Cryptanalyse Your Air Con

Infrared remote controls are simple and ubiquitous. Emulating them with the aid of a microcontroller is a common project that hackers use to control equipment as diverse as televisions, cable boxes, and home stereos. Some air conditioners can be a little more complicated, however, but [Ken]’s here to help.

The root of the problem is that the air conditioner remote was using a non-obvious checksum to verify if commands received were valid. To determine the function generating the checksum, [Ken] decided to bust out the tools of differential cryptanalysis. This involves carefully varying the input to a cryptographic function and comparing it to the differences in the output.

With 35 signals collected from the remote, a program was written to find input data that varied by just one bit. The checksum outputs were then compared to eventually put together the checksum function.

[Ken] notes that the function may not be 100% accurate, as they’re only using a limited sample of data in which not all the bytes change significantly. However, it shows that a methodical approach is valuable when approaching such projects.

Thirsty for more checksum-busting action? Check out this hacked weather station.

Building A Drone That (Almost) Follows You Home

There’s a great deal of research happening around the topic of autonomous vehicles of all creeds and colours. [Ryan] decided this was an interesting field, and took on an autonomous drone as his final project at Cornell University.

The main idea was to create a drone that could autonomously follow a target which provided GPS data for the drone to follow. [Ryan] planned to implement this by having a smartphone provide GPS coordinates to the drone over WiFi, allowing the drone to track the user.

As this was  a university project, he had to take a very carefully considered approach to the build. Given likely constraints on both money and time, he identified that the crux of the project was to develop the autonomous part of the drone, not the drone itself. Thus, off-the-shelf parts were selected to swiftly put together a drone platform that would serve as a test bed for his autonomous brain.

The write up is in-depth and shares all the gritty details of getting the various subsystems of the drone talking together. He also shares issues that were faced with altitude control – without any sensors to determine altitude, it wasn’t possible to keep the drone at a level height. This unfortunately complicated things and meant that he didn’t get to complete the drone’s following algorithm. Such roadblocks are highly common in time-limited university projects, though their educational value cannot be overstated. Overall, while the project may not have met its final goals, it was obviously an excellent learning experience, and one which has taught him plenty about working with drones and the related electronics.

For another take on autonomous flight, check out this high-speed AI racing drone.

Fill Your Hot Tub With Sand. For Science!

Here at Hackaday, we can understand if you don’t like sand. It’s coarse, rough and irritating, and it gets everywhere. With that said, [Mark Rober] discovered a great way to have fun with sand right in your own back garden.

We’ll preface this by stating that this isn’t the easiest hack to pull off on a lazy Saturday afternoon. You need a spare hot tub, plenty of pipe, and a seriously big air supply. But if you can pull it all together, the payoff is fantastic.

What [Mark] has achieved is turning a regular hot tub into a fluidized bed. In simple terms, this is where a solid particulate material (like sand) is made to act more like a fluid by passing pressurized fluid through the material. Through a carefully built series of drilled copper pipes, [Mark] manages to turn the hot tub into a fluidized bed, much to the enjoyment of his young nephews.

While it’s not the easiest hack to copy at home, [Mark] drives home the science of both the fluidized bed and why certain objects float or sink in the sand. It’s something that can also be easily tackled at a smaller scale, if you’re looking for something more achievable for the average maker.

For more sand science, how about using it to hold up your car?

[Thanks to Keith for the tip!]

Snitch On Your AC Devices With Stolen Power

Low power devices are always intriguing, as they open up possibilities for applications with the need to operate remotely, or for very long periods without attention. There are all manner of techniques for powering such devices, too, such as using solar panels, super capacitors, or other fancy devices. The Micro Power Snitch is one such device, which can report wirelessly on your AC-powered appliances.

The device is built around a tiny ARM microcontroller and an RFM69 radio module. The entire circuit is run by leeching power from an AC current transformer, wrapped around one of the power lines of an AC appliance. When an appliance draws over the minimum threshold current (500W on 230VAC, 250W on 115VAC), the device sends a packet out, which can be received and logged at the other end.

