Chua’s circuit is the simplest electronic circuit that produces chaos—the output of this circuit never repeats the same sequence, and is a truly random signal. If you need a good source of randomness, Chua’s circuit is easy to make and is built around standard components that you might have lying around. [Valentine] wrote a comprehensive guide which walks you through the process of building your own source of chaos.
The chaos of Chua’s circuit is derived from several elements, most importantly a nonlinear negative resistor. Unfortunately for us, this type of resistor doesn’t exist in a discrete form, so we have to model it with several other components. This resistor, also known as Chua’s diode, can be created with an op-amp configured as a negative impedance converter and a couple pairs of diodes and resistors. Other variations such, as the schematic above,22`01 model Chua’s diode using only op-amps and resistors.
The rest of the circuit is quite simple: only two capacitors, an inductor, and a resistor are needed. [Valentine] does note that the circuit is quite sensitive, so you might encounter issues when building it on a breadboard. The circuit is very sensitive to vibration (especially on a breadboard), and good solder connections are essential to a reliable circuit. Be sure to check out the Wikipedia article on Chua’s circuit for a brief overview of the circuit’s functionality and a rabbit trail of information on chaos theory.
[HeadlessZeke] was excited to try out his new AT&T wireless cable box, but was quickly dismayed by the required wireless access point that came bundled with it. Apparently in order to use the cable box, you also need to have this access point enabled. Not one to blindly put unknown devices on his network, [HeadlessZeke] did some investigating.
The wireless access point was an Arris VAP2500. At first glance, things seemed pretty good. It used WPA2 encryption with a long and seemingly random key. Some more digging revealed a host of security problems, however.
It didn’t take long for [HeadlessZeke] to find the web administration portal. Of course, it required authentication and he didn’t know the credentials. [HeadlessZeke] tried connecting to as many pages as he could, but they all required user authentication. All but one. There existed a plain text file in the root of the web server called “admin.conf”. It contained a list of usernames and hashed passwords. That was strike one for this device.
[HeadlessZeke] could have attempted to crack the passwords but he decided to go further down this rabbit hole instead. He pulled the source code out of the firmware and looked at the authentication mechanism. The system checks the username and password and then sets a cookie to let the system know the user is authenticated. It sounds fine, but upon further inspection it turned out that the data in the cookie was simply an MD5 hash of the username. This may not sound bad, but it means that all you have to do to authenticate is manually create your own cookie with the MD5 hash of any user you want to use. The system will see that cookie and assume you’ve authenticated. You don’t even have to have the password! Strike two.
Now that [HeadlessZeke] was logged into the administration site, he was able to gain access to more functions. One page actually allows the user to select a command from a drop down box and then apply a text argument to go with that command. The command is then run in the device’s shell. It turned out the text arguments were not sanitized at all. This meant that [HeadlessZeke] could append extra commands to the initial command and run any shell command he wanted. That’s strike three. Three strikes and you’re out!
[HeadlessZeke] reported these vulnerabilities to Arris and they have now been patched in the latest firmware version. Something tells us there are likely many more vulnerabilities in this device, though.
Have some .40 cal shell casings sitting around with nothing to do? How about some bullet earbuds? If you’ve ever wondered about the DIY community over at imgur, the top comment, by a large margin, is, “All of these tools would cost so much more than just buying the headphones”
Here’s something [Lewin] sent in. It’s a USB cable, with a type A connector on one end, and a type A connector on the other end. There is no circuitry anywhere in this cable. This is prohibited by the USB Implementors Forum, so if you have any idea what this thing is for, drop a note in the comments.
Attention interesting people in Boston. There’s a lecture series this Tuesday on Artificial Consciousness and Revolutionizing Medical Device Design. This is part two in a series that Hackaday writer [Gregory L. Charvat] has been working with. Talks include mixed signal ASIC design, and artificial consciousness as a state of matter. Free event, open bar, and you get to meet (other) interesting people.
