FitzChivalry
Posts: 3
Joined: Sun Jul 02, 2017 11:22 pm

Possible to use RPi to share cellular internet with 6 devices w/o using a hot spot?

Sun Feb 18, 2018 1:26 pm

TL;DR

I need to share an Internet connection from a cellular device with six non-cell-capable tablets for FIRST Robotics Competition regional events. Hotspots are not allowed at the venue due to conflicts with the Field Management System. Can a Raspberry Pi 3B be used to accomplish what I need?

Backstory

My team developed an Android-based scouting app. The back end for the app in 2017 was Firebase. To use Firebase, you need an Internet connection. Because wifi hotspots conflict with the Field Management System (the system that enables the human drivers to interact with their robots) we used two cell phones and Internet-over-Bluetooth to get the six tablets online.

Unfortunately, the Bluetooth connections had a tendency to drop during heavy use, and with no notification. So, our scouts would be recording details about the match, but the data wouldn't make it to Firebase. This was especially problematic at World Championship, where we had to fall back to using paper forms to collect data.

We'd like to replace Internet-over-Bluetooth with a more-reliable option for the 2018 season. Our first competition is in less than two weeks.

I am proficient with computers, but my networking knowledge/skill is mediocre. I'm hoping to find a tutorial that will help me get things set up without requiring that I learn a lot (due to the 2-week timeframe).

Planned implementation

We have six Samsung tablets that we use to host the Android app. We also have a cellular tablet that will be providing the Internet signal to the devices. We have a RPi 3B. I bought USB-to-Ethernet converters for each tablet, a USB-powered 10/100 8-Port Switch, Cat5e cables, and a couple of 16750 mAh external batteries to power the RPi and switch.

The plan is to use USB tethering to provide Internet to the RPi (this part has been successful), and then to share that Internet with the six tablets via that network switch (this part hasn't been successful, yet).

What I've already tried

I've tried following various tutorials to set up DHCP on the RPi at a static address (these are just a few of the articles I read):
  • [HOWTO] Rasberry Pi as a wired router with webmin as web ui (link)
  • Setting up a home network DHCP/DNS server with dnsmasq (link)
  • Lesson 3 - Dynamic Host Configuration Protocol (DHCP) (link)
  • Setup Raspberry pi as a dhcp server (link)
None of these quite worked. I could get DHCP running using static addresses on the RPi, but couldn't get the RPi, itself, to pull the static IP address assigned to it. It would still have 192.168.0.2 listed as its IP, when it should have moved to 192.168.0.10. Note that all of these tutorials seem to assume that there was a router upstream from the RPi, which isn't the case in my current configuration, since upstream is the cellular device.

As I went through the tutorials and various articles, I learned more, so if someone tells me I'm on the right track and that one of these tutorials is worth another shot on a clean install, I'm totally game. I'm just trying to not spend my time chasing an idea that isn't likely to lead to success.

I'm open to any and all feedback. Is my idea wrongheaded? Am I going in the right direction, but just haven't hit the right tutorial? Am I missing a piece of equipment?

On behalf of my sanity and my team, thanks in advance for your help!

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topguy
Posts: 4743
Joined: Tue Oct 09, 2012 11:46 am
Location: Trondheim, Norway

Re: Possible to use RPi to share cellular internet with 6 devices w/o using a hot spot?

Tue Feb 20, 2018 12:32 am

Can you assign static addresses to the tablets with usb2eth ? Wouldnt that be better to avoid having them potential switch IP addresses ?

But in general you are trying to set up a hotspot, the only difference is that interface "ppp0" (modem in a normal 3G hotspot) will be "usb0" for your tethered tablet (I'm guessing) . And instead of sharing on wireless "wlan0" you are sharing on cabled "eth0".

I would also consider buying a 3G/4G modem instead of using the tablet, then you would be even closer to a standard setup. I have never tried to tether an Android device on Linux so I dont know if there are some pitfalls there for your setup.

Also drawing a "picture" and naming the interfaces and which IP-address you have/want on each of them is also helpful.

FitzChivalry
Posts: 3
Joined: Sun Jul 02, 2017 11:22 pm

Re: Possible to use RPi to share cellular internet with 6 devices w/o using a hot spot?

Sun Mar 04, 2018 10:08 pm

Circling back around on this, I took the advice offered in a couple of different forums, and ditched the RPi and went with an inexpensive Acer router, instead. It ended up being cell device -> USB cable -> router -> Cat5 cable -> switch -> Cat5 cable -> Ethernet-to-microUSB converters -> tablets. This enabled each of the tablets to push data to/pull data from Firebase.

While it worked well this weekend at the Palmetto Regional, we're going to look into using Bluetooth next season, at the same time as replacing Firebase with MongoDB + NodeJS running on a RPi3.

My thanks to @topguy for the helpful advice!

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