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Calculator blog

Musings and comments about our common interest


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HP Prime loading program procedure


I have been asked how to load programs in the HP Prime - apart from keying them in. in short steps:

  1. Download the HP connectivity kit (and HP Prime app, now that we're in business) from the site: HP Connectivity kit download


  • Install it in your computer. Be sure that you select the right version of your operating system. In my case it defaulted to Mac OS 10.1 - I changed it to the right MacOS version
  • Open it and connect your calculator to it. This connectivity kit also serves to update the calculator firmware, if it is not updated.


  • Go to, and navigate to the HP Prime programs that you want - there are many!


  • Choose the area and choose the program you want to download:


  • Click on "details" and on the file name:


  • Unzip the file in your computer
  • Read the .txt or the .pdf files - it is good practice!
  • Open the HP Prime. You will see applications and programs - it depends what you have downloaded
    • if the directory has the .hpappdir, drag it to the applications folder
    • hpcomm7
    • if it is a program, drag it to the programs folder:
  • And it is ready to run!! 


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HP41c repairs!


We've just received three calculators for repair: a CL that worked on assembly but not on delivery, a C and a CV. The C is easy to diagnose: corroded battery terminals. Let's see if it is the only thing needed when we open it. The CV has a beautiful battery terminal and looks solid, without any post broken - but it doesn't work!

It will be an interesting week end...

I'll try to take some pictures to illustrate further bolg issues - also with oscilloscope output views, to compare a new CL with older models, when it comes to wave frequency stability.

Please contact us at if you need your HP41c serviced!


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Back to the office!


We have returned from holidays with a new 3D design, although unrelated to calculators - a battery door for the ubiquitous Samsung TV remote!

We will have it in different colours - as a way to distinguish different remotes. It is still not created as a product, but it is on its way.

We have several products created as 3D: here is the list so far (not counting repair parts):

- Side port HP41c

- Back port HP41c

- Battery holder HP41c

- Battery holder Woodstock series (HP21, HP22, HP25, HP27 and HP29 calculators)- Shanling M0 DAP cover

- Samsung TV remote battery door (coming)

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Development priorities


We are preparing the development plans for 2020. Your requests would be listened to, but be aware that someone insisted heavily on creating the Woodstock battery bay and we didn't get an order from her finally! So we would like to have some quorum for the demands.

My list so far:

- USB connected HP41c adaptor (not battery - putting any kind of electronics inside would require huge certification effort (or alternatively huge risks for our very small company). It will be a 3D printed part with a connector. The jury is out as to whether to include a capacitor to hold the charge for longer.

- A permanently glued battery-ports connector, to hold better together with the back case.

- Many other small items for HP calculators: screws, spacers, screen plastic covers, etc.

- Finish a HP41c repair manual (we're already half way through)

Please also submit your requests to too!

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Testing HP41C with oscilloscope

When repairing a HP41 machine, it is always interesting to know what it is happening inside - regardless of the screen being blank or not. Using an old memory module, we have connected the pins with a ribbon connector, and then this connected to the oscilloscope we can see several things: is there the positive voltage? when you press a key, does it appear on the interface?

The system is designed so that when a key is pressed, there are two lines ( ø1 and ø2) that output a synchronizing wave - delayed some time the one versus the second. This is a tell-tale that the circuit is working - regardless of what happens to the screen.

Here you can see in the case of a CL just installed (thanks Mr. Lerich). The circuit is outputting 360 Khz, much more stable than the usual 343-365 that you see on normal calculators. The ringing at the corners may be due to the fact that the cables were not terminated properly and therefore there were reflections. Also it can be seen the induction effect on the rises of one curve on the other, due to the parallel 150mm of the ribbon cable.


If we see it closer, we see the rise-time of the curve is equivalent to 25 MHZ - quite a high bandwidth, even despite the mentioned termination issues. Also the stability of the voltages seem very good. Both are testimony to Monte Dalrymple's good engineering!!


We need to get deeper in this method to be able to better debug and repair our calculators. Now we need to get a service module - or an image burned into an eprom of such.


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Feet arrived!

We have received the sheets of feet for the HP41c. Tested them and work much better than expected.

We will send the 100 unit sheet for 50€ plus shipping - half the price than the 4-unit set. Ideal for collectors and repairers. 

Please contact us at


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HP Prime pro

HP_prime_front_pictureI have not used too much lately my Prime. I have been mostly focused on the HP41CL, but the other day I went to the site , which has a site with software for graphical HP calculators, dating all the way to the 48 series, 39, 40 to the Prime.

There you can see the many programs that exist now. Science, games, engineering, astronomy, you name it. 

It is interesting what you can do in games with an interpreted language like basic with modern hardware - you should try, even with the available connection kit from HP and the free PC/Mac calculator

You should  take a look at them. You can download them to your computer and from there load them on your Prime


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A HP 54201D oscilloscope

I have been using this oscilloscope from a long time, until I replaced it with the new Keysight DSOX1102G. It has taken me a long time to put in on sale for several reasons. The first is that it was missing a foot - and I don't like to sell incomplete things. So I bought a new 4 feet set and installed them. 


The other reason is that, despite its age, this oscilloscope can do things that the Keysight can't. It comes with 3 pods with each 8 signal bits + parity + groud, so that you can monitor 24-bit signals. I only indended it to use for 8 or 10 bit - enough to follow the buses of the HP41c. 


However, the sheer size and real-estate used in my admittedly small desk mandates going to the simpler, smaller solution of the keysight. But there is no denying that the oscilloscope oozes old HP quality. Even when you read the documentation, it makes reference to a long gone, quality driven time.

It has passed all the tests with flying colours and also passed the self-calibration procedures with success.

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Four new products


We have ordered production of four new products for HP41c repair - which will help many an amateur in our beloved calculators:

Lower screw - slightly longer (⅜ in) to "grab" on the lower part of the screw post (when the thread is broken with the normal size screws). Here you can see a pair compared with an original lower post screw.


Black screw: same, in A4 steel in black. Much more expensive but looks like the original.


Full set of screws!


And a spacer set to substitute the nut often found in early HP41c full-nuts. This nut can be used 2 or 3 times before it breaks the post or the thread is unuseful. The you can put a pair of spacers. As the height would depend on your zebras and your circuit, we supply 8 different heights in 0,2mm steps: from 1,2mm to 2,6mm



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The problem with ordering bulk in China

As you know, we're getting some parts produced in China. One of them is the feet for calculators we are selling. We have ordered samples from a producer, and when satisfied then we ordered a big lot. 

When we have received it, after paying the producer and 100€ in import duties, we see that the producer has "improved" the product by rounding the edges. Nice, but completely wrong for our requirements, as can be seen in the enclosed picture. The whole shipment to the dustbin! We have ordered a new production batch but will take some time to arrive.


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