Name That Unknown RF Signal With A Little FFT Magic

February 11, 2020 by Dan Maloney 27 Comments

Time was once that the amateur radio bands were an aurally predictable place. Spinning the dial up and down the bands, one heard familiar sounds – the staccato of Morse, the [Donald Duck] of sideband voice transmissions, and the occasional flute-like warble of radioteletype signals. Now, the ham bands are full of exotic signals encoding all manner of digital signals, each one with a unique sound and unique demodulation needs. What’s a ham to do?

Help is on the way. [José Carlos Rueda] has made progress toward automatically classifying unknown signals by modifying a Shazam-like app. Shazam is a popular smartphone app that listens to a few seconds of a song, creates an audio fingerprint of it, and searches a massive database of songs for a match. [Rueda] used a homebrew version of the app to search a SQL-lite database of audio fingerprints populated not with a playlist of popular music, but with samples from every known signal type in the Signal Identification Wiki. The database contains hashes for an FFT of each sample, which can be easily searched. With a five to ten second sample of a signal, captured either live over a microphone or from a recording, he is able to identify the signal automatically.

Whether it be the weird, dissonant wail of PSK-31 or the angry buzzing of PACTOR, the goings-on across the bands no longer have to remain a mystery. We really like the idea here, and wonder if it can be expanded upon to visually decode signals based on their waterfall signatures using TensorFlow. There are some waterfall examples in [Danie Conradie]’s excellent article on RF modulation that could get you started.

[via RTL-SDR.com]

Airport Split-Flap Letters Carry On As Spotify Display

February 11, 2020 by Kristina Panos 25 Comments

Today’s tale of being in the right place at the right time comes from [fabe1999], who was doing an intern gig at the airport when the controller on their split-flap display bought a one-way ticket going south. They were just going to throw away thousands of these letters and replace them with monitors, but the intern intervened.

[fabe1999] grabbed an armload, took them home, and set about making them flap again, one letter at a time. An ATtiny worked okay, but it wasn’t really fast enough to flip them at their full clacking potential, so [fabe1999] switched to an ESP8266. So now there is one ESP for each of the 20 characters, and another that runs a web server where text can be directly entered for immediate display.

Each letter uses two sensors to flap to the right letter. The first one acts as a start sensor, detecting the blackness of a blank character. Another sensor counts the letters and makes the ESP stop the motor on the right one. So far, [fabe1999] hasn’t figured out how to recognize when a blank character can stay blank, so they flap all the way around back to blank for now. It certainly adds to the rich, flappy sound, but that can’t be good for the long-term life of the letters. Your flight is now departing for Post Break Island, where the letters are spending part of their retirement showing song titles from Spotify.

No chance of split flaps falling into your lap? Here’s a tip: you can fab your own flip.

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A French Press You Can Take Out Camping

February 10, 2020 by Lewin Day 41 Comments

There’s many a hacker that considers coffee a necessary fuel, without which, little work can be achieved. This applies whether in the office or traipsing around in the great outdoors. For the latter situation, [Poehls05] developed a robust French press that’s well suited to field use.

Typically, a French press consists of a plunger assembly which moves within a glass vessel. This is fragile and unwieldy for throwing in a backpack. Instead, in this design, the plunger assembly is harvested from an existing press and repurposed to fit within a sturdy Nalgene water bottle, designed specifically for overlanding.

The modifications involve cutting the existing press plate into three slices, and reassembling with hinges so it may fold. The plunger rod is then modified to make it possible to tilt the press plate relative to the rod. These modifications allow the plunger to be slid into the narrower neck of the Nalgene water bottle, and also enable the plunger rod to work with the original screw-down lid. In this configuration, the bottle is no longer water tight, but can be converted to normal use by swapping a regular lid back on top.

With the changes in place, the plastic bottle can easily be used in the same manner as a regular French press. Simply fill with hot water, allow the grounds to steep, and then press and pour. It’s a great way to make high-quality coffee in the wilderness, and one that may prove popular with hackers who don’t wish to give up the finer things when out and about. We’ve also featured tricks to make the most of hotel coffee, too.

