HP41 / SY41CL Mini-B USB Power Connector (Module)


Inspired by Kerem, and Diego, and Frido (OK, Yes, I COPIED Diego and Frido's ideas! ;-), I used a Mini-B (5-pin) USB adapter and a 41 memory module housing to make a USB power connection/module for my 41CL today. Although it doesn't save a port like Kerem's solution, I wanted to have a "portable" means of powering up some other 41s I have around (since I regularly find myself without N-cell batteries when I need them).

Disclaimer: First of all: My photography skills are horrible - I'll never pretend be a Dave Hicks or Geoff Quickfall. Second: This sequence of photos and information is purely for entertainment purposes. If you (foolishly?) attempt to replicate the details below on your calculator (note: some details were purposely left vague), I will not be held responsible if anything detrimental happens to your property. All the pinout information for this project is freely available on the web. (Besides, I Cannot be held responsible, as I have no money - I have a family instead! :-).

[Fig.1] Because I would be experimenting (and because they were inexpensive), I bought two different styles of USB adapters from an <awesome!> local cable store. One Mini-B socket had a "shroud" (left) and the other one didn't (right). I ended up destroying the left one (learning experience), so the right one was used for my connector, but I also used the shroud piece from the left adapter:

[Fig.2] First I took the 41 memory module apart. I used solder-wick to unsold the memory chip from the solder-pads. I *thought* I would be using the perf-board but didn't need it after all (once I discovered that I would be able to use the wires inside the USB adapters).

[Fig.3] This is the "guts" of the adapter that later got destroyed. The pic serves to show that the black outside plastic (actually rubber) adapter housing can simply be sliced length-wise and removed. The white/clear center area between the USB connectors is fairly soft - I think it's just hot-glue-gun glue. I saved the black shroud at the Mini-B end and nothing else.

[Fig.4] Once I cut away enough material from the second USB adapter ([Fig.1] right side), I was able to access the individual wires. I plugged in a USB power supply and located the "+5V" and "gnd" signals. They are the extreme "outside" pins on the Mini-B connector. I then cut the three unused wires flush where they came out of the clear material.

[Fig.5] This pic shows the Mini-B connector wires soldered to the (former) memory module solder pads (per Diego's and Frido's links above). The right side of the pic shows that the bottom-half of the housing has been "notched" to accept the USB connector.

[Fig.6] Parts placed back into lower half of memory module housing. The shroud will cover the "exposed" metal bits (as our UK friends would say ;-) on the Mini-B. Almost done.

[Fig.7] You have to test it again, right? Note: Paper plates come in handy so you don't scratch wifey's table.

[Fig.8] New USB power module plugged into the 41CL. Before taking this photo, I first turned on the 41CL and started the clock, then plugged in the USB power supply (no smoke!), then removed the 4 N-cell batteries and the clock remained running (hard to see in pic). Yeah!

I haven't glued the module housing back to together yet. Should I use the Polystyrene cement that Randy strongly recommends, or is there something more forgiving, like rubber cement, in case I need to get back into the housing? Note: The original factory "bond" was only at the interface of the top and bottom housing halves (no clip retainers used in here).

Thanks again guys for the inspiration. I would be remiss if I didn't tell Monte THANK YOU for his great contribution in his spectacular 41CL board!.


Edited: 7 July 2012, 2:32 a.m.


Matt this is a super nice article, I´m sure will set the basis and that others (more skillful than myself) will follow suit '- thanks for sharing it.

One thing that occurred to me inmediately was: any chance to also use the same port for the serial connector as well? Doesn´t look possible but maybe you can come up with a creative idea for that too.





I originally planned (maybe still plan) to combine the USB connector and the serial port connector into the same module housing (I left room for it), but the existing 2.5mm stereo Jack is unfortunately too long for the module (some of the module's gold bus contacts would have to be cut away to provide enough depth/clearance, as it is nearly as deep as the module). I need to see if a shorter Jack is available. Monte probably had good reason to use the one he selected. My guess is that it most likely had to do with the module covers he had manufactured (least cost & most simplistic means) to provide the most depth possible inside an unused port, so his choices wouldn't be too limited.

One thing about the female mini-B USB connector.. If a person wanted to make a lower-profile connection or didn't want hack up a USB adapter, they should probably locate a "vertical DIP" style connector. This simply means there are real pins that you can solder to, and they come straight out the back. The other styles are "90-degree DIP" and, of course, the biggie SMD (Surface Mount Device), which, in terms of mini-B connectors, are the majority in use in most consumer products, but are really not feasible here due to (most of) our human soldering limitations. I just realized I don't need to explain this stuff to us, the techno-geeks here, do I? The USB adapters I cut apart have "vertical DIP" connectors, but I didn't want to cut back too far into the white/clear material to access the pins (that's how I destroyed the first adapter), so I just cut back enough to gain access to the wires that were already soldered at the mini-B end.


Edited: 7 July 2012, 11:20 a.m.


Hi Matt,

Your solution seems both, elegant and functional; and on my behalf you are free to be inspired by, copy, improve, etc... any of my ideas to power the HP-41... ;-)

From a very personal (and somehow interested) point of view, the main drawback of such power solutions (mine also) is the use of a module shell and connector which could have find a more "productive" usage. (housing one of my Clonix, NoV's or USB41 -with power! :-)

The lack of housings/conectors is still the biggest problem for me.

Just in case anyone is interested I'd gladly trade some module doubling jobs just to keep the remaining housing: (2 x X-MEM, 2 x Mem Modules, X-FUN + X-MEM, or whatever other combination)

Regarding the combined serial/power module; this is possible of course, but with some type of surgery to the I/O port-connector-slot, not for the faint-hearted... :-)

Keep up the good job.


Edited: 7 July 2012, 2:09 p.m.



Thanks for sharing your thoughts on the scarcity of module housings and the I/O connectors (there's a saying: "rare as hen's teeth").

I'm sure somebody has considered 3D printing, which may be feasible for the housings themselves, but not for the I/O connector piece which would require manufacturing the gold contacts, a jig to hold them, then forming the plastic around the middle of the contacts. This is neither a simple or inexpensive task, is it? Hmm.


Edited: 8 July 2012, 2:49 p.m.


Hi Matt,

Regarding the 3D printing (or any other moulding process) I made a SketchUp 3D render on the CMT module housing (top and bottom halves) but, as you've pointed out, this is useless whithout a suitable source for the connectors which I don't consider feasible at all.

However, for my own USB power cable I built a "custom connector" (just handicrafted and glued into a not-very-well-looking module housing) with an RJ-45 female to female adaptor. Just to save one I/O connector.

All the best from Dominican Republic.


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