SDR Toolkit Bends Weather Station To Hacker’s Whims

December 17, 2021 by Tom Nardi 9 Comments

We probably don’t have to tell most Hackaday readers why the current wave of low-cost software defined radios (SDRs) are such a big deal for hackers looking to explore the wide world of wireless signals. But if you do need a refresher as to what kind of SDR hardware and software should be in your bag of tricks, then this fantastically detailed account from [RK] about how he hacked his La Crosse WS-9611U-IT weather station is a perfect example.

Looking to brush up his radio hacking skills, [RK] set out to use the ADALM-PLUTO software defined radio from Analog Devices to intercept signals between the La Crosse base station and its assorted wireless sensors. He notes that a $20 USD RTL-SDR dongle could do just as well if you only wanted to receive, but since his ultimate goal was to spoof a temperature sensor and introduce spurious data into the system, he needed an SDR that had transmit capabilities.

No matter your hardware, Universal Radio Hacker (URH) is the software that’s going to be doing the heavy lifting. In his write-up, [RK] walks the reader through every step required to find, capture, and eventually decode the transmissions coming from a TX29U wireless temperature sensor. While the specifics will naturally change a bit depending on the device you’re personally looking to listen in on, the general workflow is going to be more or less the same.

In the end, [RK] is not only able to receive the data coming from the wireless sensors, but he can transmit his own spoofed data that the weather station accepts as legitimate. Getting there took some extra effort, as he had to figure out the proper CRC algorithm being used. But as luck would have it, he found a Hackaday article from a couple years back that talked about doing exactly that, which help put him on the right path. Now he can make the little animated guy on the weather station’s screen don a winter coat in the middle of July. Check out the video below for a demonstration of this particular piece of radio prestidigitation.

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The Second Worst CAD Package Ever

December 17, 2021 by Dave Rowntree 28 Comments

A while back, [Heavydeck] remembered stumbling across the worst CAD package ever, which is a schematic editor whose existence was purely intended for use to make quick circuit sketches for documentation, presentations and the like. All good. But, being based on low quality JPEG graphics, which when blown up to projector size on a big screen, they look really rough. After deciding that the original nasty, clunky interface was just nasty and clunky enough, [Heavydeck] then proceeded to reimplement the idea over the course of an afternoon, and came up with Kludge (possibly the second worst CAD package ever) making an actually useful tool even more useful.

You see, whether you make website content, YouTube tutorials, or just need to write technical reports, if you’re in the electronics business, you’re going to need to make high-quality editable schematic images at some point, and Kludge might well solve some problems for you. Kludge lets you do so many things; you can save a schematic, you can load a schematic, you can even export it to an SVG file. Actually, that’s all you can do, but it is actually just enough. Once you’ve got an image as an SVG, you can whack that into Inkscape to add some more details and you’re done. We demonstrate this with the image above, which was not annoying at all to create.

So here’s to Kludging your way around a problem, and hoping that the somewhat limited symbol library may expand a little more in the future!

Error Codes And The Law Of Least Astonishment

December 17, 2021 by Al Williams 73 Comments

Do you know the law of least astonishment? I am not sure of its origin, but I first learned it from the excellent “Tao of Programming.” Simply put, it is the principle that software should always respond to the users in a way that least astonishes them. In other words, printing a document shouldn’t erase it from your file system.

Following the law of least astonishment, what should a program do when it hits a hard error? You might say that it should let the user know. Unfortunately, many systems just brush it under the rug these days.

I think it started with Windows. Or maybe the Mac. The thinking goes that end users are too stupid or too afraid of error codes or detailed messages so we are just leaving them out. Case in point: My wife’s iPhone wouldn’t upload pictures. I’m no expert since I carry an Android device, but I agreed to look at it. No matter what I tried, I got the same useless message: “Can’t upload photos right now. Please try again later.” Not only is this not very informative, but it also implies the problem is in something that might fix itself later like the network.

The real culprit? The iCloud terms of service had changed and she had not accepted the new contract. I have a feeling it might have popped up asking her to do that at some point, but for whatever reason she missed it. Until you dug into the settings and checked the box to agree to those terms, “later” was never going to happen.

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Christmas Lithophanes Make Neat Decorations

December 16, 2021 by Lewin Day 4 Comments

Lithophanes are neat little artistic creations that use variations in the thickness of a material to reveal an image when lit from behind. 3D printing is a great way to make lithophanes, and they can make for beautiful Christmas decorations, too!

