Smart Mirror Reflects Hacker

Did [TobiasWeis] build a mirror that’s better at reflecting his image? No, he did not. Did he build a mirror that’s better at reflecting himself? We think so. In addition to these philosophical enhancements, the build itself is really nice.

The display is a Samsung LCD panel with its inconvenient plastic husk torn away and replaced with a new frame made of wood. We like the use of quickly made 3D printed brackets to hold the wood at a perfect 90 degrees while drilling the holes for the butt joints. Some time with glue, band clamps, and a few layers of paint and the frame was ready. He tried the DIY route for the two-way mirror, but decided to just order a glass one after some difficulty with bubbles and scratches.

A smart mirror needs an interface, but unless you own stock in Windex (glass cleaner), it is nice to have a way to keep it from turning into an OCD sufferer’s worst nightmare. This is, oddly, the first justification for the Leap Motion controller we can really buy into. Now, using the mirror does not involve touching the screen. [Tobias] initially thought to use a Raspberry Pi, but instead opted for a mini-computer that had been banging around a closet for a year or two. It had way more go power, and wouldn’t require him to hack drivers for the Leap Motion on the ARM version of Linux.

After that is was coding and installing modules. He goes into a bit of detail about it as well as his future plans. Our favorite is programming the mirror to show a scary face if you say “bloody mary” three times in a row.

Materials To Know: Baltic Birch

Long ago, when I wanted a plywood sheet, I would go to the local big box hardware store and buy whatever was at the center of the optimization curve for  cheapest and nicest looking. I would inevitably suffer with ultra-thin veneers on the top, ugly cores, unfinishable edges, warping, voids, and other maladies of the common plywood. One day I said enough is enough and bothered the salesman at my local lumber supply until he showed me one that wasn’t awful.

There are subtle clues that the Baltic Birch I've purchased is Russian.
There are subtle clues that the Baltic Birch I’ve purchased is Russian.

Baltic birch differs from other plywoods in a few ways. Regular plywood is usually made locally from the cheapest possible core wood in alternating grain layers laminated together with a hardwood veneer on the top. There are interior and exterior grades. The exterior grades are usually made with a different glue, but don’t necessarily denote a higher quality or stability. Some of the glues used can be toxic. Wear a respirator. In normal plywood, the ATSM or BB standards only apply to the face veneers used to finish the product. The core can be of whatever quality is convenient for the manufacturer.

True Baltic Birch is made in the Baltic Region with the biggest producers being Russia and Finland. Outside of the US it is sometimes called Finnish Birch or Russian Birch plywood for this reason. It is made from only top quality birch veneers laminated together with no filler wood. It is also unique in the care taken to make sure each layer of the wood is patched so there are no voids. All Baltic Birch is made with exterior grade glue, and when properly sealed will work for outdoor applications. There are grades of Baltic birch for marine applications and exceptionally void free aircraft grade plywood at a much higher cost.

The easiest way to spot Baltic Birch if you’re American is its form factor. Baltic birch comes in 1525 x 1525 mm squares, which approximates to 5 ft x 5 ft. Some people have said that manufacturers have started to produce 4 ft x 8 ft sheets specifically for the North American market, but this information comes with a caveat that these are usually lower grades made locally or in China parading under the name. The metric form factor extends to the thicknesses of the sheets. In America they will be sold as inch, but fit pretty closely to a metric form.

  • 3 mm ≈ 1/8″ (3 plies)
  • 6 mm ≈ 1/4″ (5 plies)
  • 9 mm ≈ 3/8″ (7 plies)
  • 12 mm ≈ 1/2″ (9 plies)
  • 18 mm ≈ 3/4″ (13 plies)
    – From [3] Ultimate guide to Baltic birch.
The core of regular hardware store plywood.
The core of regular hardware store plywood. Pretty bad in comparison.