Ghostbusters. It’s the 30th anniversary, and to celebrate the event [Luca] is making a custom collectors edition with the BluRay and something very special: the Lego ECTO-1.
Let’s say you need to store the number of days in each month in a program somewhere. You could look it up in the Time Zone Database, but that’s far too easy. How about a lookup table, or just a freakin’ array with 12 entries? What is this, amateur hour? No, the proper way of remembering the number of days in each month is some bizarre piece-wise function. It is: f(x) = 28 + (x + ⌊x⁄8⌋) mod 2 + 2 mod x + 2 ⌊1⁄x⌋. At least the comments are interesting.
Arduinos were sold in the 70s! Shocking, yes, but don’t worry, time travel was involved. Here’s a still from Predestination, in theatres Jan 9, rated R, hail corporate.
Ever heard of the summer camp called Superhero Cyborgs? It’s where [Coby Unger] met nine-year-old [Aidan Robinson] and helped him design his very own custom prosthetic arm.
The camp is put on by KIDmob for kids who have various limb disabilities, and helps give them the tools and guidance to be able to make their very own prosthetics. Some of the designs the children come up with are cool, useful, pretty and sometimes not overly functional — but [Aidan’s] designs really intrigued [Coby] who is a designer and part of the staff at Pier 9, a world-class fabrication facility (and makerspace) run by Autodesk.
There’s a lot of problems with prosthetics for children. They’re very expensive, kids don’t stay the same size, and even though they might cost a lot, they don’t necessarily work that well. [Aidan] had a few commercial options but didn’t like any of them, so much so that he preferred not wear them period. But when he attended the camp he realized he had the ability to design a prosthetic that he’d actually want to wear.
Continue reading “Kid Designs His Own Prosthetic Arm At A Summer Camp”
A few years ago, the world of fine woodworking was presented with the Fletcher Capstan table. It’s a round table, able to expand its diameter merely by rotating the top. A gloriously engineered bit of mechanics move the leaves of the tables out while simultaneously raising the inner part of the table. It’s a seriously cool table, very expensive, and something that will probably be found in museums 100 years from now.
[Scott Rumschlag] thought his woodworking skills were up to the task of creating one of these expanding tables and managed to build one in his workshop. Like the Fletcher Capstan table, it’s a table that increases its diameter simply by rotating the table top. Unlike the commercial offering, this one doesn’t cost as much as a car, and you can actually see the internal mechanism inside this table.
The top of [Scott]’s table is made of three pieces. The quarter-circle pieces are the only thing showing when the table is in its minimum position, and are arranged on the top of the ‘leaf stack’. When the table expands, four additional leaves move up from beneath with the help of a linear bearing made of wood and a roller that slides along the base of this mechanical contraption.
The center of the table – the star – is a bit more difficult to design. While the leaves move up the stack of table tops with the help of a ramp, this is an impractical solution for something so close to the center of the table. Instead of a ramp, [Scott] is using a lifting lever and metal hinge that brings the star of the table up to the right level. Even though it’s a crazy amount of woodworking and fine tuning to get everything right, it’s not too terribly difficult to get your head around.
Videos, including one of the assembly of the table, below.
Continue reading “An Expanding Wooden Table”
This schematic is all you need to build your own voltage converter. [Lutz] needed a converter that could boost 5 V to 30 V to power a string of LEDs. The solution was to use low cost ATtiny85 and some passive components to implement a boost converter.
This circuit follows the classic boost converter topology, using the ATtiny85 to control the switch. The 10 ohm resistor is fed back into the microcontroller’s ADC input, allowing it to sense the output voltage. By measuring the output voltage and adjusting the duty cycle accordingly, the circuit can regulate to a specified voltage setpoint.
A potentiometer is used to change the brightness of the LEDs. The software reads the potentiometer’s output voltage and adjusts the voltage output of the circuit accordingly. Higher voltages result in brighter LEDs.
Of course, there’s many other ways to implement a boost converter. Most practical designs will use a chip designed for this specific purpose. However, if you’re interested in rolling your own, the source and LTSpice simulation files are available.