Calculator blog

Musings and comments about our common interest


Publicado el por

HP41cl, time module and battery pack

0IMG_1471Chances are you have used in your university days the HP41c family of calculators. It may have happened the same as it happened to me: I bought a replacement already in the new millennium, only to discover that it was incomplete: I wanted more and more modules, and many of them were unobtainable. More than that: it was painfully slow! Some of my programs were financial, like NPV and IRR, the latter of which iterates until it finds the rate of return that makes the NPV equal to zero. As soon as the cashflows used were more than five, it could take several unites to finish it. My HP50g was much better in that regard - but it had a much worse keyboard, and nothing of the sex appeal of its elder brother.

I then found several ways of improving its speed by “surgery”. The speed could be doubled - but I was looking for at least an order of magnitude improvement, not just doubling it!

Then I came to Systemyde’s approach. If you’re familiar with the HP41c, you will know that it was made in two types: the original one (where there were two circuits: one with the keyboard and connections to the battery, and another “pressed” against it, with the “brain” of the calculator), called “full nut” and a newer one, where all circuitry was routed in the same printed circuit, called “half nut”. Both were functionally the same, and both coexisted for a number of years, depending on the country of manufacturing.

Well: Systemyde designed a circuit that could be dropped in place of the original “brain” circuit, thanks to the fact that it was pressed, not soldered in place. This circuit would be made with the latest technology and would profit of both maximum memory and speed.

If the typical module is between 4k and 16k bytes, and current chips can easily handle 4 GB, that is, one million times bigger, why not store there all modules ever designed, and then the user could switch between it logically, i.e., plugging them in memory via a pointer instead of a physical module on the back?

So they did it. They created a number of other functions to handle that powerful brain, and gave the possibility of running at standard speed, at 50x, or several speeds in between.

Compatibility with old and new peripherals was important. They managed to ensure that all known peripherals work with it. Also all programs ever created for the HP41c are compatible too.

We at the Calculator Store have installed already a dozen of such modules, and it is a pleasure to see how well they work. The challenge is to find bodies in good shape to use them! We have to discard approximately 30% to 40% of the calculators we source - and that is reflected in the price too.

There are two HP41CL bodies with V4 circuit installed.

One is a very early tall keys machine, with satin keyboard surface, good screen and keyboard (with a slightly softer “2” than the rest - other than that, excellent) and serial number 2009A00017, which reads as “the 17th calculator made on week 9 of 2080, in the US”.

The other has what I consider the best screen I have ever seen in a HP41c-family machine. Most units start turning to a yellowish tone after a number of years. This tone slightly reduces the contrast but it is still very readable. The tall keys model above didn’t turn to yellow and still kept the grey color common to most well kept calculators. But not this one: it has a light bluish tone, which makes it the best readable, most contrasted display I have ever seen. It doesn’t even show the slight change of bright on the segments when they are off, so common in most displays

With both of these units, we offer the possibility of getting a refurbished rechargeable battery for 25 € more, or a Time Module for 120 €. Please contact us for more details at

Leer mensaje completo
Publicado el por

Available HP41CL units - and time modules!


Now we have three HP41CLs in stock.

Two of them have a v4 brain into it. They are updated with the latest circuit design from Systemyde, level v4, with the latest modules up to May.

Both of them are C models. One is a tall keys, made in 1980 and with the non-textured keyboard plate of the early machines. Excellent state. The price of this unit, which includes serial connector and cable, is 760 €.

The second is also a C model, from 1982, with normal keys but excellent keyboard and screen. It comes without serial connector or cable; The price of this unit is 625 €.

However, there is an additional opportunity: a CV model sporting a v3 circuit. This is from 2013, and therefore doesn’t have the modules that Systemyde has been programming since into HP41CL memories; however, the circuit is functionally equivalent, and you can always burn yourself the images you need with the included serial interface and cable. Another bonus - it comes with a rechargeable battery module in good shape, and for an additional 30 € you get the original Euro charger. The price of this unit is 470 €, 500 € with Euro charger included.

There is an additional discount of 25 € if you use the coupon enclosed in the newsletter that registered European users will receive.

On the other hand, there are a couple of Time modules available. There is one that comes with an English manual. The price is 150 €, although, if bought together with a HP41CL, there is an additional discount of 20 € (that can be accummulated with the coupon above)

Leer mensaje completo
Publicado el por

A curiosity on the Prime and a Time machine module

prime10Just two comments today:

First, I have realized one thing after spending 2 years with the HP Prime. You think you know a tool that you use nearly daily, but there comes a moment when you realize that you don't. This has happened today to me!

I was trying to calculate 26^6 and then I realized that the key does not say Y^X, but X^Y, just the opposite of the traditional RPN format. So I should invert the order of the operands? But wait! I have been using the calculator for already two years and I must have used this operation several times! Did I get the wrong results all the time? Because I would have never tried the operation the other way around, even if I had seen the sign on the key.

Now, when I test it, I find that it behaves as Y^X instead of what's written on the key!

Further search in the internet showed that this is a standard notation, since on algebraic notation, which is the one intended to be used primarily with the Prime, X and Y don't mean anything in particular. If anything, X is the item that comes first and Y is the one that cames last in algebraic. So this key sign has been a calsualty of the war that RPN finally lost!

And the other thing: I have found another Time Module for the HP41CL. I plan to offer a good deal to any of the purchasers of HP41CL from The Calculator Store, but for now I will put it in the website at standard web prices.

Leer mensaje completo
Publicado el por

HP41CL and time module

Leer mensaje completo: HP41CL and time module

I have found a time module for the HP41CL and I am now enjoying the facilities it provides.

The most important part, in reality, were the time functions that were already available from the beginning, thanks to the architecture devised by Monte; but it is nice to use your calculator as a machine to keep your appointments. Of course, an smartphone is much better for that purpose, even as a chronometer; but together with the HP IL interface, the HP41CL is able to control many things, like lighting, multimetres, even oscilloscopes.

You may have read my messages about the HP3468A. This is an HP-IL enabled machine. I have two units (one for me, one for the shop), that I have converted to 230v/50hz use. They work flawlessly with the HP41CL.

We have an apartment in a mountain area. We know that the voltage there is not too stable, and the drops have damaged in the past some appliances. But, of course, the local utilities company denies everything (although they have started working to improve the supply with a new transformer house nearby). To prove the point, I have set up the voltage meter of the HP3468A so that it is triggered and read by the HP41cl each 5 minutes. This way I am able to map the whole performance daily. It is a pity that this method does not allow me to see the real peaks and valleys, but at least it gives a good proxy to the real situation. Then you can make some statistical calculations, apart from knowing the waveform (since I am also storing all the points - it is a pleasure to have such a big memory). I have seen voltages as low as 193, which is 16% lower than the European standard at 230.

(By the way, do you know the reason for the 230v? I have been told that the European bureaucrats, faced with different voltages across the English channel (240 and 220v), decided to set the standard at 230 and just enlarge the tolerances. That way, the UK would continue at 240 and the rest of Europe at 220, and everyone would be happy - except the appliances, working with much wider voltage tolerances)

Leer mensaje completo