There are some really nice practical features of Baltic Birch. One of my favorites is the absolute uniformity of the layers. This means that two pieces of birch can be laminated together and the seam between the two becomes indistinguishable. I’ve used this to make cases by CNC routing out the inside of a sheet of Baltic birch, drilling some holes for alignment pins, and then laminating the whole assembly together. We’ve covered a few readers who have had similar ideas. Since the layers are uniform you can also do interesting things when combined with a CNC router. For example, carefully milling away the layers you can get a topographic map of the object.

Baltic Birch is also significantly flatter and more stable than other plywood options. It is commonly the material used for fences on expensive tables saws. It moves less during temperature swings and changes in ambient moisture. This is one of the reasons it’s popular with fine furniture builders. This also makes Baltic birch a good option for home CNC builds, certainly better than MDF . Due to the higher quality wood and better manufacturing it is quite strong as well. It is a great structural wood.

Explanation of the grading scale for Baltic Birch from [1] Dan’s hobbies.
Baltic birch holds stains very well on both its faces and its edges. It’s as easy to paint and glue as any wood. As far as surface finish goes it’s important to note that as mentioned previously, Baltic Birch is graded to a different scale than regular plywood. The grades will determine how the face veneers are treated. B/B is the highest grade with both sides being defect free. B/BB is much more common and is what you are likely to find. I have not found C or CP grades in the US. My guess is that we have plenty of low grade plywoods to compete with it. It is likely found nearer to the areas where it is produced.

This is on the non-finishing side of a Baltic Birch panel. You can see the care taken to fix knots and voids.
This is on the non-finishing side of a Baltic Birch panel. You can see the care taken to fix knots and voids. This will be done through the whole sheet. The face of the board will not have marks. This is a B/BB grade sheet. If it was B/B both sides would be without patches.

Baltic birch is more expensive than the regular grade stuff. So a sheet of ¾” thick Oak veneer plywood with a pine core, interior grade, from Lowes is about 35 US dollars where a similar sheet of 18mm Baltic Birch will run around 65 dollars.

I’ll still occasionally purchase a cheaper sheet of plywood when I have a non-critical application (like garage shelving), but when I am doing something precise or nice I’ll spend the extra on the birch plywood. While I love this material, I am by no means a wood worker. Have any of you had experience with this plywood? Is there an even better plywood out there?

I’ve left my sources below for further reading. [3] Ultimate Guide to Baltic Birch is very good.

[1] Dan’s Hobbies. (2016). A baltic birch plywood primer | Dan’s Hobbies. [online] Available at: [Accessed 19 Apr. 2016].

[2]Wikipedia. (2016). Plywood. [online] Available at: [Accessed 19 Apr. 2016].

[3] Stephens, (2014). Ultimate Guide to Baltic Birch Plywood: Why It’s Better, When to Use It |. [online] Available at: [Accessed 19 Apr. 2016].

DIY Vacuum Chamber Proves Thermodynamics Professor Isn’t Making It All Up

[Mr_GreenCoat] is studying engineering. His thermodynamics teacher agreed with the stance that engineering is best learned through experimentation, and tasked [Mr_GreenCoat]’s group with the construction of a vacuum chamber to prove that the boiling point of a liquid goes down with the pressure it is exposed to.

His group used black PVC pipe to construct their chamber. They used an air compressor to generate the vacuum. The lid is a sheet of lexan with a silicone disk. We’ve covered these sorts of designs before. Since a vacuum chamber is at max going to suffer 14.9 ish psi distributed load on the outside there’s no real worry of their design going too horribly wrong.

The interesting part of the build is the hardware and software built to boil the water and log the temperatures and pressures. Science isn’t done until something is written down after all. They have a power resistor and a temperature probe inside of the chamber. The temperature over time is logged using an Arduino and a bit of processing code.

In the end their experiment matched what they had been learning in class. The current laws of thermodynamics are still in effect — all is right in the universe — and these poor students can probably save some money and get along with an old edition of the textbook. Video after the break.

