Update: Home Security Monitoring Prototype

July 29, 2013 by Mike Szczys 8 Comments

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This project is about home security monitoring, but the update is crack for electronics designers. [Simon Ludborzs] continues to work on his prototype and he’s fantastic about sharing his success and failure in a conversational manner.

In April we saw his initial design which combined a SIM900 GSM modem with his own board to let him monitor his home security system without hiring a monthly service. Above you can see a snap of his latest prototype. It’s not fully populated as he’s testing the power supply… which in this state puts out 0V. Obviously that’s not up to his design specification so he started hunting around for the issue. He tells a tale of woe which is near to our hearts. He removed Q6, which is BC807 transistor, in order to test the FET used on the board. This brought it to life and had him looking into the datasheet of the part and its footprint in Altium. The footprint is right, the schematic symbol is wrong. There’s a lucky fix though. Above you can see the original design. The fix was just to rotate the part. This is illustrated as a change in the layout, but it worked with the original pad location. They’re not square to the transistor’s legs but they do still fit the outline.

He goes on to stress test the PSU output and then discuss whether it’s enough for the rest of the project. All in all a fascinating read!

Polishing Optics Milled From Acrylic

July 23, 2013 by Mike Szczys 11 Comments

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[Ben Krasnow] milled some lenses out of cast acrylic and needed a way to get an optical finish on the tool-marked surface. He tested several acrylic finishing methods to achieve a crystal clear finish. The tests were done using flat chunks. A regiment of sandpaper, from coarse to fine, was used as the first stage of the operation. From there [Ben] sought out the best finishing step, starting with hand polishing tests, flame polishing, and methylene chloride vapor polishing (which is something along the lines of acetone vapor polishing for 3D printed ABS parts).

Flame polishing and vapor polishing are not really exact sciences… at least in the tests he performed. It was difficult to know exactly how long to expose the acrylic. Too short or too long resulted in poor clarity. Watch his video to get a look at all results. We’d say the the easiest way to make milled acrylic clear without achieving an optical finish is to flame polish it as it doesn’t really require that you sand it ahead of time. But [Ben’s] tests prove that you can’t beat hand polishing with 600 then 2000 grit sandpaper before finishing up with a liquid plastic polish.

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Reverse Engineer A PSU To Change Its Output Voltage

July 20, 2013 by Mike Szczys 33 Comments

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[Semicolo] has a bunch of old PSUs on hand which he pulled out of some Lexmark dot matrix printers. In their stock form they put out 40V, which is close to the 35V max he needs to run the stepper motors on a 3D printer he’s been building. So he reverse engineered the PSU to change its output.

On the left you can see the top of the PCB. [Semicolo] flipped it over and snapped a picture of the traces on the bottom of the board. With a bit of work in The Gimp (FOSS image editing software) he was able to convert the traces to black and white. Overlaying the picture of the top with a 50% transparency of the traces made it rather easy see the connections and generate a schematic for the hardware. That’s a really cool trick!

Figuring out how it’s supposed to work is a big step in achieving his goal. The next step was to see if he could bend the circuit to his will. He had previously run across ATX PSU hacks which changed the reference voltage in order to alter the output. He grabbed a datasheet for the HA17431 variable shunt regulator. It lays out how to tune the output based on values of a few external components. He dropped in one resistor and the output measured 31V, well within his target range.

Interviews With The Hand-Makers

July 19, 2013 by Mike Szczys 2 Comments

Want some inspiration to launch your own Handmade adventure? [Anne Hollowday] wrote in to share a series of short films she’s been posting called Makers of Things.

So far there are just four episodes but we hope she makes many more. Above you can see the latest, entitled Woodworker. It’s a monologue-style interview with masters of their crafts. The first installment looks at an engineering club called SMEE that builds a wide range of intricately engineered things like clocks. There’s another maker who builds miniature models of machines. And of course, The Problem Solver whose high-tech endeavors parallel the subjects of interest found on our main site.

How Can The Net Amount Of Entropy Of The Universe Be Massively Increased?

July 16, 2013 by Brian Benchoff 74 Comments

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The greatest – and last – question that will ever be asked is, “How can the net amount of entropy of the universe be massively decreased”. It follows then, that the worst – and possibly first – question ever asked is, “How can the net amount of entropy of the universe be massively increased?” While for the former question there’s insufficient data for a meaningful answer, we’ve found the answer to the latter question. It’s a machine designed to waste energy, and the exact opposite of a perpetual motion machine.

The machine is set up along two stories of a building, with cables, pulleys, and levers constantly pressing an elevator button. The device is powered by the elevator doors opening, so when the elevator opens of the first floor, the part of the machine on the second story calls the elevator. This repeats ad infinitum.

Wait. It gets better. Inside the elevator car, there’s a modified printing calculator also powered by the elevator doors. Every time the doors open, it calculates the amount of energy consumed for each cycle of the elevator. It’s a hydraulic elevator without a countersink, so moving down is effectively free, but each cycle of the elevator still uses up 11.8 Kilojoules of the universe’s energy. To make the build a complete waste of resources, the printing calculator neatly empties it’s printed tape into a wastepaper bin.

We’re tempted to call this a [Rube Goldberg] machine, but that doesn’t seem to fit this machine that does absolutely nothing. Calling it a useless box is more fitting, but this is far, far more impressive than a box that turns itself off. Whatever it is, you can see a video of it in action below.

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The Tiniest Arcade Cabinets You’ve Ever Seen

July 11, 2013 by Brian Benchoff 25 Comments

After perusing Amazon one day, [Dave] found a very interesting piece of kit: a small, 1.5″ digital picture frame. They’re not very complex, just an LCD, a few buttons to cycle the picture, and a battery to keep everything portable. He decided the best use of this tech would be a tiny arcade cabinet, featuring screen shots of the best games a darkly neon lit arcade of the late 80s had to offer.

After sourcing a few of these digital picture frames on eBay, [Dave] set to work disassembling the frames and designing a custom enclosure. He wanted a few specific features: controls in the right place, replaceable sides, and the glowing red eyes of a coin acceptor slot. [Dave] whipped a model up in OpenSCAD and sent the parts over to his printer.

The controls for the digital picture frame were connected to a quartet of tact switches on the control panel, and a red LED provides the glow from the coin acceptor. With a USB plug and the frame’s memory loaded up with screen shots, [Dave] has a fabulous desk toy.

All the relevant files are up on Thingiverse if you’d like to build your own.

Best Practices To Include In Your Final Projects

July 9, 2013 by Mike Szczys 41 Comments

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Making that final push to button up your projects can be a bit daunting. It’s kind of like the punch list on a construction project — add switch plates, fill nail holes in baseboards, screw in light bulbs, clean windows — that stuff adds up quickly. But having a set of best practices in mind throughout the development phase will cut down on that burden. [Caleb P.] just published a quick guide using a recent project as an example.

First and foremost is the label seen on the project box lid. How many times have you pulled out a circuit board from a year or two earlier and not been able to figure out the pinout? As with ancient televisions and radios, including the service schematic will save you big time! He also mentions that the size and orientation of the components in the case was in the back of his mind the whole time. That paid off because everything fits like a glove. [Caleb] makes sure the battery is easy to get to, and the each component has some type of connector so that it may be removed and serviced/replace without soldering. There’s certainly nothing groundbreaking in this guide. But ask yourself: have I been following all of these guidelines in my own work?