Hacking Multiplication: Binary Multiply On Paper

February 7, 2020 by Al Williams 12 Comments

We’ve often noted that whether had ancient man known binary, we could all count to 1023 on our fingers. We thought about that while watching [Numberphile’s] latest video about “Russian” multiplication (see below). Apparently, the method dates back quite a way, sometimes known as Ethiopian or peasant multiplication. Even the ancient Egyptians did a form of it.

If you’ve ever written long multiplication code for a microcontroller, you can probably tell how this works. Each halving of the number amounts to a right shift. Each doubling is a left shift. Throwing out the even numbers means you only take the values when the least-significant bit is zero. Booth’s algorithm is more efficient, but the “Russian” method is simple to do on paper.

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Custom Laser Tag Rifle Packs A Sonic Punch

February 6, 2020 by Lewin Day 33 Comments

Laser tag is rarely (if ever) referred to as “The Sport of Kings”, but is a fun pastime nonetheless. While some are content to play with off-the-shelf toys, others prefer to make their own gear to suit their needs. [Heine Nielsen] is just one such builder, creating a fully-featured laser rifle loaded with features.

As far as hardware goes, [Heine]’s laser rifle is packed to the gills. There are two ESP32s running the show, along with a meaty 6S lithium battery to provide plenty of juice for long combat sessions. A 40W audio amp is hooked up to a speaker mounted in a faux-grenade launcher, aping the design of the M203 – and is able to deliver ear-splitting sound for that realistic touch.

Knowing the popularity of modern FPS games, [Heine] cribbed a lot from titles like PUBG and CS:GO. Grabbing sound effects from various weapons was just one step, with the ultimate goal being to replicate advanced game modes from these games. To help keep the player aware of the game state, there’s even a HUD on the gun, thanks to a 2.8″ TFT screen tucked into the scope.

It’s a serious build for playing serious laser tag, and we’d love to head out to the field for a match with gear like this. We’ve seen other hyper-realistic builds before too, like this one that uses actual blanks. Video after the break.

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Array Of Useless Machines Is Useless

February 5, 2020 by Richard Baguley 38 Comments

What’s the collective noun for a group of useless machines? A passel of useless machines? A failure? A waste? A 404? Whatever you want to call it, [Martin Raynsford] has produced one here with this collection of 24 useless machines arranged into a 5 by 6 array. He produced it for an event at a hackerspace to amuse visitors, and it certainly seems to do the job in the video after the break.

[Martin] built the case by modifying the design of his Useless Machine kit, stretching out the case to hold multiple mechanisms. The original plan was to use a 6 by 6 matrix, but that wouldn’t fit into the laser cutter, so it ended up with 24 mechanisms in a 5 by 6 array. All of those are driven by 2 AAA batteries, and the mechanisms are efficient enough that it survived a full day of button flipping before it began to run out of juice.

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Hoverboard Grows Up, Becomes Magnetic Drill Press

February 4, 2020 by Kristina Panos 11 Comments

If you need to drill metal in tight places, the magnetic drill press, or mag drill is your BFF. The idea here is that a drill press with an electromagnetic base can go anywhere, and even drill horizontally if need be. If you don’t need to use one often, but want one anyway, why not build one out of e-waste?

[DIY KING 00] built this mag drill starting with the motor from a hoverboard. While these three-phase brushless motors have a lot of torque to offer reuse projects like this, they’re not designed to be particularly fast.

He was able to make it about three times faster by cutting the windings apart and reconnecting them in parallel instead of series. He designed a simple PCB to neatly tie all the connections back together and added an electronic speed control (ESC) from an R/C car.

Reluctant to give up the crown, he made his own three-coil electromagnetic base, using a drill to wind magnet wire around temporary chuck-able cores. The coils are then potted in epoxy to keep out dust and drilling debris. Everything runs from two large LiPo batteries, and he can get about 15 minutes of high-torque drilling done before they’re dead. Can you feel the electromagnet pulling you past the break to check out the build and demo video?

Depending on what you’re doing, you might get away with a magnetic vise instead.

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