Limiting Battery Risk On Repurposed Smartphones With PostmarketOS

February 1, 2026 by Lewin Day 21 Comments

PostmarketOS is a Linux distribution specifically designed for those who wish to repurpose old smartphones as general-use computers, to a degree. This can be a great way to reuse old hardware. However, for [Bry50], it was somewhat discomforting leaving the phone’s aging lithium battery perpetually on charge. A bit of code was thus whipped up to provide a greater measure of safety.

The concept is simple enough—lithium batteries are at lower risk of surprise combustion events if they’re held at a lower state of charge. To this end, [Bry50] modified the device tree in PostmarketOS to change the maximum charge level. Apparently, maximum charge was set at a lofty 4.4V (100%), but this was reconfigured to a lower level of 3.8V, corresponding to a roughly 40-50% state of charge. The idea is that this is a much healthier way to maintain a battery hooked up to power for long periods of time. There’s one small hitch—the system will get confused if the battery voltage is higher than the 3.8 V setpoint when switching over. It’s thus important to let the device discharge to a lower level if you choose to make this change.

It’s a neat mod that both increases safety, but keeps the battery on hand to let the system ride through minor power outages. If you’re new to the world of repurposing old smartphones, fear not. [Bryan] also has a tutorial on getting started with PostmarketOS for the unfamiliar. If you’re working on your own projects in this space, we’d love to hear about them—so get on over to the tipsline!

Smartphone App For Leftover Vaccinations

May 30, 2021 by Chris Lott 29 Comments

South Korea’s Disease Control and Prevention Agency launched a pilot program yesterday to minimize vaccination waste using a nationwide smartphone app. People who are over 30 years of age can search for leftover doses on their smartphones. If any are available, they can book an appointment immediately within the app, and then get to the medical center within hours to receive the injection. One can tag up to five nearby inoculation centers to receive an instant message when a dose becomes available.

These leftover doses arise from people who have missed their appointment, but also just as you would expect when considering the short shelf life of the opened vaccine, the number of doses per vial, and modulo arithmetic. Within hours of the program rolling out, people began complaining about server problems and the lack of available doses. But this is a pilot program, after all, so some glitches are to be expected.

The full program is supposed to begin on June 9th, although it isn’t clear how it will be different from the pilot project, other than presumably having fewer bugs. The lead picture above shows the availability of leftover vaccines in central Seoul this morning — zero (the symbol 없음 means “none”). But the system does indeed work and people received vaccinations yesterday utilizing this program.

Technically speaking, this isn’t a new app, but rather, it is integrated into the two most popular South Korean portal sites. Anyone already using KakaoTalk or the Naver portal on their smartphone can use this leftover vaccination service with just the press of a few icons. Are the health authorities in your region utilizing smartphone apps or online reservations sites to distribute these leftover doses, doses that would otherwise be discarded? Let us know in the comments below.

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5G Power Usage Is Making Phones Overheat In Warm Weather

July 21, 2019 by Maya Posch 52 Comments

As reported by ExtremeTech, the brand new 5G network is running into a major snag with mobile devices as Qualcomm 5G modems literally cannot handle the heat. After just a few minutes of use they’re going into thermal shutdown and falling back to measly 4G data rates. Reports by both PCMag and the Wall Street Journal (paywall) suggest that 5G-enabled phones consistently see problems when used in environments where temperatures hit or exceed 29.5 °C (85.1 °F).

The apparent cause is the increased power draw required by current 5G modems which make heavy use of beam forming and other advanced technologies to increase reception and perform processing on the received data. Unlike 4G and older technologies, 5G needs to have multiple antennas (three or more) to keep a signal, especially when you grab your shiny new smartphone with your millimeter-wave blocking hands.

The spin-off from all of this seems to be that perhaps 5G technology isn’t ready for prime-time, or that perhaps our phones need to have bigger batteries and liquid cooling to keep the 5G modem in it happy. Anyone up for modding a liquid cooling loop and (tiny) radiator into their phone?

Test Ideas Now With Sensors Already In Your Pocket

March 20, 2018 by Roger Cheng 15 Comments

When project inspiration strikes, we’d love to do some quick tests immediately to investigate feasibility. Sadly we’re usually far from our workbench and its collection of sensor modules. This is especially frustrating when the desired sensor is in the smartphone we’re holding, standing near whatever triggered the inspiration. We could download a compass app, or a bubble level app, or something similar to glimpse sensor activity. But if we’re going to download an app, consider Google’s Science Journal app.

It was designed to be an educational resource, turning a smartphone’s sensor array into a pocket laboratory instrument and notebook for students. Fortunately it will work just as well for makers experimenting with project ideas. The exact list of sensors will depend on the specific iOS/Android device, but we can select a sensor and see its output graphed in real-time. This graph can also be recorded into the journal for later analysis.

