Here’s How Those Battery-Free Flashing Phone Stickers Worked

The late 90s and early 2000s were a breakout time for mobile phones, with cheap GSM handsets ushering in the era in which pretty much everybody had a phone. Back then, a popular way to customize one’s phone was to install a sticker that would flash when the phone rang. These required no batteries or any other connection to the phone, and [Big Clive] has dived in to explain how they worked. 

The simple schematic of the flashing sticker circuit. The flashing was generated by the pulses of RF energy from the smartphone.

It’s an old-fashioned teardown that requires a bit of cutting to get inside the sticker itself. A typical example had three LEDs in series for a total voltage drop of around 7V, hooked up to two diodes and a PCB trace antenna. A later evolution used raw unpackaged components bonded to the PCB. Future versions went down to a single diode, using the LEDs to serve as the second. The basic theory was that the PCB traces would pick up RF transmitted by the phone when a call was coming in, lighting the LEDs.

In the 2G era, the freuqencies used were on the order of 300 MHz to 1.9GHz. A combination of the change in frequencies used by modern phone technology and the lower transmit powers used by handsets means that the stickers don’t work properly with modern phones according to [Big Clive].

Incidentally, you might like to consider running your own old-school cellphone network. Video after the break.

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A Rotary Phone As A Computer Peripheral

It’s an age-old conundrum for anyone working with retro hardware: preserve its original condition or not? The answer depends so often on a complex mix of how rare, obsolete or unusable the device is in its original form , and what the intended use for the device will be. For [Typhon Mind] who needed a novelty method of recording best wishes at a wedding through an old dial phone there was no need for it to be entirely original, so the solution was to turn it into a USB device for a host computer.

Out went the original circuitry, and in came a USB hub, a USB audio interface, and an Arduino. The original earpiece would suffice, but the microphone was replaced with a more modern one. The Arduino will register the cradle switch, and also power a set of LED addressable lights under the unit.

The result is a phone that retains all its looks, but has a new life as a PC peripheral. We’d venture to suggest that also using the Arduino to read the dial and produce DTMF tones might make it a valid peripheral for a VOIP application and complete the transformation, but that’s something that could be done at a later date. Maybe it could even be given a GSM makeover.

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Hackaday Links: October 31, 2021

Global supply chain issues are beginning to hit closer to home for the hacker community, as Raspberry Pi has announced their first-ever price increase on their flagship Pi 4. The move essentially undoes the price drop on the 2GB version of the Pi 4 that was announced in February, and sets the price back up from $35 to $45. Also rolled back is the discontinuation of the 1GB version, which will now be available at the $35 price point. The announcements come from Eben Upton himself, who insists the price increase is only temporary. We applaud his optimism, but take it with a grain of salt since he also said that 2021 production across the board will stay at the seven million-unit level, which is what they produced in 2020. That seems to speak to deeper issues within the supply chain, but more immediately, it’s likely that the supply of Pi products will be pinched enough that you’ll end up paying above sticker price just to get the boards you need. Hope everyone is stocked up.

On the topic of supply chain issues and their threat to Christmas gift-giving, here’s one product we hope is stranded in a container off Long Beach or better still, bobbing along in the Strait of Juan De Fuca: a toddler’s toy telephone that actually makes and receives calls. Anyone born in the last 60 years probably had one of the Fisher-Price Chatter telephone, a toy that in its original form looked like a desk telephone on wheels that was dragged behind the child, popping along and providing endless hours of clicky amusement as kids twisted the dial and lifted the receiver. Come to think of it, the Chatter telephone may be as close to a dial phone as anyone born since 1990 may have come. Anyway, some genius stuck a Bluetooth module into the classic phone to let it hook up to an app on an actual phone, allowing kids (or more likely their nostalgia-soaked parents) to make and receive calls. It’s actually priced at a reasonable $60, so there might be some hacking potential here.

Also tangential to supply chains, we stumbled across a video guide to buying steel that might interest readers. Anyone who has seen the displays of steel and other metals at the usual big-box retailers might wonder what the fuss is, but buying steel that way or ordering online is a great way to bust a project’s budget. Fabricator and artist Doug Boyd insists that finding a local steel supplier is the best bang for your buck, and has a bunch of helpful tips for not sounding like a casual when you’re ordering. It’s all good advice, and would have helped us from looking foolish a time or two at the metal yard; just knowing that pipe is measured by inside diameter while tubing is measured by outside dimensions is worth the price of admission alone.

With all the money you save on steel and by not buying Raspberry Pis, perhaps you’ll have a couple of hundred thousand Euros lying around to bid on this authentic 1957 Sputnik I satellite. The full-scale model of Earth’s first artificial satellite — manhole covers excluded — was a non-flown test article, but externally faithful to the flown hardware that kicked off the first Space Race. The prospectus says that it has a transmitter and a “modern power supply”; it’s not clear if the transmitter was originally part of the test article or added later. The opening bid is €85,000 and is expected to climb considerably.

