Show HN: Hacking a $20 4G wireless hotspot into a texting device

209 pointsposted 5 days ago
by bobili1234
(bkovac.github.io)

37 Comments

notpushkin

5 days ago

This is really nice! It so happens that I’ve just bought a $10 4G dongle [1], guess I’ll have to check what’s inside now :-)

[1]: like this: https://img.joomcdn.net/ea91b4418997d83d802339fad0bbcf878b9d...

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Aside, but it appears some MSM8916-based dongles run Android UI despite having no display: https://github.com/u0d7i/uz801#screenshots

kotaKat

5 days ago

I did some funny software porting on one of those dongles. At one point, I had it connected to a battery pack for power, joined onto my home WiFi for LAN/WAN access... and had the stick running the Open5GS cellular core stack, allowing my CBRS LTE base station to serve users on an in-home private LTE network by connecting to the cellstick over WiFi for management. (No, the stick's own cellular modem wasn't being used here at all. Just scavenged compute for the tiniest LTE core!)

So... so cursed.

djfergus

4 days ago

Postmarketos works well on those and they have lots of info and links. [1]

My biggest tip is to carefully back up every partition of the original firmware - there are many many seemingly identical variants and if you hose your particular baseband components you will lose your cellular functionality.

[1] https://wiki.postmarketos.org/wiki/Zhihe_series_LTE_dongles_...

untitaker_

5 days ago

it's most likely UZ801 (mentioned in the article)

notpushkin

4 days ago

It’s a weird one!

  [ro.build.description]: [msm8916_32_512-userdebug 4.4.4 KTU84P eng.huanghonghuan.20250226 test-keys]
  [ro.build.sw.custom.version]: [UFI003S_V03_ZX_DD_250226]

walrus01

5 days ago

Based on the work the person has done, if they wanted to make something with an exceedingly long battery life, and the battery setup there already seems to be basically a 1S li ion, they could graft in a back side battery holder for two high quality 18650 cells in parallel. It would probably last weeks.

iamnothere

5 days ago

A 10000mAh pouch battery would take up less room and provide more battery life. They are almost as cheap as 18650s too.

walrus01

5 days ago

The neat thing about 18650s though is that you can put a battery door on it and make them swappable, if a person used a holder that can accommodate button top protected 18650 cells. The same cells can also be shared by a bunch of good quality flashlights and headlamps. I have several extremely useful headlamps from "sofirn" that take my choice of cell and have a built in USB-C charging port and charge circuitry protected behing a gasket and twist-open ip67 sealed cap. The pouch battery would be better as an integrated all in one product but also makes the thing a bit less modular.

iamnothere

5 days ago

There are advantages in some applications, it’s just not a one size fits all tool. Slim devices aren’t really a good fit for them. They make sense in round devices (like a flashlight) or larger devices where space isn’t as much of a concern.

DANmode

5 days ago

Thank you to both solder-nerds for contributing strongly to the thread, please don’t fight.

walrus01

5 days ago

No fighting intended, I think it's interesting to see that there's many ways of doings things, and doing a sort of mental whiteboard exercise on what the benefits and drawbacks of different things are... Like, using cylindrical cells would let me share cells with my head lamp, swap cells, independently charge cells and keep spare charged cells ready.

While using a pouch cell keeps the profile much more slim, portable, still has opportunities for really high capacity in watt hours, and allows for a more robust case design that doesn't have the structural weakness of a battery door.

And if you put the pouch cell on a set of wires with a small pluggable connector to the main PCB (and a case that can screw open/shut) it's still an item the user can replace with 5 minutes and a screwdriver if it wears out from many cycles over a period of years.

iamnothere

5 days ago

> And if you put the pouch cell on a set of wires with a small pluggable connector to the main PCB (and a case that can screw open/shut) it's still an item the user can replace with 5 minutes and a screwdriver if it wears out from many cycles over a period of years.

