discussion about the pinout of the two calculators:
















You can get there more information on how to get the cable. Good luck!

Read entire post
More about: HP12c, hp15c
Published on by

Register arithmetic on the HP15c

There had been register arithmetic features in other HP calculators before, but never with the depth and variety of the HP15c. We’ll see it in a moment.

What do we mean for register arithmetic? Let’s see how you would work with the contents of a register. Say that you want go get the contents of a register and add them to the X register. Without register arithmetic, you would need to call the contents of the register to X (RCL 5, for example), and then press “+” (by doing this, you would have raised the old X to Y, the old Y to Z, the old Z to T, and the old T would be lost – something to take care about when programming)

With register arithmetic, you would just do RCL + 5, and while the number of keys is the same, you don’t loss the T register! 

I may agree that RCL + (or -, x or /) are interesting but nothing to write home about. However, you can do the same with STO: add the X contents to a register. This really saves strokes, and it is much more elegant: compare:




with register arithmetic:

STO + 5

It also makes for shorter programs. Be careful with the division and subtraction operations: you need to remember that the second operand is always the one in the X register.

There are other interesting operations, involving the I register: you can operate with the contents of the I register, (STO + I), or with the contents of the register adressed by the content of I: STO + (I). These are very useful when programming – really clarifying the program flow

(Not related to register arithmetic, but worthy to discuss here too, is the exchange of X with the contents of a register: either a direct number (0 to 9, .0 to .9), the I register, or the register indicated by the contents of register (I): you use the key X »«)

Read entire post
Published on by

HP15c book

image0As the HP41 repair book has already passed the 500 units sold mark, I have been challenged to write a book on the HP15c.

Many years ago, there was a book called "An Easy Course in Programming the Hp-11C and Hp-15C (Easy Course Series)", by Ted Wadman and Chris Coffin, which I have not been able to get hold of. Then you have the fantastic user manual and also the Advanced functions manual - in itself a computer science crash course. Then there are many sites that have several programs, but nothing like a common respository with all known applications.

I am not the only one to love the HP15c. Its compact form factor, the ability to use it with both hands for a faster keying in, the complete and consistent fucntion set, the good memory sze for its time, made it a formidable calculator for the engineer and scientist calculation, when he was far from a computer. I still use it every day and the search statistrics of my site still show it as the most searched item - after all these years.

The manual will describe the machine, list its several versions, explain how its firmware can be upgraded, and will list many programs for all areas of scientific knowledge and for all educational levels. Most of the information is already available if you know how to search for it, but I have missed a place where you can read all of it with a consistent writing and enough explanations on what each program is doing.

You may say that it does not make sense to write a book about a discontinued calculator, but I know for a fact that there are many of them still in use around the world, with peaople searching for software and longing to read more about it.

Besides, I do not lose the hope of having it produced again...

Read entire post