Installing modules in a HP41C


Hi, I'm thinking of installing one or more of my modules (perhaps the xtended memory) inside the 41C to make room for a Clonix module. Or perhaps the best is to install the Clonix internally (once a bootloader is incoporated). I've not been able to find any literature on the technique.

Is it as simple as opening the module and the HP41, and soldering the connectors together? Is there enough room, or is some surgery needed? Any pitfalls?

Diego, Do you have any plan to sell the bare boards?




Hi Dave,

You can find info regarding how to install modules into an HP-41, on some PPC Journals. I'd like to be more precise but it's too much time since I placed my Quad Memory into my 41C guts... ;-)

Anyhow, I remember I only made some thin wire soldering and place the Quad board inside a narrow space beside the battery compartment. Some others with more recent experience will sure be of much better help.

Regarding the Clonix part of your message:

I'm not planning to sell bare Clonix boards as I'll have no way to test its functionality. Anyhow, I can't see a feasible way to implement the said BootLoader's needed hardware (please take a look at Clonix hardware info to make yourself a picture: 24 x 13 mm PCB...less than half square inch!), furthermore, if such Bootloader is implemented (on an oversized board, inside the HP-41 guts), an external connector shall be needed to face the re-programming tasks.

Which kind of connector pair (male-female) would be used??

There are really very few 41'ers ready to open, solder, drilling... into their loved 41's... not a general solution indeed. I think Clonix is intended to serve as a solution to as much users as possible, keeping the module shape, the calc shape, without intrusive surgery, with a cheap and easy to find programmer.

Oh! I almost forget a small point... Should the Bootloader portion of the PIC code becomes corrupted (whatever the cause)... there will be no way to recover the module (or the calc provided you built the Clonix inside it) but re-openeing it and re-programming it again in the same (traditional) way Clonix is already doing...

Any good idea (with drawings, PCB's layout and fully documented, will be greatly appreciated not only for me, but for the whole 41'ers community...;-))

Please don't misundertood me, Bootloaders are an amazing possibility of an amazing device, namely, the PIC's microcontrollers, but there are many reasons, to my eyes, for which this particular feature is innapropriate in this particular case.


P.S. On the contrary of what has been published in other PIC related forums, I have never seen a single 18F252 PIC with Factory pre-loaded Boot-Loader, all of them come programmed to all zero's. (Erased state is all one's).


Hi Diego,

I agree, the serial programming option makes a bootloader unnecessary--it uses less code, fewer parts, is more reliable, cheaper, easier to build, and programming via the connector is much cleaner than a separate connector for a 2-wire serial jack/plug. It's a very nice, clean design as is.

If there were ever any need for a serial bootloader, perhaps it may be accomplished by putting the max1380 or diode/resistor on a similar adapter board, taking power from the serial line (or a power jack), and placing the "serial in" and perhaps a "bootload enable" logic line to two of the three currently unused connector pins; if "bootload enable" is asserted at powerup, then the bootloader is enabled, otherwise they are ignored, and clonix is started. At any rate, anyone with a clonix in need of a bootloader could experiment with such an approach by adding a couple of jumper wires. I suppose the choice would depend on the powerup behavior of B3, B4, and F1.

As I mentioned in the original post, the aim of my question was really to install the quad memory, to free up a module case for the clonix :-)

Thanks, and regards,



Installing modules inside a 41C is not really a big deal, if you have a steady hand and the right soldering tools. And if course if you are willing to risk your machine. My advise would be to get hold of a 41CX, so it has everything you want. Maybe add to XMEM module inside, but there is really not muchmore you could want.

In case you really want to start building, you will have to look at some old PPC issues. Pictures of how it looks are in my own museum:, follow the link to Meindert's Museum.

The wires to the modules are very thin wires soldered to the correct traces on the pcb.


I have an HP41CX with two internal XMEMORY modules. Apparently HP sold unpackaged and uncut sheets of XMEMORY modules to somebody, because these are two genuine HP circuit boards (without connector) that were never cut apart. They are hand wired together and then wired to the keyboard.

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