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A BEAT-UP OLD PHONE CAN BECOME A HOME SERVER THAT IDLES AT 1 WATT

An old phone has an octa-core CPU and gigabytes of RAM, and idles at 1 watt — Hardware Haven turned a beat-up one into a working home server.

by Hardware Haven

FULL CAD BOM FIRMWARE DOCS

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COMPAREE VERDICT

Hardware Haven took a beat-up Xiaomi Mi A1 bought for about 30 dollars on eBay, flashed postmarketOS, built a headless image, and ran Docker with Home Assistant on it. The result idles at about 1 watt and has run for days without dropouts, with 4 GB of RAM and 64 GB of storage, which is plenty for light services. To stop it living on a battery 24/7, he removed the battery and fed USB power through a diode into the battery leads. He is clear that this is not a tutorial: the bootloader, nftables networking and power issues took a lot of trial and error, and the written setup steps come from a separate postmarketOS plus Docker guide. If your phone is well supported by postmarketOS and you are comfortable with Linux and a soldering iron, it is a fun weekend reuse project; if not, the build stops at the device list.

GOOD TO KNOW

  • —No repository or files exist — this is a YouTube video demonstration by Hardware Haven, not a packaged project with step-by-step instructions.
  • —postmarketOS install process is documented on the postmarketOS wiki for 250+ devices, but you must confirm your specific phone model is supported before buying parts.
  • —The battery-removal and diode power mod is shown on video but not written up with part numbers or schematics.
  • —A separate written guide exists for clustering multiple phones into a k3s setup (blog.denv.it), but it assumes postmarketOS is already running.
  • —postmarketOS is GPL-licensed free software; the clustering guide appears under CC BY-SA 4.0.
  • —Hackaday covered the build in August 2025 as a proof-of-concept, not a polished tutorial.

Parts to buy

5 items

From our check of the build. Exact quantities and part numbers are in the creator’s BOM.

  • Old Android phone (confirm postmarketOS support first)Find
  • Diode (type and rating not specified in video)Find
  • Soldering ironFind
  • USB OTG adapter if not includedFind
  • 5V power supplyFind

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Can I build this?

Printnothing required
BuyAn old Android phone (confirm postmarketOS support first), a diode (type and rating not specified in video), soldering iron, USB OTG adapter if not included, 5V power supply
ToolsSoldering iron, phone disassembly tools, bootloader unlock capability (often requires manufacturer approval), computer running Linux for postmarketOS install, multimeter recommended for charge controller voltage checks
SkillsARM bootloader unlocking, Linux command line, basic soldering to charge controller pads, kernel module troubleshooting. Intermediate-to-advanced Linux experience required; this is not a first electronics project.
TimeA weekend if the phone is on the supported list and boots first try; a weekend-plus if you have to build a custom kernel or trace charge controller pinouts
Cost$ — old phones cost almost nothing if you already have one; the diode is pennies; soldering tools and USB adapters are the main cost if you do not own them
SafetyRemoving a glued-in lithium battery can puncture it — work slowly, never bend or pierce the cell, and recycle it properly. The phone expects 3.4 to 4.4 volts, so raw 5 volts USB is too much; check the voltage after your diode or buck converter with a multimeter before connecting. Disconnect power before soldering.

Build at your own risk. Projects involve tools, electronics and sometimes mains voltage — follow the creator’s safety notes.

Videos

I Turned This Broken Phone Into A Home Server

Proof-of-concept demo showing battery removal, diode power mod, postmarketOS install and Home Assistant running. Not a step-by-step tutorial.

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Gallery

blog.denv.it
androidauthority.com
img.youtube.com

Start here

Navigation into the creator’s own docs — we don’t rewrite the guide, we route you to the source.

