A low-cost uninterruptible power supply for your broadband Wi-Fi router using a USB battery bank and a 5 V to 12 V DC boost cable (~1 EUR from AliExpress). Keeps your router running through short power outages so you don't lose calls or downloads while the backup generator kicks in.
USB 5 V to 12 V boost cable — the black housing contains an MT3068 converter PCB.
Inside the housing — MT3068-based boost converter.
This cable provides up to ~8 W output, which is enough for a standard broadband router. If your router draws more than 8 W, look for a higher-capacity boost cable.
Setup
Connect a 5 V DC adapter to the battery bank's charging port. The battery bank's USB output feeds the boost cable, which powers the router at 12 V.
Complete setup — 5 V adapter charges the battery bank, which powers the router through the boost cable.
Backup duration depends on the battery bank capacity. A smaller battery handles short outages (a few minutes while a generator starts); a larger one extends runtime for longer outages.
How to turn a ~5€ A5-V11 pocket router into an XMPP chat-bot that lets you remotely access and control your home network from a smartphone — no port forwarding or dynamic DNS required.
Why the A5-V11?
In the quest for the cheapest off-the-shelf Linux hardware, the A5-V11 pocket router stands out — it consumes just ~0.3W, making it ideal for always-on IoT applications.
CPU
360 MHz MIPS (Ralink RT5350)
RAM
32 MB SDRAM
Flash
4 MB
Ethernet
100 Mbit
Wi-Fi
IEEE 802.11b/g/n
USB
1 port for peripherals
LEDs
Red and blue status indicators
The A5-V11 pocket router — a ~5€ Linux device consuming just 0.3W.
How it works
The custom a5v11-xmpp firmware strips down most router/Wi-Fi functionality to fit an XMPP chat client daemon (based on lib-gloox) that acts as a chat-bot. XMPP makes it easy to access your home network without tweaking your home router settings — no port forwarding or NAT configuration needed.
Keep this device connected to your home internet and "chat" with it from anywhere using the Xabber app on your smartphone.
Setup instructions
Step 1 — Create two XMPP/Jabber accounts (master and slave) on your favorite Jabber server as explained here. Add both accounts as friends so the XMPP server can pass messages between them.
Step 2 — Connect a CAT-5/6 cable between your PC and the A5-V11 router, then power it on.
Step 3 — Flash the stock firmware with the a5v11-xmpp image. Follow the step-by-step guide in this blog post (also see the OpenWrt wiki for general instructions).
Step 4 — Connect the A5-V11 router to your home router's network (internet).
Step 5 — Log in via SSH to host my-a5v11 (user: root, default password: brb0x).
A compact, battery-powered IoT device built from a Raspberry Pi Zero, a Huawei E173 USB 3G modem, and a prepaid SIM card. RBox — a lightweight Buildroot-based Linux distribution (~25 MB) — boots from the SD card, connects to the internet over 3G, and runs an XMPP chat-bot so you can monitor and control the device from your phone's chat app.
Compact stacked setup — Pi Zero, USB 3G modem, and 5200 mAh battery pack.
What happens at boot
usb_modeswitch switches the 3G modem from mass-storage mode to modem mode
umts-keeper + sakis3g establish and maintain the 3G internet connection
The XMPP chat-bot daemon (built on gloox, a C++ XMPP library) logs in to a Jabber server
You can now communicate with the Pi Zero from your Android Xabber app (or any XMPP client)
Features
Total cost under ~50 EUR (Pi Zero + SD card + 3G stick + SIM + battery)
Read-only root filesystem — power cuts do not corrupt the SD card
Over-the-air Linux image upgrade via XMPP chat message (~25 MB per upgrade)
No cloud service, port forwarding, or dynamic DNS required — just two Jabber accounts
Send/receive SMS and dial USSD codes via chat messages
Control GPIO pins with get/set commands
Execute shell commands remotely via chat
Multiple XMPP accounts can control the same device simultaneously
Use cases
SMS gateway — deploy at home with a local prepaid SIM, access SMS from anywhere via Jabber
Weather station — deploy in a 3G coverage area with solar panel and sensors
Fleet management — place in vehicles with a GPS sensor, track from a central PC
Wildlife monitoring — deploy with a camera in a GSM-covered area
Digital signage — control display content remotely via chat
Anti-theft tracker — for cars, boats, caravans — sends GPS coordinates when movement is detected
Home automation — monitor temperature/humidity, control relays via GPIO
FAQ
How much 3G data does this use?
With no chat traffic, only XMPP heartbeat packets are sent — typically a few hundred kilobytes per day.
How long does the battery last?
A fully charged 5200 mAh battery keeps the setup running for 8–10 hours. Use a higher-capacity battery for longer runtime.
Can I deploy this off-grid?
Yes, with a larger battery and solar panel. Ensure the location has 3G coverage.
What happens if power fails during an OTA update?
RBox writes the new image to the non-active partition, then flips the boot flag and reboots. A power failure during the write leaves the active partition untouched.
Why the stacked form factor?
A compact rectangular brick is easier to enclose in a 3D-printed case than dangling cables.
Old setup (left) vs compact stacked setup (right).
How much does this cost to run?
Total hardware cost is under 50 EUR. A 100 MB / 30-day prepaid data plan (e.g. ~2 EUR/month with Congstar in Germany) is sufficient for basic I/O control and command traffic.
Write the image to the SD card using Win32DiskImager or similar
Remove and re-insert the SD card — a boot drive appears
Create xmpp-login.txt on the boot drive using this template — replace the sample credentials with your device's XMPP username and password (update APN details for your carrier)
Insert the SD card into the Pi Zero and power on — wait 2–3 minutes for the 3G modem LED to glow solid blue
On your phone, open Xabber and log in with the master XMPP account
The Pi Zero should appear online — send Help to see the list of available commands
Send Sysupdate;reboot to update to the latest RBox image — see the full command reference
For graceful shutdown, send poweroff and wait for the 3G modem LED to turn off
