Unabashed HP 41CL promotion (with pictures)!


What a facinating project Monte has undertaken. The board is working flawlessly for me.

Currently it is configured with my resident programs for work complete with key assignments.

Also I have physically inserted the following:

- port 1 serial connector which leaves port 1
- port 2 Diego Diaz's Clonix
- port 3 time module
- port 4 reserved for IR printer, HPIL, laser wand, card reader.

Virtually installed are the following:

- port one lower the HP41CL suite of commands including plug and
uplug, turbo and etc
- port two Clonix with CCD, PPC, NAVB1 (all removable and
interchangeable with the pic programmer and Diego's instructions.
- port three with MATH and ADVANTAGE roms
- port four with STAT and TREK roms

The turbo mode* runs my WPA (way point data) routine in 7 seconds including prompted key inputs giving Great Circle and true track. This is fast as the program relies on a data base of airport codes attached to Lat and Lon co-ordinates. So not only calculating the GC distance and track but scanning the extended memory for the prompted for airport three letter code (Vancouver YVR) and converting lat and lon alpha into numeric.

Contrast with 30 seconds without turbo50 mode!

Well enough said, with the addition of a couple of small programs in memory to assist in plugging and unplugging the roms this is one of the most incredible scientific calculators today.

The calculator I chose is a tall keys (actually steeper front) with an early serial number (yep, Gene, not as early as Richards!) but still. It had a defunct board which I have yet to trouble shoot. The case and keys were perfect. No cracked screw posts or shell. All keys with an incredible HP snap. Crisp clear LCD panel. The presence of power supply contact balls.

So the completed project, with a capacitor modification due to the LCD driver revision.

The pristine OLD NEW **HP 41CL**

The early serial number 1933A...

The port configuration with the serial connector beside clonix:

The external contact balls/springs/clip (see The CL conversion of an early HP 41C )

*There is a note in Monte's manual that the turbo mode does affect power drain and shortens battery life. That is another reason I selected this calculator as it has the power supply ball contacts. With a modified TV cord which I will put together soon I can attach this to an external power supply if required. This is mentioned in the annals of history 'HPNotes'. So having the external power supply ball contacts makes life easier if you are in an office. In fact, wiring the cord to a large lantern alkaline 6 volt battery would suffice.

Also, you will need a time module for the calculator as the 41CL board does not have a quartz crystal. Of course this is required on the C and CV version but also on a converted CX to CL as the CL board contains the timing functions but not the running clock.

Enjoy and if you are an HP 41C, CV, CX you must have one of these CL's. This is now back in the cockpit as it is as fast as the 42S in turbo50 mode!


Edited: 15 June 2011, 6:38 p.m.


It would be great if some of you could whip up a wiki on wikia.org to capture all this knowledge truly.


It would be great if someone would use my wiki (www.wiki4hp.com) to put it there! ;-) The more we can share this kind of information, the better. I totally agree!




There you go :)


Hello Bruce,

I will clean up the previous post and add it to this one. Then post at your wiki site.

This is also included in the HP 41C chapter of the book.

Cheers, Geoff


I think I know what you next vocation will be after you are doing with flying airplanes!




Selling Realestate in Florida at low tide? Something like, "I have 40 acres for you at low tide," ;-)

So much to do and so little time!

Of course the force us to retire at 60 although there are a few human rights complaints on that one. So what to do at 60 (a few years away ;-)


Edited: 16 June 2011, 1:47 p.m.



that's one cool calculator!

what's that input jact above the time module?

hpnut in Malaysia


RS-232 port


HP 41CL site


HPnut, I didn't know a thing about the 41CL board until HCC2010 and Genes presentation on behalf of Monte.

HP 41CL HCC2010 link

This is ALL Monte Dalrymples baby. Go to the site Gene lists and look at the above video. All I did was install it in the shell of a 41C per Montes instructions.

By the way there are now 9 ROM images installed in that puppy. With 450 of the 600 extended memory registers loaded with data and programs while a full list of programs are residing in program memory.

I will be using this overlay on the calculator as it has replaced my 41CX. I needed the realtime function for my program so the time module is required.

I wonder, can the time module be hardwired into an area inside the calc HHHMMMMMM!


Edited: 16 June 2011, 11:29 p.m.



I wonder, can the time module be hardwired into an area inside the calc HHHMMMMMM!


I'd be looking REAL hard at the port that the RS-232 shell covers. Some thoughts:

- Hardwire the internals of the TM to the port occupied by the RS-232 shell and mount the TM board inside the calculator?

- Move the RS-232 connector to another edge of the calculator, perhaps using a more compact connector (e.g. mini USB, ribbon ZIF, etc)? A stroll through Akihabara next time you're there might be spark some ideas.

- Bluetooth<->serial module mounted internally. (Perhaps Monte might add this to the NEWT board?)



Blue tooth

nice touch!!!!



