managed to get my money back by filing a dispute, i guess he didnt respond with any defense. took this long…
Guys, I had a wild idea! I was a bit annoyed that the modem takes up a valuable USB port, and also there are perfectly good SuperSpeed lanes sitting unused. Originally I wanted to put some kind of USB socket on the outside, but that would be hard geometrically, and also the modem takes up a significant part of the USB port power alottment. So Instead, I added a microSD reader (UHS-I with GL3224 chipset):
Of course this makes the design much tighter and I had to go 6 layer with via-in-pad. On the other hand, 2 of those layers are solid ground, so this should really not affect RF performance. There is a 4-port USB hub IC (so we could hypothetically also break out one of the extra port to test pads for some internal use), SS lines are pass-through to the reader. This is a non-standard topology commonly used by cheap Chinese USB hubs and it usually works.
Theoretically the reader should use USB2 only for initialization and enumeration and then switch to USB3 SS lines so it should not compete with the modem (which is USB2 only) for bandwidth.
Physically, with the GNSS antenna, space for inserting the microsd should just barely fit beside it. Without the GNSS antenna, the card would stick out quite a bit so one has to be careful to not break it.
It’s still quite WIP (available in microsd git branch).
What do you think? Useful or overkill?
Both? 
Useful in my opinion. I like having sd cards slots on laptops. Since they are there, I’ve taken to leaving a card there & having my backup routine use it as an extra backup location. Can never have too many.
But if it requires 6 layers and via-in-pads, won’t it add a good bit to cost? Due to that, it feels like overkill, unless it would just be an optional variant.
This might not be usable for that, due to the card sticking out (unless you opt for the GNSS antenna).
The difference in PCB fab cost is about 5$ in 5pc series. More cost would be in the extra components.
And of course the most expensive part is the prototyping, especially if the first try does not succeed.
It is optional kind of by definition. Both variants are open and if there is enough interest in the original variant (which I suppose there will be), there is no problem with ordering it. And if there is enough interest in the overkill variant (which would have to be prototyped and tested first), we can also try that.
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My (unsolicited) advice: focus tends to win. It’s better to get a simpler but complete thing out faster, learn as much you can from it, and then add complexity.
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i2clabs Josh? did you actually receive a unit? I have been looking everywhere trying to find out more about his LTE card, but it’s a ghost. he doesn’t even have a photo of it that I can find. I ended up ordering PCBs to make the serial card myself because people were saying he’s been inactive.
ordered one a year ago, never came in. hes left the discord and hasnt been on this site since december 24th 2024 it says so something mustve happened to him.
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Apparently not. It sticks out into the display by about 2mm.
Managed to fix that in the end but very fiddly.
Currently it seems that antennas are the main performance bottleneck. On strong signal (e.g. with direct line of sight to cell tower), I get 50/30 Mbps with my current setup, on weaker signal, esp. indoor, it can go as low as e.g. 15/0.25 Mbps.
Open to suggestions for better antennas and antenna placement.
But even in its current form seems practically usable and an improvement over a USB dongle sticking out.
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Some naive questions from someone unaware of how hardware works:
- is it possible to reuse existing wifi antennas?
- if not, is it possible to install additional inner antennas?
- No, Wifi and LTE occupy different frequency bands, wifi antenna that are optimized for 2.4GHz and 5-6GHz will perform poorly when used for LTE bands.
- Without any modifications to the laptop shell, the LTE antenna can only be installed within the expansion card slot (or poking out of the slot). If you are willing to drill a hole through the expansion card slot, then it is possible to run the antenna cable through to another part of the laptop, but installation will be difficult and it makes the expansion card not easily detachable.
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