It’s easy to make lithophane decorations for your Christmas tree with the help of the ItsLitho tool. The online application takes any image you upload, and can generate lithophane geometry that you can 3D print at home. Print your custom bell or bauble, add the printed hooks, and then the final decoration can be backlit to reveal its image by inserting an LED from a string of Christmas lights.

The result is a beautiful, glowing decoration that displays a detailed image when lit up. All you need is a few images and a 3D printer to produce decorations as unique gifts for your family and friends.

We’ve seen the technique put to other uses too, such as in this convincing lamp designed after our very own Moon. Video after the break.

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A Programming Language To Express Programming Frustration

December 14, 2021 by Bryan Cockfield 26 Comments

Programming can be a frustrating endeavor. Certainly we’ve all had moments, such as forgetting punctuation in C or messing up whitespace in Python. Even worse, an altogether familiar experience is making a single change to a program that should have resulted in a small improvement but instead breaks the program. Now, though, there’s a programming language that can put these frustrations directly into the code itself into a cathartic, frustration-relieving syntax. The language is called AHHH and it’s quite a scream.

While it may not look like it on the surface, the language is Turing complete and can be used just like any other programming language. The only difference is that there are only 16 commands in this language which are all variants of strings of four capital- or lower-case-H characters. The character “A” in the command “AHHH” starts the program, and from there virtually anything can be coded as a long, seemingly unending scream. The programming language is loosely related to COW which uses various “moos” to create programs instead of screams, and of course is also distantly related to brainfuck which was an esoteric programming language created in order to have the smallest possible compiler.

We can’t really recommend that beginner programmers start to learn this language instead of something more practical like Python, esoteric languages like these can teach us a lot about the way that computers work. This language, for example, lets you code in pixels instead of characters. Others are more for fun such as this language which turns your code into an ’80s rock ballad.

Thanks to [Kyle F] for the tip!

Apple Falling Division

December 9, 2021 by Al Williams 23 Comments

[Paul Curtis] over at Segger has an interesting series of blog posts about calculating division. This used to be a hotter topic, but nowadays many computers or computer languages have support for multiplication and division built-in. But some processors lack the instructions and a library to do it might be less than ideal. Knowing how to roll your own might allow you to optimize for speed or space. The current installment covers using Newton’s algorithm to do division.

Steve Martin had a famous bit about how to be a millionaire and never pay taxes. He started out by saying, “First… get a million dollar. Then…” This method is a bit like that since you first have to know how to multiply before you can divide. The basic premise is twofold: Newton’s method let you refine an estimate of a reciprocal by successive multiplications and then multiplying a number a reciprocal is the same as dividing. In other words, if we need to divide 34 by 6, you could rewrite 34/6 to 34 * 1/6 and the answer is the same.

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Cracking The Spotify Code

December 7, 2021 by Matthew Carlson 4 Comments

If you’ve used Spotify, you might have noticed a handy little code that it can generate that looks like a series of bars of different heights. If you’re like [Peter Boone], such an encoding will pique your curiosity, and you might set out to figure out how they work.

Spotify offers a little picture that, when scanned, opens almost anything searchable with Spotify. Several lines are centered on the Spotify logo with eight different heights, storing information in octal. Many visual encoding schemes encode some URI (Uniform Resource Identifier) that provides a unique identifier for that specific song, album, or artist when decoded. Since many URIs on Spotify are pretty long (one example being spotify :show:3NRV0mhZa8xeRT0EyLPaIp which clocks in at 218 bits), some mechanism is needed to compress the URIs down to something more manageable. Enter the media reference, a short sequence encoding a specific URI, generally under 40 bits. The reference is just a lookup in a database that Spotify maintains, so it requires a network connection to resolve. The actual encoding scheme from media reference to the values in the bars is quite complex involving CRC, convolution, and puncturing. The CRC allows the program to check for correct decoding, and the convolution enables the program to have a small number of read errors while still having an accurate result. Puncturing is just removing bits to reduce the numbers encoded, relying on convolution to fill in the holes.

[Peter] explains it all in his write-up helpfully and understandably. The creator of the Spotify codes stopped by in the comments to offer some valuable pointers, including pointing out there is a second mode where the lines aren’t centered, allowing it to store double the bits. [Peter] has a python package on Github with all the needed code for you to start decoding. Maybe you can incorporate a Spotify code scanner into your custom Spotify playing mini computer.