Blue tooth
The problem with Bluetooth is that it is defifintely not hacker/hobbyist/workbench friendly. I've tried with a couple of companies who offered development kits where everything is supposedly done for you, yet I ended up giving up, telling my employer I wasn't going to try any longer, at the risk of losing my job. (I didn't lose it.) Then I found out that he gave me the job because another engineer had tried and told him the same thing, and he didn't believe him, and didn't want to tell me. The data sheet for the module was a couple hundred pages, and after getting through it, you have more questions than answers, and no idea of how to get to certain requirements. RS-232 is extremely easy by comparison.

I looked into the Bluetooth option. There should be room inside the calculator body (but not on the 41CL board itself). But after spending a day going through the specs, I realized that it was going to take a LOT more time to write the necessary software than I wanted to invest. Call me a Luddite, but RS-232 works and doesn't take a lot of power. For me personally, I will very rarely actually be uploading or dowloading anything, so RS-232 is sufficient. But other users might be different.


I was actually thinking of using one of the dedicated RS-232<>Bluetooth modules, vs. a more generic BT chip dev kit and all the associated headaches that come with that. These generally have a dedicated microcontroller (or core) running the BT chip and your application talks to that.

The ones Sparkfun sells accept simple "AT" commands on the serial port to set up the link, etc.

Drawbacks are these modules are pretty spendy (40-60 USD) and are a bit bulky. Upside is they are available with TTL serial interfaces and work from 6v.

Completely agree with the wired approach if that answers the mail for a given application. No extra power required and one less thing to go wrong.

But it's fun to think about!


Edited: 17 June 2011, 11:15 p.m.


Hey Geoff:

Dumb question. With all your 41Cs, how do you tell the 41CL from the rest?

I'm looking forward to HHC2011 this year. See you there.



Dumb Answer:

click here

or look at this:

but seriously; two 41C's (79 and 80), two CV's and five CX's.

The CL is now the main calc but an identical CX (slower and with only the Diego Clonix) is the backup!

Cheers, Geoff

San Diego should be a GEEK FEST of a meeting, WP-34S, HP 41CL and etc.

See YOU there!


Edited: 17 June 2011, 6:49 p.m.


Hard-wiring modules wasn't uncommon in the '80s during the '41s heyday. They'd be stripped of their enclosures and contacts then the bare circuit boards mounted vertically between the ports and the side case of the '41 where two per side could be squeezed in. Wire-wrap wire (i.e. 30AWG / 0.25mm) was connected point-to-point between the modules and the keyboard circuit board to make the connections.

This was all written up in the PPC Journal or one of its worthy successors but I don't recall the issue. In my case, I just updated my '41C by replacing the RAM chips with those for the '41CV but that's another story (in this Forum's archives).


Jims absolutely correct, how many did you do Jim?

I have to clean up my solder skills. Interestingly enough, the time module does NOT take over the ROM assigned PORTS on the CL.

So physically having the timer in port 3 (my configuration) still allows without conflict the MATH and ADV rom to reside there also.

When I cat 2 the calc I get the following:

C PPC 1981

Not bad EH?

Edited: 17 June 2011, 6:53 p.m.


The Time Module can reside in any Port, without conflict. This is because the Time ROM uses Page 5, which isn't physically addressed via a Port. In the CL the Time ROM is internal, in the Flash on the CL board, and the ROM in the physical Time module is never accessed. This is accomplished by preventing any address in Page 5 from appearing on the 41 address bus.

You could put the timer portion of the Time Module inside the calculator body, but what's the point? The Ports are now only really needed for things like the card reader, printer or Wand, so three open Ports should be sufficient.

As far as the Clonix, you still need to be careful to make sure that you don't virtually plug a module into the addresses being used by the Clonix, because a bus conflict will result. Remember that the Clonix uses addresses programmed into the module, (AFAIK) as opposed to physically decoding the Port address where it resides. This is probably why certain configurations weren't working for you, Geoff. You should just as easily be able to virtually load those images into Ports without using the Clonix, unless it is doing some kind of bank switching that I don't know about.


Hello Monte

Yeh, had to remove clonix as it did conflict. While testing last night and today, I realized only parts of the CCD and PPC were loading. That occured no matter which physical port was used. Also it dropped the third full page rom image completely whenever a port after the physical port it occupied was used for a rom image. And, whenever plug or unplug was used the Clonix was dropped completely and had to be removed and reinstalled.

The convenience if it worked is that it contained three full page rom images in one physical port. Now I understand more of how it maps to the logic pca.

So everything functions as perfect using the cl rom images for CCD and PPC. That leaves 3 other free ports available for one full page rom or 3 half page roms.

Well it is really easy to right a routine which can be dedicated to plugging and unplugging images in the three remaining free ports. Problem is most of my programs use CCD and PPC subroutines so they must stay resident.

As I said above, it is easy to automate the swapping of images with a dedicated key assigned routines.

Thanks again Monte!


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