The best part of this project, however, is the writeup. The project is split into an 8-part series, breaking down the minutiae of the concepts at work to make this possible. It’s a great primer if you’re interested in designing low-power devices.

We’ve seen some of [jcw]’s power research before – such as this guide to the effects of code on power consumption.

[Thanks to Ronald for the tip!]

3D Print Yourself A Flame Thrower

For a large proportion of the world’s population, it’s now winter, which means there’s plenty of rain and snow to go around. With the surrounding environment generally cooler and wetter than usual, it’s a great time to experiment with dangerous flame based projects, like this wrist mounted flame thrower.

It’s a build that does things in both a simple and complicated way, all at once. Fuel is provided by a butane canister with a nozzle that needs to be pressed to release the gas.  A servo is used to push the canister into a 3D printed housing, releasing the gas into a pipe to guide the fuel towards the end of the user’s wrist. The fuel is then ignited by a heated coil of wire. The heated wire and the servo are both controlled by standard radio control gear typically seen on RC cars or buggies. Using the brushed speed controller to run the heated coil is particularly off-beat, but it does the job admirably.

Overall, it goes without saying that this build presents some serious risks of burns and other injuries. However, the fundamental premise is sound, and it does what it says on the tin with parts that could be readily found in the average junk box.

For another take on a wrist-mounted flame thrower, check out this version using a scavenged solenoid valve.

Lego Go-Kart Scores Radio Control

LEGO has always been an excellent toy for both play and learning, and the Technic sets are a great starting point for any budding engineer. Not content to rest on their plastic, blocky laurels, LEGO introduced more advanced parts over the years, such as motors and battery packs to allow builders to propel their creations. Combine this mechanical philosophy with [Matt]’s Giant Lego Go-Kart and you have one heck of a project.

It all started months ago, when [Matt] built his original Giant Lego Go-Kart, a 5-times scaled up model of the original kit #1972-1. Achieved through the wonder of 3D printing, he had sized it up based off the largest parts he could fit on his printer. The Youtube video led to commenters asking – could it be driven?

He decided that radio control was definitely a possibility. Not content to simply bolt on a series of motors to control the drive and steering, he took the effort to build scaled up replica LEGO motors, even taking care to emulate the old-school connectors as well. A particularly nice touch was the LEGO antenna, concealing the Orange RX radio receiver.

There were some hiccups – at this scale & with [Matt]’s parts, the LEGO force just isn’t strong enough to hold everything together. With a handful of zipties and a few squirts of glue, however, the giant ‘kart was drifting around the carpark with ease and hitting up to 26km/h.

In the end, the build is impressive not just for its performance but the attention to detail in faithfully recreating the LEGO aesthetic. As for the next step, we’d like to know what you think – how could this be scaled up to take a human driver? Is it possible? You decide.

Why You Should Use Your Router As A Security Camera

A home security camera can be great for peace of mind, and keeping an eye on the house while you’re away. The popular option these days is an IP-based device that is accessible over the Internet through an ethernet or wireless connection to your home router. But what if you could cut out the middle man, and instead turn your router itself into the security camera? [Fred] is here to show us how it’s done.

The hack begins by parsing the original router’s firmware. Through a simple text search, a debug page was identified which allowed telnet access to the router to be enabled. This gives access to a root shell, allowing full control over the Linux system running the show.

After backing everything up, [Fred] grabbed the source code from Netgear and recompiled the kernal with USB video and Video4Linux2 support. This allows the router to talk to a standard USB webcam. It’s then a simple matter of using opkg to install software to set up the router to record video when motion is detected.

Overall, it’s fairly straightforward, but [Fred] came up with an ingenious twist. Because the router itself is acting as the security camera, he is able to set up the camera to only arm itself when his smartphone (and thus, [Fred] himself) is not at home. This prevents the recording of footage of [Fred] moving around the house, allowing the router to only record important footage for security purposes.

It’s possible to do great things with routers – most of them are just tiny boxes running Linux anyway. Check out this one used as an online energy meter.