Rubber Duck Debugging The Digital Way

June 10, 2018 by Dan Maloney 16 Comments

Anyone who slings code for a living knows the feeling all too well: your code is running fine and dandy one minute, and the next minute is throwing exceptions. You’d swear on a stack of O’Reilly books that you didn’t change anything, but your program stubbornly refuses to agree. Stumped, you turn to the only one who understands you and pour your heart out to a little yellow rubber duck.

When it comes to debugging tools, this digital replacement for the duck on your desk might be even more helpful. Rubber duck decoding, where actually explaining aloud to an inanimate object how you think the code should run, really works. It’s basically a way to get you to see the mistake you made by explaining it to yourself; the duck or whatever – personally, I use a stuffed pig– is just along for the ride. [platisd] took the idea a step further and made his debugging buddy, which he dubs the “Dialectic Ball,” in the form of a Magic 8-Ball fortune teller. A 3D-printed shell has an ATtiny84, an accelerometer, and an LCD screen. To use it, you state your problem, shake it, and read the random suggestion that pops up. The list has some obvious suggestions, like adding diagnostic print statements or refactoring. Some tips are more personal, like talking to your local guru or getting a cup of coffee to get things going again. The list can be customized for your way of thinking. If nothing else, it’ll be a conversation piece on your desk.

If you’re more interested in prognostication than debugging, we have no shortage of Magic 8-Ball builds to choose from. Here’s one in a heart, one that fits in a business card, and even one that drops F-bombs.

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Donut vending machine without microcontroller

No Microcontroller In This Vending Machine, D’oh!

June 9, 2018 by Steven Dufresne 28 Comments

You might think that a microcontroller would be needed to handle a vending machine’s logic. For one thing, only the correct change should activate them and the wrong change should be returned. If the correct change was detected then a button press should deliver the right food to the dispenser. But if you like puzzles then you might try to think of a way to do with without a microcontroller. After all, the whole circuit can be thought of as a few motors, a power source, and a collection of switches, including the right sized coin.

That’s the way [Little Puffin] approached this donut dispensing vending machine. What’s really fun is to watch the video below and wonder how the logic will all come together as you see each part being put in place. For example, it’s not until near the end that you see how the coin which is a part of the circuit is removed from the circuit for the next purchase (we won’t spoil it for you). Coins which are too small are promptly returned to the customer. To handle coins which are the right size but are too heavy, one enhancement could be to make them fall through a spring-moderated trap door and be returned as well. We’re not sure how to handle coins which are the right size but too light though.

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Magnetic Spheres Line Up For Rotary Encoder Duty

June 5, 2018 by Dan Maloney 21 Comments

When it comes to rotary encoders, there are plenty of options. Most of them involve putting a credit card number into an online vendor’s website, though, and that’s sometimes just not in the cards. In that case building your own, like this encoder using magnetic spheres, is a pretty cool way to go too.

If he’d had less time to spare, we imagine [Antonio Ospite] would have gone for a commercial solution rather than building an encoder from scratch. Then again, he says his application had noise considerations, so maybe this was the best solution overall. He had some latching Hall effect sensors lying around, but lacked the ring magnet that is usually used with such sensors in magnetic encoders. But luckily, he had a mess of magnetic spheres, each 5 mm in diameter. Lined up in a circle around a knob made from a CD spindle, the spheres oriented themselves with alternating poles, which is just what the Hall sensors want to see. The sensors were arranged so the pulses are 90° apart, and can resolve 4.29° steps. Check out the video below to watch it work.

Small, cheap and effective are always good things. But magnets aren’t the only thing behind homebrew rotary encoders. A couple of microswitches might do in a pinch, or maybe even scrapped hard drives would suffice.

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Buck Converter Efficiency

June 2, 2018 by Al Williams 10 Comments

We always appreciate when someone takes the time to build something and then demonstrates what different design choices impact using the real hardware. Sure, you can work out the math and do simulations, but there’s something about having real hardware that makes it tangible. [Julian Ilett] recently posted two videos that fit this description. He built a buck converter and made measurements about its efficiency using different configurations.

The test setup is simple. He monitors the drive PWM with a scope and has power meters on the input and output. That makes it easy to measure the efficiency since it is just the ratio of the power output to input. You can see the two videos, below.

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An Electromagnet Brings Harmony To This Waving Cat

June 1, 2018 by Kerry Scharfglass 9 Comments

We’ve noticed waving cats in restaurants and stores for years, but even the happy bobbing of their arm didn’t really catch our attention. Maybe [Josh] had seen a couple more than we have when it occurred to him to take one apart to see how they work. They are designed to run indoors from unreliable light sources and seem to bob along forever. How do the ubiquitous maneki-neko get endless mechanical motion from one tiny solar cell?