  1. 1.Confirm your phone model is on the postmarketOS device list (Do this before buying any parts. If your phone is not supported or support is partial, the project stops here.)
  2. 2.Read the Hackaday coverage to understand what the build involves (This gives context but is not a build guide.)
  3. 3.Watch the Hardware Haven video to see the diode mod and boot process (Pause and screenshot the diode placement; there is no schematic.)
  4. 4.Follow the postmarketOS install guide for your specific device(This is where the actual install happens. Device-specific quirks are documented in the wiki.)
  5. 5.If clustering multiple phones, read the k3s guide after postmarketOS is stable (Written guide for running Immich and Jellyfin across several phones. Assumes postmarketOS is already working.)

Resources

Documentation, files and community threads for this build — we link straight to the original sources and never rehost the creator’s files.

KNOWN ISSUES

  • Buying a phone before confirming postmarketOS support. Many devices have partial support (no GPU acceleration, no cameras, no modem) and are listed as 'community' tier, which means basic features may not work.
  • Leaving the battery in a phone that runs 24/7 on the charger. The creator removed it for that reason, because a lithium cell kept permanently charged can swell; if your phone's battery is already swollen, handle it carefully and recycle it.
  • Soldering the diode without a multimeter check. If you wire 5V to the wrong pad on the charge controller, the phone is bricked.
  • Expecting the video to include part numbers or a schematic. It does not. You will have to identify the diode type and rating yourself.
  • Assuming the clustering guide is plug-and-play. It requires working knowledge of k3s, persistent volumes, and ARM container images.
  • Underestimating bootloader unlocking. Check your exact model: the creator accidentally bought a Mi 5X instead of a Mi A1, which needed a Xiaomi account and a 15-day wait, so he bought a second phone that unlocked directly through fastboot.

Will my phone work?

Only if it is on the postmarketOS device list. Check the wiki first. Even listed devices may have missing features like GPU acceleration or camera support.

Can I skip the diode and just plug in USB power?

Probably not. The creator says pretty much any modern phone won't turn on with the battery removed and only USB plugged in. His workaround keeps the battery's small controller board and feeds it from a USB cable through a diode, so the phone sees something close to battery voltage instead of 5 volts.

What diode do I need?

The video does not name the diode. Its only job is to drop USB's 5 volts into the 3.4 to 4.4 volt range a phone battery normally supplies, so a low-drop Schottky diode is the wrong choice. The creator himself calls his diode janky and says an adjustable buck converter set to about 4 volts is the smarter option; measure the output with a multimeter before connecting the phone.

How much does this actually save versus a Raspberry Pi?

The video does not compare it to a Raspberry Pi. The phone in the video cost about 30 dollars used, idled at about 1 watt and drew around 6 watts under a stress test. If you already own an old supported phone, the hardware is essentially free; the main win is reuse and very low idle power.

Can I run this 24/7?

Yes, if the phone is designed to run on continuous power and the charge controller accepts the diode mod. The video shows Home Assistant running, which implies it is stable, but long-term thermal behavior and flash wear are not tested.

Community builds

No community builds yet — be the first, we feature the best ones.

Discussion1

FROM THE COMPAREE TEAM

The video runs postmarketOS on a Xiaomi Mi A1, but postmarketOS support varies a lot by device. If you have an old Android phone in a drawer, what model is it, and have you checked whether it is on the supported list?

CompareeTEAM1mo agoedited

Practical notes from our verification: Hardware Haven's video says outright that it is not a tutorial. It shows a retired Xiaomi Mi A1 (Snapdragon 625, 4 GB RAM) flashed with postmarketOS and running containers, including the power problems he had to work around and a custom headless image. For actual setup steps, the video description points to a postmarketOS plus Docker guide on bryansplace.github.io. The Mi A1 has less RAM than an 8 GB Raspberry Pi 5, so the appeal is reuse and very low idle power, not raw specs. The biggest trap: many phones on the postmarketOS device list have only partial support, which can be fine for a headless server but needs checking before you start. There is no repository, BOM or schematic. Correction (4 October 2026): we re-checked this page line by line against the project's own repository, documentation and videos, and fixed errors in earlier versions.

Hardware Haven

Hardware Haven demonstrated the build on YouTube as a proof-of-concept for e-waste reduction. The video shows a working 1-watt home server running postmarketOS and Home Assistant on a retired Xiaomi Mi A1.

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