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A Polymer Concrete DIY CNC With No Perceptible Budget In Sight

The Jargon File describes a wizard as someone who groks something to a very high degree, or the kind of person that builds a polymer concrete CNC machine with a pneumatic tool changing spindle that they designed by themselves.  It makes you think that maybe Tony Stark COULD build it in a cave with scraps.

It’s a five part video series showing snippets of the build process. The last video gives an overview of the design of the machine. It is all very much in German, so if you speak German and we got anything wrong about the machine or missed anything cool, please fill us in down in the comments.

The machine starts with a 1500 kg polymer concrete pour with some steel stock embedded in it. It is then machined within an inch mm of its life as shown by practically zero deviation over its length when measured against a granite block. The wizard then goes on to make his own spindle, get castings made, and more. We liked his flowery kitchen hotplate, which he used to heat the bearings for an interference fit. It added a certain amount of style.

Unfortunately the videos don’t show the machine running, but we assume this sort of person is happily building arc reactors, power suits, and fighting crime. They probably don’t have time to film “CNC Bearbeitungszentrum im Eigenbau Teil 5”. Videos after the break.

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DIY Spot Welder Doesn’t Look Like it Will Immediately Kill You

We love hacks that involve mains voltage, but most of the time, for safety’s sake, we secretly hope for that one macabre commenter that details every imaginable way the questionable design choices will result in death. This spot welder may still be dangerous, but it looks like they took some precautions to make it non-lethal, and that counts for a lot.

After their extremely questionable high speed belt sander, this one is, refreshingly, extremely well done. It starts of as a dead standard microwave spot welder build: take apart microwave, try not to die from large capacitor, remove coil, modify coil, and hook up.

After that, it gets to some nice heavy metal music fabrication. Aside from a slightly shocking number of fresh OSHA reportable hand injuries (wear gloves!) the build goes together well. A lot of planning obviously went into it, from the actively cooled transformer to what appears to be a resettable timer circuit for the weld duration, not to mention the way that it just fit together so well at the end. There were some neat ideas as far as home mechanics go that we’ll be using in some of our projects.

In the end, the proof is in the spot-weld. The timer is set, pedal gets pressed down, and when tested, the sheet metal breaks instead of the weld. Video after the break.

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Small Experiments in DIY Home Security

[Dann Albright] writes about some small experiments he’s done in home security.

He starts with the simplest. Which is to purchase an off the shelf web camera, and hook it up to software built to do the task. The first software he uses is the free, iSpy open source software. This adds basic features like motion detection, time stamping, logging, and an interface. He also explores other commercial options.

Next he delves a bit deeper. He starts by making a simple motion detector. When the Arduino detects motion using a PIR sensor it gets a computer to text an alert. After the tutorial begins to veer a little and he adds his WiFi light bulbs to the mix. Now he can send an email and change the color of the lights.

We suppose, that from a security standpoint. It would really freak a burglar out if all the lights turned red when they walked into a room. Either way, there’s definitely a fun weekend project in playing around with all these systems.

DIY Arduino Watch

We first thought [Alexis Ospitia]’s watch was a sports watch made with an Arduino, but it’s actually a sporty watch made with an Arduino. This explains the watch’s strange ability to tell you the current temperature and humidity.

The core of the watch is an Arduino Mini. To make it good for time telling, a real-time clock module was added. A DHT11 monitors the temperature and humidity. A charge circuit and lithium battery provide power. Finally, the watch displays the date, time, and other data with an LCD from a Nokia 5110. We can tell you the last part that’s going to break on this.

Even if you think the watch is a bit chunky, the tutorial is very slick. [Alexis] has taken the trouble to individually draw and describe each portion of the watch’s construction. He explains each pin, what they do, and provides a Fritzing drawing of the wires to the Arduino. The code is provided; to program the watch a USB-to-serial module must be used.

For the housing he made a box from a thin gauge aluminum sheet and attached leather straps to the assembly. The final construction is cool looking in a techno-punk way, and is fairly compact. One might even say sporty.