Web-enabled Kinect

There are Kinect hacks out there for robot vision, 3D scanners, and even pseudo-LIDAR setups. Until now, one limiting factor to these builds is the requirement for a full-blown computer on the device to deal with the depth maps and do all the necessary processing and computation. This doesn’t seem like much of a problem since [wizgrav] published Intrael, an HTTP interface for the Kinect.

[Eleftherios] caught up to [wizgrav] at his local hackerspace where he did a short tutorial on Intrael. [wizgrav]’s project provides each frame from the Kinect over HTTP wrapped up in JSON arrays. Everything a Kinect outputs aside from sound is now easily available over the Internet.

The project is meant to put computer vision outside the realm of desktops and robotic laptops and into the web. [wizgrav] has a few ideas on what his project can be used for, such as smart security cameras and all kinds of interactive surfaces.

After the break, check out the Intrael primer [wizgrav] demonstrated (it’s Greek to us, but there are subtitles), and a few demos of what Intrael ‘sees.’

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Exterior-grade electrical box as project enclosure

The quest for a project box is always a balance between cost, complexity, and style. We think [Pcmofo] really finds the mark with his exterior electrical box enclosures. He took the time to document his fabrication process for those that want to replicate his look.

These grey plastic boxes are meant to keep the elements away from home and commercial electrical systems. They’re easy to find and come in many different sizes (this one is 8″ square and 4″ deep). The plastic is very rigid, but still easy enough to work with simple tools.

[Pcmofo] starts by eyeballing the placement of his components. Once he has a good idea of where each should be located he grabs a caliper and uses Adobe Illustrator or Inkscape to design a template. This is attached with painter’s tape, and rough openings are made using a drill press. The holes are brought to the final size by hand using files for a nice finished edge. When it comes time to mount hardware, the plastic is strong enough to hold threads if you are careful when using the tap to cut them.

The example enclosure houses a temperature controller for fermenting beer. You can see some video of the enclosure embedded after the break.

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Echo box shakes itself to make sound

The echo box performs exactly as its name implies. If you tap out a rhythm on the lid, it will tap the same thing back to you. Except it isn’t tapping to make the sound, but vibrating.

The concept is similar to the Knock Block. In that hack, a piezo element detected a rapping on the wooden enclosure and repeated the rhythm by striking the lid with a solenoid. This iteration also uses a piezo element as the sensor. In the image above you can see a segment of PVC pipe in the upper corner. That houses the element, sandwiched between two pieces of wine bottle cork. That cork just touches the lid of the box, transferring the vibrations to the element.

The sound is created by a motor with an offset weight on its spindle. When the motor spins, it causes vibrations. The enclosure is one wood box inside of another, so the vibrating motor cause the inner box to shake against the outer one to make noise. Hear it for yourself in the clip after the break.

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Reverse voltage protection with a P-FET

[Afroman’s] latest video shows you how to add reverse voltage protection with minimal power loss. At some point, one of your electronic concoctions will turn out to be very useful. You want to make sure that a battery plugged in the wrong way, or a polarity mistake with your bench PSU doesn’t damage that hardware. It’s easy enough to plop in a diode for protection, but as [Afroman] points out, that wastes power in the form of heat when the circuit is working correctly. His solution is to add a P channel MOSFET which only allows power to flow when the polarity of the source voltage is correct.

The schematic above shows the P-FET on the high side of the circuit. The gate is hooked to ground, allowing current to move across the DS junction when the battery is connected. This design also uses a clamping diode to keep the gate voltage within a safe range. But there are P-FETs out there that wouldn’t need that diode or resistor. This method wastes ten times less power than a simple diode would have.

We’ve embedded the video after the break where [Afroman] shares the math and reasoning behind his component choices.

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Sound treating a studio

Looks like [Dino] is getting the band back together. After a junkyard tube amp and a DIY tremolo stompbox, he’s back again, this time doing a bit of sound treatment in his studio.

Most rooms naturally have a bit of flutter echo. You’ll notice this when you move into an apartment or new house – rooms sound a lot more cavernous without rugs, drapes and furniture. Unfortunately, having a bunch of couches doesn’t bode well for the workflow in a studio despite what MTV Cribs may have told us. The usual solution is to put up some sound-absorbing material on the walls, and a metric ton of cardboard egg cartons don’t work.

[Dino] found a bunch of acoustic panels his neighbor threw out during a renovation (yes, we know, he’s very lucky). After doing some pre-installation tests, the panels were hung. Afterwards, the amount of echo was drastically reduced.

The good news is we finally get a look inside [Dino]’s studio. We saw the junkyard tube amp we covered earlier, but not the neat tremolo pedal he made.

Check out [Dino]’s video of sound treating a room after the break.

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AVR External Memory Interface (XMEM) reads input matrix

Reading from a large number of inputs, like this piano keyboard, can be tedious. Even when multiplexing there’s a lot to keep track of. But if you choose the right microcontroller, you may have hardware assistance. Here’s an ATmega640 is using it’s external memory interface to read the key matrix.

You may remember the Open Music Labs article about reading from a shift register using just one pin of a microcontroller. This time around a shift register is still used, but instead of pulling in a long line of parallel inputs, the switches are multiplexed to reduce the number of I/O pins used to read them.

A 74HC573 is used to facilitate the multiplexing. We won’t go into how that part is accomplished; there’s a separate post that explains the process. What’s unique here is that the XMEM peripheral of the AVR microcontroller is used to grab the data. This is intended for external memory chips, but if you get the timing just right, it greatly simplifies reading in a matrix of up to 128 inputs.

Playing classic 60s tunes with an all electronic band


If you are considering repurposing some old computer equipment to create music, be aware that the bar has been raised just a tad. YouTube user [BD594] spent some time sifting through his bin of used electronics and put together a 5-piece band that plays a pretty awesome rendition of The Animals’ “House of the Rising Sun”.

Last week, we saw a pretty impressive hack with a floppy drive that could bang out music using a calculator, but this takes things to a whole new level. [BD594] used an old HP ScanJet to simulate the song’s vocals, while an Atari 800XL combined with an oscilloscope is used as an organ. A Ti-99/4a is used in conjunction with another scope to play guitar notes, while a PIC-controlled hard drive does double duty, playing both the bass drum and cymbals.

We dare you to watch the video below and NOT be thoroughly impressed with his work.

[BD594] says that once he has a bit of free time, he’ll be putting out another video – something we’ll be anxiously waiting to see.

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