RFID Record Player

June 6, 2011 by Brian Benchoff 16 Comments

Like most of us at Hack a Day, [Bertrand Fan] has a huge collection of digital music that was all obtained through legal channels. Missing the physical process of choosing and playing an album, [Bertrand] built an RFID record player to get rid of the paradox of choice that arises when thousands of albums are at your fingertips.

The records are repurposed Christmas ornaments with RFID disk tags pasted under the label. These records are read by a RedBee RFID reader and sent to a Popcorn Hour media server, but we’re guessing this could be easily adapted to any HTPC.

The only limitation we see is the fact that the RFID chip is hard coded to individual songs. We think it would be easier to have the RFID chip store an album’s CDDB discid, but feel free to leave a comment and say how you would catalog thousands of albums on RFID tags.

We’re a little tired of skipping though our music collection like a portable CD player from 1990, so we’re pretty impressed that [Bertrand] came up with something that would get us to sit down and listen to our Terabytes of FLAC-encoded music. Check out the video after the jump for a demo of the RFID record player.

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Hidden Messages In Audio

May 26, 2011 by Kevin Dady 24 Comments

[Alex] tiped us off about the evil sounding noises coming from http://www.thedarkknightrises.com/. when you go there your pretty much greeted with a wav file and if you have a quick eye on the status bar its pretty easy to get the direct link to the file and download it. Thats all great, but why would you want to?

Well if you play back the file in a program that supports spectrograms (like audacity) you will find that there is a twitter hash hidden within the audio spectrum, that presents itself as plain text in a pretty well rendered font. Of course this leads you to another part of the site where yet another puzzle awaits you.

While this is all an interesting way to stir up buzz about the upcoming (Batman) movie, we found hiding plain text in an audio file pretty wild, though its been done before or better such as the post we had not too long ago about Ham’s packing QR codes in a similar way.

Generating Pink Noise

May 24, 2011 by Mike Szczys 9 Comments

[Miceuz] just finished his first surface mount electronics project. It’s a pink noise generator that is used for testing audio equipment (scroll down that link for the English version of his writeup).

Pink noise is somewhere in between red noise and white noise. Didn’t realize there were more colors than just white when it comes to noise? The benefit of testing with pink noise is that it the power of the audio signal is stable through each octave of sound – white noise increases in power with each additional octave which can damage the tweeters in a sound system.

The goal in this design was to build a noise generator that fit into an XLR connector. [Miceuz] started with an existing design, and altered it to suit his needs. Much like a condenser microphone, the pink noise generator uses phantom power instead of a standalone power source. For instance, the design he based this on required two 9v batteries. The size, the choice of case, and the absence of a battery all spell WIN for this project.

Class-D Audio Amplifier Makes It From Breadboard To PCB

May 21, 2011 by Mike Szczys 17 Comments

[Ben Laskowski’s] been working on a Class-D audio amplifier for several months. What you see above is the most recent version of the amp. A class-D amplifier uses transistor switching (or in this case MOSFET switching) to generate the pulse-width-modulated signal that drives the speaker. This is different from common amplifiers as it doesn’t generate the kind of heat that traditional amplifiers do, making it much more efficient.

After the break you can hear it demonstrated. It’s operating off of a single-supply laptop brick and we do hear a bit of a hum coming through the system. Still, we’re quite pleased at the power and quality the small board can put out. Take a look at a post from November to get a handle on what went into development. If you still hunger for more details, [Ben’s] shared the bulk of his prototyping materials in the github repository.

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Adding Ethernet Control For A 5.1 Speaker Set

May 16, 2011 by Mike Szczys 12 Comments

[HuB’s] set of 5.1 surround sound speakers was gobbling up a bunch of electricity when in standby as evidenced by the 50 Hz hum coming from the sub-woofer and the burning hot heat sink on the power supply. He wanted to add a way to automatically control the systems and offer the new feature of disconnecting the power from the mains.

The first part was not too hard, although he used a roundabout method of prototyping. He planned to use the IR receiver on the speakers to control them. At the time, [HuB] didn’t have an oscilloscope on hand that he could use to capture the IR protocol so he ended up using Audacity (the open source audio editing suite) to capture signals connected to the input of a sound card. He used this to establish the timing and encoding that he needed for all eight buttons on the original remote control.

Next, he grabbed a board that he built using an ATmega168 and an ENC28J60 Ethernet chip. This allows you to send commands via the Internet which are then translated into the appropriate IR signals to control the speakers and a few other devices in the room. The last piece of the puzzle was to wrap an RF controlled outlet into the project with lets him cut mains power to the speakers when not in use. You can see the video demonstration embedded after the break.

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Touch-based Synthesizer Is A Wiring Nightmare

May 11, 2011 by Mike Szczys 10 Comments

[Jane] wrote in to let us know about the touch-based synthesizer she and her classmates just built. They call it the ToneMatrix Touch, as it was inspired by a flash application called ToneMatrix. We’re familiar with that application as it’s been the inspiration for other physical builds as well.

A resistive touch screen in the surface glass of the device provides the ability to interact by tapping the cells you wish to turn on or off. Below the glass is a grid of LEDs which represent sound bits in the looping synthesizer track. Fifteen shift registers drive the LED matrix, with the entire system controlled by an ATmega644 microcontroller. Although the control scheme is very straight forward, the jumper wires used to connect the matrix to the shift registers make for a ratsnest of wireporn that has been hidden away inside the case. Check out the demonstration video after the break to see what this looks like and sounds like when in use.

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Generating Music With Credit Cards

May 8, 2011 by Mike Nathan 19 Comments

mozarts_credit_card

[Steve] was browsing around at a local electronics surplus store when he spotted an old Tranz 330 point-of-sale terminal that seemed pretty interesting. He took it home and after disassembling it, found that it contained a Z-80 based computer. Because the 330 shares the same processor as other hobbyist-friendly devices such as the TRS-80, he figured it would be quite fun to hack.

While the Z-80 processor is pretty common, [Steve] still had to figure out how it was interfaced in this particular device. After spending some time reverse engineering the terminal, he had free reign to run any program he desired. After thinking for a bit, he decided it would be cool to use the terminal to generate music based on whatever card was swiped through the reader – he calls his creation “Mozart’s Credit Card”.

He found that just playing sounds based on the raw contents of the mag strips didn’t produce anything coherent, so he wrote a small application for the terminal based on the Melisma Stochastic Melody Generator. Music is generated somewhat randomly using various card characteristics, as you can see in the video below.

We think it’s pretty cool, but [Steve] says he’s always open to suggestions, so let us know what you think in the comments.

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