Steering Sound with Phased Array

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[Edward] and [Tom] managed to build an actual phased array speaker system capable of steering sound around a room. Powered by an Atmega 644, this impressive final project uses 12 independently controllable speakers that each have a variable delay. By adjusting the delay at precise intervals, the angle of maximum intensity of the output wave can be shifted, there by “steering” the sound.

Phased arrays are usually associated with EM applications, such as radar. But the same principles can be applied to sound waveforms. The math is a little scary, but we’ll walk you through only what you need to know in case you’re ever in need to steer sound with a speaker and a servo phased array sound system.

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Simon Says learn how to program ARM chips

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This breadboard version of a Simon Says game is a great way to try your skills on a new microcontroller platform. The eight-pin chip seen in the center of the board is an LPC810 microcontroller which [Hartmut Wendt] is just getting started with. It’s a rare example of a low-pin count DIP package for an ARM device (Cortext M0). The breadboard friendly footprint makes it easy to work with, but you could pull off the same build with a dev board like one of the STM discovery offerings or the Stellaris Launchpad boards.

Why is this a good way to learn? It involves input, output, and generating waveforms which we’d assume means timers (we didn’t dig through the source code which is available form the page linked above). Each colored button has a matching LED which blinks out the pattern which you must replicate to keep the game going; you know how Simon Says works, right?. At the same time a different pitch is played by the speaker on the right.

Another good exercise would be to take [Hartmut's] code and port it for a different chip, be it ARM or otherwise.

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Bubble wrap cure for Nexus 7 speaker distortion

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[Home Brand Cola] is quite happy with his Nexus 7 with the exception of the built-in speaker. It produces fairly good audio quality until he reaches about 50% volume level. Anything above that produces distortion. He figured out how to fix it using a small piece of bubble wrap.

The eureka moment came when he was using his Nexus 7 and discovered he could fix the distortion by gripping the top and bottom parts of the case strongly between his finger and thumb. This led him to realize that the speaker unit is a bit loose and the unwanted noise is produced when it vibrates against the case. The video after the break shows the fix, which places a strip of bubble wrap (looks to be about 1″ by 3″) on top of that speaker unit. When the case is snapped back together the packing material helps hold everything in place and now he can use his tablet at full volume without any problems. One of the comments on the Reddit thread asks about heat problems with the addition of this plastic. He’s been using it for a few weeks and so far no issues there.

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How to make your own piezoelectric speaker

Piezoelectric speakers are found all around you, from musical greeting cards to the tweeters in your car stereo setup. Making your own piezo speakers is actually very easy, as [Steven] shows us after replacing the speaker in a clock radio.

Piezo speakers require a small crystal with piezoelectric properties, so this build is the perfect followup to [Steven]‘s tutorial for making Rochelle salt crystals. After attaching two strips of aluminum foil to his Rochelle salt crystal, [Steven] took the wires that previously went to the clock radio speaker, connected them to the crystal, and turned on the radio. When attached to a tin can, the newly created piezo speaker created a little bit of sound, but the results weren’t very impressive.

To boost the sound output of his homemade speaker, [Steven] needed to increase the voltage across his piezo speaker. At first he tried a doorbell transformer with somewhat better results, but much more sound was produced when he used a transformer taken from a microwave oven.

After experimenting with his microwave transformer and Rochelle salt, [Steven] moved on to piezo elements found in BBQ and cigarette lighters. These homemade speakers were much clearer than the chunk of Rochelle salt he was using previously, and surprisingly produced about the same audio quality as a commercially made piezo speaker [Steven] picked up at Radio Shack.

You can check out the build video for [Steven]‘s crystal speaker after the break.

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Turning on PC speakers whenever there is music playing

If you’re like a lot of people, most of the time your computer speakers are on without actually playing any music. This wastes a bit of power, and [Bogdan] thought he could create a circuit to cut down on that wasted electricity. The result is a very tiny auto-on circuit able fit inside a pair of speakers.

The circuit is built around the ATtiny13, very nearly the smallest microcontroller available with an on-board ADC. When music is played on the computer, the ATtiny senses a bit of voltage in the audio line and switches a relay to power the speaker.

Of course, there is always the problem of music with a high dynamic range; if the sound played from the computer has too low of a volume, the ATtiny might turn the speakers off even if music is playing. [Bogdan] solved this problem by adding a timer to his code; if nothing is detected by the ADC for three minutes, the speakers turn off.

Automatic speaker control via TV

[Jon] wanted his speakers to come on and off along with his TV. The speaker heats up if left on so he didn’t want to do that. But killing the power also resets the volume level (this is an old set of PC speakers and the remote is wired, not IR) so using one of those switched power strips was out as well. He thought a bit about trying to use the power LED on the TV to build his own circuit when it dawned on him. It’s possible to monitor the USB port on the TV and use it to switch on the speakers.

The circuit above uses a couple of opto-isolators to protect both the television and the speakers. The 5V line from the USB port on the back of the TV is monitored by an XNOR gate (which helps to filter out some of the toggling at power-on). When that gate latches it activates a 555 timer which in turn fires up the speakers. Presumable this happens when power is cut as well, but we’ll let you work through the circuit logic yourself.

Convert a speaker to a battery-powered amplifying party box

[Matt the Gamer] loved his pair of Minimus 7 bookshelf speakers. That is until a tragic hacking accident burned out the driver and left him with a speaker-shaped paper weight. But the defunct audio hardware has been given new life as a single portable powered speaker. Now he can grab it and go, knowing that it contains everything he needs to play back audio from a phone or iPod.

The most surprising part of the build is the battery. [Matt] went with a sealed lead-acid battery. It just barely fits through the hole for the larger speaker, and provides 12V with 1.2 mAh of capacity. He uses an 18V laptop power supply when charging the battery. The PSU is just the source, his own circuit board handles the charging via an LM317 voltage regulator. Also on the board is an amplifier built around a TDA2003A chip. He added a back panel which hosts connections for the charger and the audio input. Two switches allow the speaker to be turned on and off, and select between battery mode and charging mode. As a final touch he added a power indicator LED to the front, and a drawer pull as a carrying handle.

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