Hi again yyzkevin,
I let my imagination loose and made a quick 5 minute 3d model of "The Imaginary Penultimate Expander" for the 200LX 😉
This would be a device that slides into the PCMCIA slot on the left of the HP Palmtop, similar to those Amiga 500 hard drives that attached on the left of the A500.
The PCMCIA card that goes into the Palmtop hold the device in place (hopefully), and multiplexes the PCMCIA bus to the 2 card slots and all the other features inside,
so to the card services, it just looks like a large bunch of PCMCIA cards...
I tried to put everything a DOS Palmtop user would ever need into one expander device,
it's way too optimistic though, I don't think its possible to build something like this at the small size of the expander in the images,
it would have to be larger, and have less functionality/connectors to be buildable and affordable 😉
But it's a great "target" to try and design and build something as close as possible to it...
It could also be built to work in other machines too, besides DOS HP Palmtops...
Although it's a very quickly built and crude 3d model, the dimensions of everything are correct, i looked up all the dimensions of the 200LX, PMCIA cards, CF card, etc...,
except for the DB25 and DB9 ports, I eyeballed those from a photo, and I think they are a tiny amount too large...
Wireframe isometric top view with text labels
This penultimate device has:
* 2 PCMCIA slots, for 2 Type 1 or 2 Type cards, or one Type 3 card (which is too thick to allow for 2 Type 3 cards so it fits into the bottom slot and takes up both slots)
* a headphone 3.5" stereo jack on the front, and a 3.5" stereo line out jack on the back. These could be connected, for example, to an internal opl3 and/or some buffered digital audio chip inside, or simply a COVOX clone on an additional parallel port.
* An extra DB-9 RS-232C port as COM2, which is connected to a UART in a straight fashion, unlike the palmtop's built-in COM1 port and cable, so you don't need a null modem adapter and can connect a serial mouse directly to the COM2 port.
* A D25 parallel port as LPT1
* a female RJ-45 socket, connected to a 10Mbps PCMCIA LAN chip out of a PCMCIA network card that's supported by the 200LX.
* a CompactFlash card slot on the front capable of using standard (up to 32/64 MB), or, up to 2GB cards with the acecard3 driver.
Power is provided through a USB Type-C connector at the back of the device.
All these features would be connected as PCMCIA devices on the PCMCIA bus, of which, I'm still not sure how many PCMCIA devices are supported on a PCMCIA 2.0 bus. (I need to do some further googling/searching for this information, and I hope it's more than 2 😀 🤣
But I have read that the PCMCIA 2.0 design is based on the 16-bit ISA bus, so I have a hunch it should support more than 2 PCMCIA devices and all the functionality in this unicorn expander might be possible, but in a bigger box 😀 🤣 ...
Anyway, this is just a purely fantastical idea that I don't think will ever be created, but it's a great design goal to try to build something resembling this with less functionality, but as close to it as possible...
I don't think it will be possible to cram all the necessary hardware into the size of this expander, so a real-world, realistic one would have to be a bit larger, or, features will have to be removed...
Actually, you probably won't be using the PCMCIA slots a lot of the time as nearly everything you would ever need is already provided in the expander...
For something more realistic, buildable and affordable, maybe just a device of similar size/dimensions, but just the following functionality:
* 2x PCMCIA Type 1 and 2, or 1 PCMCIA Type 3 card
* A DB25 LPT1 port at the back
* an opl3 chip (adlib compatible) with the headphones 3.5" stereo jack on the front and the line-out jack on the back to connect to a pair of speakers...
* a USB Type-C connector at the back for power.
* All the rest like CompactFlash storage, ethernet and/or an additional serial port can be done with cards in the 2 PCMCIA slots 😀
And, if there is any room left, maybe a small one-cell lithium-ion or lithium-polymer battery, that's charged by the USB Type-C power supply/regulator IC.
This doesn't need to be a big battery, just enough to power the unit for 2-3 hours would be a great start, something like a one-cell 1200mAh lithium-ion pack.
PS: https://lab.yyzkevin.com very cool, all in a browser window 😀 but it asks for a username after I launch the IBM classroom lan manager...