Escape Cable Hell with an Audio I/O Multiplexer

If you ever find yourself swapping between a mix of audio inputs and outputs and get tired of plugging cables all the time, check out [winslomb]’s audio multiplexer with integrated amplifier. The device can take any one of four audio inputs, pass the signal through an amplifier, and send it to any one of four outputs.

The audio amplifier has a volume control, and the inputs and outputs can be selected via button presses. An Arduino Pro Mini takes care of switching the relays based on the button presses. On the input side, you can plug in devices like a phone, TV, digital audio player or a computer. The output can be fed to speakers, headsets or earphones.

At the center of the build lies a TI TPA152 75-mW stereo audio power amplifier. This audio op-amp is designed to drive 32 ohm loads, so performance might suffer when connecting it to lower impedance devices, but it seems to work fine for headphones and small computer speakers. The dual-gang potentiometer controls the volume, and the chip has a useful de-pop feature. The circuit is pretty much a copy of the reference shown in the data sheet. Switching between inputs or outputs is handled by a bank of TLP172A solid state relays with MOSFET outputs, and it’s all tied together with a micro-controller, allowing for WiFi or BLE functionality to be added on later.

[winslomb] laid out the design using Eagle and he made a couple of footprint mistakes for the large capacitors and the opto-relays. (As he says, always double-check part footprints!) In the end, he solder-bridged them on to the board, but they should probably be fixed for the next revision.

[winslomb] built the switch as his capstone project while on his way to getting a Masters in EE, and although the device did function as required, there is still room for improvement. The GitHub repository contains all the hardware and software sources. Check out the video below where he walks through a demo of the device in action. If you are looking for something simpler, here is a two input – one output audio switcher with USB control and on the other end of the spectrum, here’s an audio switch that connects to the Internet.

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Even if I could take off, I could never get past the tractor beam!

Finally our childhood dreams of a working tractor beam are coming to fruition! It’s called acoustic levitation and it actually uses highly concentrated sound waves to float small objects by essentially creating an acoustic force field.

The concept is nothing new, in fact we first covered it back in 2014 — but since then they’ve made leaps and bounds in their research. Back then they could just levitate dust. Now we’re moving onto small objects, like googly-eyes! It’s perceivable that with powerful enough speakers, larger objects will soon be harnessed…

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Random Parcel Launches Steganographic Compulsion

A mysterious CD arrives in the mail with a weird handwritten code on it. What should you do? Put it in the computer and play the thing, of course!

Some might be screaming at their screens right now… this is how modern horror films start and before you know it the undead are lurking behind you waiting to strike. Seasonal thrills aside, this is turning into an involved community effort to solve the puzzle. [Johny] published the video and posted a thread on reddit.

We ran a similar augmented reality game to launch the 2014 Hackaday Prize solved by a dedicated group of hackers. It’s really hard to design puzzles that won’t be immediately solved but can eventually be solved with technology and a few mental leaps. When we come across one of these extremely clever puzzles, we take note.

This has all the hallmarks of a good time. The audio spectrogram shows hidden data embedded in the file — a technique known as steganography. There are some real contortions to make meaning from this. When you’re looking for a solution any little hit of a pattern feels like you’ve found something. But searching for the decrypted string yields a YouTube video with the same name; we wonder if they’ve tried to recover steganographic data from that source?

[Johny] mentions that this parcel was unsolicited and that people have suggested it’s a threat or something non-sensical in its entirety. We’re hoping it’s a publicity stunt and we’re all disappointed in the end, because solving the thing is the best part and publicity wouldn’t work if there was no solution.

The bright minds of the Hackaday community should be the ones who actually solve this. So get to work and let us know what you figure out!

Electronics for Aliens

We are surrounded by displays with “millions” of colors and hundreds of pixels per inch. With super “high fidelity” sound producing what we perceive to be realistic replicas of the real world.

Of course this is not the case, we rarely stop and think how our electronic systems have been crafted around the limitations of human perception. So to explore this issue, in this article we ask the question: “What might an alien think of human technology?”. We will assume a lifeform which senses the world around it much as we do. But has massively improved sensing abilities. In light of these abilities we will dub it the Oculako.

Let’s begin with the now mostly defunct CRT display and see what our hypothetical alien thinks of it. The video below shows a TV screen shot at 10,000 frames per second.

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The Ubiquitous Atari Punk Console

The Atari Punk Console (APC) is a dual 555 (or single 556) based synth. Designed by the famous (and somewhat infamous) Forrest Mims in 1980 and originally simply named “Sound Synthesizer”, the circuit gained it’s more recent popularity when re-dubbed the “Atari Punk Console” by Kaustic Machines. The circuit however doesn’t bear much relation to the Atari 2600 which didn’t contain a 555 timer chip. However we assume the 2600 produced a similarly glitchy square wave audio output.

a2The circuits operation is easy to grasp and uses only 9 components. This ease of design and construction has allowed builders to focus more on the aesthetics of its construction, hacking it into interesting, and often unlikely enclosures and systems. One such hack is the “Atari Punk Bucket” (shown here) where the APC along with a simple amp was hacked into an old rusted bucket. The APC was built up on strip-board along with a simple amp and reclaimed speakers. [Farmer glitch] has used this as a prop in live sets and it both looks and sounds awesome. Continue reading “The Ubiquitous Atari Punk Console”

Make a Microphone Out of a Hard Drive

[Rulof Maker] has a penchant for making nifty projects out of old electronics. The one that has caught our eye is  a microphone made from parts of an old hard drive. The drive’s arm and magnet were set aside while  the aluminum base was diagonally cut into two pieces.  One piece was later used to reassemble the hard drive’s magnet and arm onto a wooden platform.

v2_micThe drive’s arm and voice coil actuator are the key parts of this project. It was modified with a metal extension so that a paper cone cut from an audio speaker could be attached, an idea used in microphone projects we’ve previously featured. Copper wire scavenged from the speaker was then soldered to voice coil on the arm as well as an audio jack. In the first version of the Hard Drive Microphone, the arm is held upright with a pair of springs and vibrates when the cone catches sound.

While the microphone worked, [Rulof] saw room for improvement. In the second version, he replaced the mechanical springs with magnets to keep the arm aloft. One pair was glued to the sides of the base, while another pair recovered from an old optical drive was affixed to the arm. He fabricated a larger paper cone and added a pop filter made out of pantyhose for good measure. The higher sound quality is definitely noticeable. If you are interested in more of [Rulof’s] projects, check out his YouTube channel.

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Update: Battlezone on Vector Display Step-by-Step

When we ran the story of Battlezone played on tube displays earlier this week there were immediately questions about recreating the hack. At the time the software wasn’t available, and there is also a bit of hardware hacking necessary to get the audio working. You asked and [Eric] from Tubetime delivered. He’s posted a pair of articles that show how to get an STM32F4 Discovery board to play the classic game, along with instructions to build the firmware.

The hardware hack in this case is untangling the pinout used on the discovery board. It seems that one of the lines needed to get sound working for this hack is tied to one of the two DACs. If you read the original coverage you’ll remember that both of the DACs are used to drive X and Y on the vector display. The image above shows a cut trace on the bottom of the board. You’ll then need to route that signal to an alternate pin by soldering a jumper wire from the chip to a resistor on the board.

This (as well as one other alteration that bridges two of the chip pins) is a great example of work you should be unafraid to do on your own dev boards. We’ve had to do it with the Launchpad boards to get at the functionality we needed. We’d like to hear your own epic stories of abusing dev boards to do your bidding. Let us know in the comments.