And finally, there’s something fascinating about “spy radios,” especially those from the Cold War era and before, when being caught with one in your possession was probably going to turn out to be a very bad day. One such radio is the Radio Orange “Acorn” receiver, which is in the collection of the Crypto Museum. The radio was used by the Dutch government to transmit news and information into the occupied Netherlands from their exile in London. Built to pass for a jewelry box, the case for the radio was made from an old cigar box and is a marvel of 1940s miniaturization. The radio used three acorn-style vacuum tubes and was powered by mains current; another version of the Radio Orange receiver was powered by a bike dynamo or even a water-powered turbine, which could be run from a tap or garden hose. The video below shows the water-powered version in action, but the racket it made must have been problematic for its users, especially given the stakes.

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A Tidy Clamshell Keyboard For The Pinephone

Something a lot of people don’t realise about modern smartphones is that many of them have fully-featured USB interfaces. Perhaps the best of all is the Pinephone, which is a fully open-source smartphone that gives end users total control over their phone experience. [silver] has such a phone, and set about building himself a neat keyboard setup for the platform.

The build is based around an RCA RKT773P tablet keyboard case, which uses USB to interface with a tablet via pogo pins. [silver] modified this by soldering on a USB cable to the pins, paired with a USB-C host adapter on the Pinephone. Paired with a few 3D printed parts to hold everything in place, it almost turns the assembly into a cute little Pinephone laptop.

It’s a neat build that would likely save a lot of frustration when hacking away at a terminal window on the Pinephone. Parts are available on Thingiverse for those interested in replicating the hack. Those eager to dive into the Pinephone platform may relish the new Pro model that has just dropped, too. Video after the break.

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Build Yourself A Nifty Cable Smartphone Mount

Smartphones have supplanted cameras in day to day use for the vast majority of purposes. However, unlike cameras, they don’t come with tripod mounts or any real good way of holding them in a set position. [Mrballeng] has built an excellent mount, however, that uses cable to hold a smartphone in all manner of positions, for photography or other purposes.

The mount relies on vinyl-coated steel cable. Upon this cable are slotted four blocks that are 3D printed out of resin. The blocks are also fitted with strong magnets. This allows them to be positioned along the vinyl cable while sticking themselves in place thanks to the magnetic attraction to the steel core. The blocks can also be used to attach the cable to magnetic objects like drywall screws or light fittings.

Using the mount is simple. The cable is wrapped around the phone and the blocks cinched up to hold it in place. Then, the magnets in the blocks can be used to hold the phone to walls or other surfaces.

It’s a tidy build, and one we can imagine using regularly if we had one. Of course, there’s no reason you couldn’t produce the parts on a more common filament-based printer, either. We’ve seen some other great smartphone photography hacks too, like this mod that lets you use your phone as a microscope for under $10. Video after the break.

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Old Phone Becomes MIDI Controller

MIDI controllers come in all shapes and sizes. Commercial products based on keyboards or matrixes of buttons are popular, but there’s nothing stopping you from whipping up your own creations out of whatever strikes your fancy. [Kevin] has done just that, turning an old telephone into a working MIDI device.

The phone in question is a Doro X20 wired landline phone. Being surplus to [Kevin’s] requirements left it ripe for the hacking. A Raspberry Pi Pico was wired in to the phone’s keypad, slimmed down with a hacksaw in order to allow it to neatly fit inside the original enclosure. Then it was a simple matter of whipping up some code to read the buttons and output MIDI data via the Pico’s serial output.

Later, [Kevin] brought the design into the modern world, setting it up to talk USB MIDI using the Pico’s onboard USB hardware. This makes using it with a computer a cinch, and lets [Kevin] control a DAW using the handset controller.

It’s a fun build, and one that shows how you can easily build your own MIDI hardware using nothing but a soldering iron, some buttons, and a modern microcontroller. From there, the sky really is the limit. Whether you like big knobs, easy playing, or have your own personal tastes, you can build what you like to suit your own style. When you do, drop us a line! Video after the break.

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The 70s Are Calling To Shed Some Light

Remember when phones didn’t all look the same? We had a good thing going in the early cell phone days, which seemed like a brief holdover from the Western Electric (et. al) era where you could get a phone that suited your inner minimalist or princess, and choose the color to boot.

[Dubchinsky] found a beautiful phone from this bygone era and saved it from one of two likely fates — the landfill, or else a life languishing as a piece of vintage technology that’s just sitting around for looks. Instead, this phone found a second calling as a lovely desk lamp with secret goose neck flexibility. The lamp itself is an inexpensive LED module from ebay that’s wired up to mains power through a push button switch in the phone’s base.

We absolutely love that [Dubchinsky] wrapped the curly cord around the goose neck, but were a bit disappointed that he didn’t use the hook switch to turn the lamp on and off. In the comments, he says that the plastic felt like it was too brittle to stand up to repeated actuation of such a heavy switch. That’s understandable. [Dubchinsky] also thought about using the rotary dial as a dimmer, and we think that’s a bright idea.

Between the guide, the pictures, and the build process video after the break, this is pretty much a complete how-to. We think that is commendable given that [Dubchinsky] is selling these lamps on etsy.

Do ya miss spinning the rotary dial and long for somewhat simpler days? Hook your finger into this rotary cell phone.

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