Digital to Analog to Digital to Analog to Digital Conversion

[Andy] had the idea of turning a mixing desk into a MIDI controller. At first glance, this idea seems extremely practical – mixers are a great way to get a lot of dials and faders in a cheap, compact, and robust enclosure. Exactly how you turn a mixer into a MIDI device is what’s important. This build might not be the most efficient, but it does have the best name ever: digital to analog to digital to analog to digital conversion.

The process starts by generating a sine wave on an Arduino with some direct digital synthesis. A 480 Hz square wave is generated on an ATTiny85. Both of these signals are then fed into a 74LS08 AND gate. According to the schematic [Andy] posted, these signals are going into two different gates, with the other input of the gate pulled high. The output of the gate is then sent through a pair of resistors and combined to the ‘audio out’ signal. [Andy] says this is ‘spine-crawling’ for people who do this professionally. If anyone knows what this part of the circuit actually does, please leave a note in the comments.

The signal from the AND gates is then fed into the mixer and sent out to the analog input of another Arduino. This Arduino converts the audio coming out of the mixer to frequencies using a Fast Hartley Transform. With a binary representation of what’s happening inside the mixer, [Andy] has something that can be converted into MIDI.

[Andy] put up a demo of this circuit working. He’s connected the MIDI out to Abelton and can modify MIDI parameters using an audio mixer. Video of that below if you’re still trying to wrap your head around this one.

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The Four Thousand Dollar MP3 Player

[Pat]’s friend got a Pono for Christmas, a digital audio player that prides itself on having the highest fidelity of any music player. It’s a digital audio device designed in hand with [Neil Young], a device that had a six million dollar Kickstarter, and is probably the highest-spec audio device that will be released for the foreseeable future.

The Pono is an interesting device. Where CDs have 16-bit, 44.1 kHz audio, the Pono can play modern lossless formats – up to 24-bit, 192 kHz audio. There will undoubtedly be audiophiles arguing over the merits of higher sampling rates and more bits, but there is one way to make all those arguments moot: building an MP3 player out of an oscilloscope.

Digital audio players are limited by the consumer market; there’s no economical way to put gigasamples per second into a device that will ultimately sell for a few thousand dollars. Oscilloscopes are not built for the consumer market, though, and the ADCs and DACs in a medium-range scope will always be above what a simple audio player can manage.

[Pat] figured the Tektronicx MDO3000 series scope sitting on his bench would be a great way to capture and play music and extremely high bit rates. He recorded a song to memory at a ‘lazy’ 1 Megasample per second through analog channel one. From there, a press of the button made this sample ready for playback (into a cheap, battery-powered speaker, of course).

Of course this entire experiment means nothing. the FLAC format can only handle a sampling rate of up to 655 kilosamples per second. While digital audio formats could theoretically record up to 2.5 Gigasamples per second, the question of ‘why’ would inevitably enter into the minds of audio engineers and anyone with an ounce of sense. Short of recording music from the master tapes or another analog source directly into an oscilloscope, there’s no way to obtain music at this high of a bit rate. It’s just a dumb demonstration, but it is the most expensive MP3 player you can buy.

8-Bit Chip Rocks 16-Bit 44.1kHz Tunes

There’s a special place in our hearts for chip tunes generated with your favorite microcontroller. But why stop there? Full-featured audio is a great challenge and it’s not often we see examples of this caliber. It puts out CD-quality audio using not much more than a microcontroller.

How do you get 16-bit audio out of an 8-bit microcontroller. We’ll give you a hint: two pins are used. Not helping? Here it comes: two 8-bit DACs PWM outputs are used on this chip, the ATmega1284. One is used for the lower eight bits, the other handles the upper. The two are combined using carefully calculated precision resistor values and the results are beyond what you imagine. This is produced at a bitrate of 44077.135, slightly off from the 44100Hz standard but we challenge you audiophiles to tell the difference. The wave files are served from an SD card read by the chip using the Petit-FatFs library.

There are so many great things about this project. First off, following [Wancheng Zhou’s] example will let anyone with even basic microcontroller skills build a digital audio player for an [Andrew Jackson] and a couple of [Washingtons]. Secondly, those with a medium uC skill level will want to take the idea and implement/debug it for themselves. Bringing it home, [Wancheng] shows how to gauge the quality of the audio output using FFT.

If you didn’t figure it out by the time of year, this is yet another example of a Cornell ECE 4760 final project. Shout out to [Bruce Land] for inspiring awesome projects and requiring extensive documentation of the projects which itself promotes deeper understand all around.

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World’s First Smart Snowboard Changes Music According To Your Actions

Ever wanted a soundtrack to your life? For a couple of minutes at a time, Signal Snowboards creates that experience with a smart snowboard that varies your music depending on the tricks you perform on your way down the mountain.