Perhaps unsurprisingly given the prevalence and cost of these devices, the answer is quite simple. The key interaction is between a permanent magnet mounted to the end of the waving arm/pendulum and a many-turn wire coil attached to the body. As the magnet swings over the coil, its movement induces a voltage. A small blob of analog circuitry reacts by running current through the coil. The end effect is that it “senses” the magnet passing by and gives it a little push to keep things moving. As long as there is light the circuit can keep pushing and the pendulum swings forever. If it happens to stop a jolt from the coil starts the pendulum swinging and the rest of the circuit takes over again. [Josh] points to a similar circuit with a very nice write up in an issue of Nuts and Volts for more detail.

We’ve covered [Josh]’s toy teardowns before and always find this category of device particularly interesting. Toys and gadgets like the maneki-neko are often governed by razor-thin profit margins and as such must satisfy an extremely challenging intersection of product constraints, combining simple design and fabrication with just enough reliability to not be a complete disappointment.

For more, watch [Josh] describe his method in person after the break, or try flashing his code to an Arduino and make a waving cat of your own.

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Blowing Arcylic Canopies Using Stuff From Around The Shop

May 31, 2018 by Steven Dufresne 13 Comments

Blowing an acrylic sheet after heating it is an easy way to make a smooth and transparent canopy or bubble for anything from clams to light fixtures. [Michael Barton-Sweeney] does it using plastic blow ovens he made cheaply, mainly from stuff which most of us already have in our workshops.

All you need is a way to heat the plastic, to then clamp it down around the edges, and finally to blow air into it as you would when blowing up a balloon. Of course, there are things to watch out for such as making sure the plastic is heated evenly and letting it cool slowly afterward but he covers all that on his hackaday.io page.

He’s also on his second plastics blow oven. The first one worked very well and is perhaps the easiest to make, building up an enclosure of CMUs (cinder blocks) and brick. He had success heating it with both propane and with electric current run through Kanthal wire. But the CMUs absorbed a lot of heat, slowing down the process. So for his second one he made a cast concrete enclosure with aluminum reflectors inside to focus the heat more to where needed.

We’re not sure of everything he’s blown acrylic bubbles for but we first learned of his ovens from the transparent clams in his underwater distributed sensor network. In fact, he was inspired to do plastics blowing from a childhood memory of the Air Force museum in Dayton, Ohio, where they visited the restoration hanger and watched the restorers blowing bubbles for a B-17 ball turret.

Though if you want to go smaller and simpler for something like a light fixture then you can get away with using a toaster oven, a PVC pipe, and a toilet flange.

Cheap Stuff To Hack: A Router With An SDR For $13

May 30, 2018 by Brian Benchoff 41 Comments

The history of consumer electronics is littered with devices that are relatively uninteresting at first, but become spectacular platforms for hardware exploitation once a few select people figure out how everything ticks. The Linksys WRT54G was just a router until someone figured out how to put a complete Linux system on them. Those RTL-SDR dongles were just for capturing over the air TV until someone realized they were actually a software-defined radio. The CueCat was just dot-com boom marketing garbage until… well, we picked up a lot of CueCats regardless.

Now there’s a new device sitting on the shelves at Walmart just waiting for some Linux hackers to have a go. It’s the Tzumi MagicTV, a device that allows you to watch over-the-air television on your phone. What’s inside? It’s a WiFi router, an RTL-SDR, and a battery pack in one tiny package. The best part? It costs $13, and apparently Walmart is just blowing them out.

Right now, there aren’t too many details on what’s going on inside the Tzumi MagicTV box, however, the discussion over on the RTLSDR subreddit has revealed enough to give us a good idea of what’s going on. The router inside the MagicTV is a TP-Link TL-WR703N, the exact same WiFi router that took the WRT54G’s place as the king of hackable routers a few years ago. The SDR chip is the same as the Astrometa DVB-T2, one of the common TV tuners on-a-stick. Other than that, there are TX and RX pins on the board, SSH is open, no one knows the password, but as of this writing, a few people are putting John the Ripper to work trying to break into this box.

What is the end goal of cracking this Linux box wide open? Well, it’s a WiFi router and an SDR, so if you want to make your own Flightaware ADS-B logger, that could be on the table. Of course, you could actually use it for its intended purpose and pull down over-the-air TV to your local network, but that seems so pedestrian after getting root on a $13 box from Walmart.

Thanks [Adam] for the tip!