True, and you could even enclose it in a quick swap hard shell case with contacts, like the old Nokia cell phone batteries. (Those are actually still good for some uses, I have a gadget that uses them.)

We’re fortunate to live in an era of battery abundance.

jsisto

5 days ago

How is a 10000mAh pouch more energy dense than an 18650?

bri3d

5 days ago

By not having void air space in between cylindrical cells like you'd get with two 18650s? It's mostly just a matter of packaging.

Pouches can be made to have better volumetric density than cylindrical cells quite easily, which is why laptops aren't generally full of cylinder cells anymore; the challenge is just providing them enough external support/compression and swelling allowance, which can be accomplished through chassis design.

iamnothere

5 days ago

Pouch cells are lighter per mAh due to the lack of metal casing. But more than the casing, the form factor is better for a pocketable device. The cylindrical form factor sticks out, usually wastes some space, and can’t be neatly tucked behind a board or display.

harhargange

5 days ago

I often ditch my phone and carry my hotspot device for my internet. The only drawback is that for viewing my texts and OTPs i end up putting the sim in my phone or opening up the web interface on my laptop. This seems to work very well as a dumbphone per se.

newhotelowner

5 days ago

How do you check sms/OTP/text using web interface on your laptop?

notpushkin

5 days ago

This probably depends on your particular dongle model. Back in 3G era, some carriers offered USB modems with SMS locked out in the firmware, but you could flash a firmware from a different operator (also install their variant of software, the only difference being the added SMS tab and a different skin) and then you can text and even use USSD! (No calls, though.)

harhargange

5 days ago

yeah my vendor's dongle has this specific feature. A light also turns ON on the modem when SMS is received.

blobbers

5 days ago

If you move to an Apple set up, the phone can act as a hotspot and there is no need to take out your sim. Also... you have a physical sim card? I thought those became obsolete.

toast0

5 days ago

Physical sims are as obsolete as 3.5mm headphones. They both continue to work and have different tradeoffs than 'modern' alternatives and you have a different selection of devices to work with.

EvanAnderson

5 days ago

Thanks for coming up with a very apt analogy. I wanted to reply but couldn't come up with something I felt good about.

xx_ns

5 days ago

This is a really cool project! A mini cyberdeck that doesn't seem too impractical to use. Repurposing the Clicks keyboard is a genius idea.

msm8916

5 days ago

OpenStick is super old though, there are Linux and OpenWRT builders that track the upstream kernel, check hkfuertes and others.

ACCount39

5 days ago

Oh, if it isn't the MSM8916 himself! Fancy seeing you out there in the wild - posting on HN no less!

Is there a guide for cheap MSM8916 platforms you would recommend? There is a hkfuertes repo, but the one I found is archived. Not to say it doesn't work, but that doesn't instill much confidence.

VinnyBarreca

5 days ago

It would be pretty cool to put Hermes Agent or some agent system on that thing, assuming the OpenStick build has enough RAM/storage. That would be fire.

ACCount39

5 days ago

What it has at its core is a smartphone chipset from 2014 - MSM8916 or so. Not exactly an AI compute powerhouse.

RIMR

5 days ago

Truly, I couldn't imagine a worse platform to put a coding agent on. What even would be the point?

It's got less than 512GB of RAM, no package manager, and virtually no storage.

DingleDodies

5 days ago

This is cool and all, but what is the point? I have a feeling it could be useful for me but what is it really for?

dgf18

5 days ago

Really cool!

catidegla

5 days ago

One layer down from where this thread is looking: the SMS never lives in the Android userspace on these sticks. It sits in the modem's own store, either on the SIM or in modem memory, and the vendor web UI is just a thin thing reading it out of there.

So you don't need a messaging app that still runs on Android 4.x. If the device exposes an AT port, AT+CMGF=1 then AT+CMGL="ALL" dumps everything, and AT+CPMS picks which store you're reading. On the Qualcomm ones that keep the AT port hidden behind QMI, libqmi reaches the same thing through the WMS service.