Science Journal was recently given a promotional push by the band OK Go, as part of their OK Go Sandbox project encouraging students to explore, experiment, and learn. This is right up the alley for OK Go, who has a track record of making music videos that score high on maker appeal. Fans would enjoy their videos explaining behind-the-scene details in the context of math, science, and music.

An interesting side note. Anyone who’s been to Hackaday Superconference or one of the monthly Hackaday LA meetups will likely recognized the venue used in many of the OK Go Sandbox videos. Many of them were filmed at the Supplyframe Design Lab in Pasadena. It’s also nice to see AnnMarie Thomas (Hackaday Prize Judge from 2016 and 2017) collaborated with OK Go for the Sandbox project.

While the Science Journal app has provisions for add-on external sensors, carrying them around would reduce its handy always-available appeal. Not that we’re against pairing smartphones with clever accessories to boost their sensing capabilities: we love them! From trying to turn a smartphone into a Tricorder, to an inexpensive microscope, to exploring serious medical diagnosis, our pocket computers can do it all.

[via Engadget]

RF Attack Controls Nearby Smartphones Via “Okay Google” And “Hey Siri”

October 17, 2015 by Brandon Dunson 28 Comments

Most spy movies (at least the ones worth their salt) will include a few scenes that depict nerds in a van listening in on conversations remotely and causing the victims phones to do things like turn themselves or their cameras on. We have been made to believe that it takes an entire van of equipment and one or two MIT level hackers to pull this off. Turns out all it takes is about $2300, some know how, and an unsuspecting target with a set of microphone-equipped headphones attached to their phone.

The French Government’s information security research group ANSSI has been investigating this and published a paper with their findings. Unfortunately that paper is behind a paywall. Wired has a pretty good summation of the findings, which use a transmitter to induce a current in the headphone wires. This in itself isn’t surprising. But they’re able to do it with such accuracy that it can both trigger, and successfully interact with the hands-free features provided by Siri and Google Now.

We think this is a really cool proof-of-concept. It’s mentioned that an attacker could potentially use this to make calls or do other things that cost the victim money. We think it’s more likely to be implemented by resourceful young engineers as a practical joke. Rick Rolling is a poplar go-to. But if you can make the phone “hear” audio, you should also be able to make someone wearing headphones hear ghosts. This has a lot of potential. The first one to make this happen really needs to let us know about it.

CRAYFIS Hijacks Our Cellphones For A Worldwide Cosmic Ray Detector

April 1, 2015 by Sonya Vasquez 20 Comments

Although scientists have known about Ultra-High Energy Cosmic Rays (UHECRs) for years, nobody can pinpoint their origin. When these UHECRs hit the ground, however, they cause a widespread local disturbance called an air shower. This air shower is a wide dispersion of photons, muons, and electrons at sea level. The means of observing this air shower mandates a widespread geographic region for detecting them. One solution would be a very big detector. Physicists [Daniel] and [Michael] discovered an alternative to pricey hardware, though. By leveraging the CMOS sensors in our smartphones, they can borrow some CPU cycles on our phones to create a worldwide detector network.

According to their paper, the CMOS camera in our smartphones is sensitive to the spectrum of radiation induced by muons and photons from these air showers. With an app running on our phones, [Daniel], [Michael], and other scientists can aggregate the data from multiple detections in a similar region to better understand their origins.

If you’re concerned about CRAYFIS taking away from your talk or web-browsing time, fear not; it runs in the background when a power source has been detected, hopefully, when you are asleep. It’s not the first time we see scientists tap into our computing resources, but this is certainly an achievement made possible in only the last few years by the sensor-loaded smartphone that charges on many of our night stands. With over 1.5 billion smartphones active in the world, we’re thrilled to see a team cleverly leveraging a ubiquitous and already-well-distributed resource.

via [NPR]

Easy To Use Automatic QR Code Generator

October 16, 2011 by Mike Nathan 20 Comments

custom_qr_code_generator

Love them or hate them, plenty of people around the world use QR codes on a daily basis. Since he thinks they’re pretty great, Hackaday reader [falldeaf] thought it would be cool to put together an automatic QR code generator to be used on web sites.

Inspired by the custom QR logo embedding work done by our own [Brian Benchoff], his dynamic QR code generator allows you to do the same thing, but with far less work. The code requires that you have PHP and the GD library installed on your server, but other than that his code does the rest.

All you need to do is call up the page and pass along a URL, optional caption text, optional image overlay (to add your logo to the center of the code), as well as an optional hash code for tracking traffic sources. The page spits out a png image that can be used on its own, or embedded in a blog, which is what [falldeaf] plans on using it for.

If QR codes are your thing, be sure to grab a copy of his code, it will certainly be a handy tool to have around.