The sign on the door says “School For Gifted Hackers”. Inside [Matt Davis] helped interface audio with an accelerometer – something he regularly does with all manner of hacked devices. At first the prototype was an iPhone mimicking the motions of a snowboarder the way fighter pilots describe dogfights with their hands. The audio engine that pulls those mostions to sound is open source and anyone is welcome to do their own tuning.

Once the audio was figured out the boys took it back to their shop and embedded the sensors into a new snowboard. The board is equipped with GPS, an accelerometer, a few rows of LEDs and a bluetooth board to connect to the phone app. It’s all powered by an on-board LiPo battery and a barrel jack out the side to charge it. Channels were cut by hand with a router then electronics sealed in place with epoxy. Not wanting to “just strap some Christmas lights onto a snowboard” the lighting is also connected to the sensors and is programmable.

See the video below of them making the board and taking it out for a test run on Bear Mountain.

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$15 Car Stereo Bluetooth Upgrade

We’ve seen all sorts of ways to implement Bluetooth connectivity on your car stereo, but [Tony’s] hack may be the cheapest and easiest way yet. The above-featured Bluetooth receiver is a measly $15 over at Amazon (actually $7.50 today—it’s Cyber Monday after all) and couldn’t be any more hacker-friendly. It features a headphone jack for plugging into your car’s AUX port and is powered via USB.

[Tony] didn’t want the receiver clunking around in the console, though, so he cracked it open and went about integrating it directly by soldering the appropriate USB pins to 5V and GND on the stereo. There was just one catch: the stereo had no AUX input. [Tony] needed to rig his own, so he hijacked the CD player’s left and right audio channels (read about it in his other post), which he then soldered to the audio output of the Bluetooth device. After shoving all the bits back into the dashboard, [Tony] just needed to fool his stereo into thinking a CD was playing, so he burned a disc with 10 hours of silence to spin while the tunes play wirelessly. Nice!

Speaker Cabinet Boom Box Build

When you get that itch to build something, it’s difficult to stop unless you achieve a feeling of accomplishment. And that’s how it was with [Rohit’s] boombox build.

He started out with a failing stereo. He figured he could build a replacement himself that played digital media but his attempts at mating microcontrollers and SD cards was thwarted. His backup plan was to hit DX for a cheap player and he was not disappointed. The faceplate he found has slots for USB and SD card, 7-segment displays for feedback, and both buttons and a remote for control. But this little player is meant to feed an amplifier. Why buy one when you can build one?

[Rohit] chose ST Micro’s little AMP called the TDA2030 in a Pentawatt package (this name for a zig-zag in-line package is new to us). We couldn’t find stocked chips from the usual suspects but there are distributors with singles in the $3.50-5 range. [Rohit] tried running it without a heat sink and it gets hot fast! If anyone has opinions on this choice of chip (or alternatives) we’d love to hear them.

But we digress. With an amp taken care of he moved onto sourcing speakers. A bit of repair work on an upright set got them working again. The bulky speaker box has more than enough room for the amp and front-end, both of which are pretty tiny. The result is a standalone music player that he can be proud of having hacked it together himself.

‘Nutclough’ Circuit Board Design is Stylishly Amplified

Though there is nothing wrong with the raw functionality of a plain rectangular PCB, boards that work an edge of aesthetic flare into their layout leave a lasting impression on those who see them. This is the philosophy of circuit artist [Saar Drimer] of Boldport, and the reason why he was commissioned by Calrec Audio to create the look for their anniversary edition amplifier kit. We’ve seen project’s by [Saar] before and this ‘Nutclough18’ amplifier is another great example of his artistic handy work.

nutclough2For the special occasion of their 50th anniversary, Calrec Audio contacted [Saar] requesting he create something a bit more enticing than their standard rectangular design from previous years. With their schematic as a starting point, [Saar] used cardboard to mock-up a few of his ideas in order to get a feel for the placement of the components. Several renditions later, [Saar] decided to implement the exact proportions of the company’s iconic Apollo desk into the heart of the design as an added nod back to the company itself. In the negative space between the lines of the Apollo desk there is a small perforated piece depicting the mill where the Calrec offices are located. The image of the mill makes use of different combinations of copper, silk and solder mask either absent or present to create shading and depth as the light passes through the board. This small piece that would have otherwise been removed as scrap can be snapped off from the body of the PCB and used as a commemorative keychain.

With the battery and speaker mounted behind the completed circuit board, [Saar’s] design succeeds in being a unique memento with a stylish appeal. There is a complete case study with detailed documentation on the Nutclough from cardboard to product on the Boldport website. Here you can also see some other examples of their gorgeous circuit art, or checkout their opensource software to help in designing your own alternative PCBs.