Misc Hacks

4173 Articles

Easier UART To 1-Wire Interface

January 29, 2015 by 28 Comments

The 1-Wire protocol is usually found in temperature sensors, but you’ll also find it in chips ranging from load sensors, a battery sensor and LED driver that is oddly yet officially called a ‘gas gauge’, and iButtons. It’s a protocol that has its niche, and there are a few interesting application notes for implementing the 1-wire protocol with a UART. Application notes are best practices, but [rawe] has figured out an even easier way to do this.

The standard way of reading 1-Wire sensors with a UART is to plop a pair of transistors and resistors on the Tx and Rx lines of the UART and connect them to the… one… wire on the 1-Wire device. [rawe]’s simplification of this is to get rid of the transistors and just plop a single 1N4148 diode in there.

This would of course be useless without the software to communicate with 1-Wire devices, and [rawe] has you covered there, too. There’s a small little command line tool that will talk to the usual 1-Wire temperature sensors. Both the circuit and the tool work with the most common USB to UART adapters.

hassler_pcb

Annoy Your Enemies With The Hassler Circuit

January 29, 2015 by 62 Comments

[Craig] recently built himself a version of the “hassler” circuit as a sort of homage to Bob Widlar. If you haven’t heard of Bob Widlar, he was a key person involved in making analog IC’s a reality. We’ve actually covered the topic in-depth in the past. The hassler circuit is a simple but ingenious office prank. The idea is that the circuit emits a very high frequency tone, but only when the noise level in the room reaches a certain threshold. If your coworkers become too noisy, they will suddenly notice a ringing in their ears. When they stop talking to identify the source, the noise goes away. The desired result is to get your coworkers to shut the hell up.

[Craig] couldn’t find any published schematics for the original circuit, but he managed to build his own version with discrete components and IC’s. Sound first enters the circuit via a small electret microphone. The signal is then amplified, half-wave rectified, and run through a low pass filter. The gain from the microphone is configurable via a trim pot. A capacitor converts the output into a flat DC voltage.

The signal then gets passed to a relaxation oscillator circuit. This circuit creates a signal whose output duty cycle is dependent on the input voltage. The higher the input voltage, the longer the duty cycle, and the lower the frequency. The resulting signal is sent to a small speaker for output. The speaker is also controlled by a Schmitt trigger. This prevents the speaker from being powered until the voltage reaches a certain threshold, thus saving energy. The whole circuit is soldered together dead bug style and mounted to a copper clad board.

When the room is quiet, the input voltage is low. The output frequency is high enough that it is out of the range of human hearing. As the room slowly gets louder, the voltage increases and the output frequency lowers. Eventually it reaches the outer limits of human hearing and people in the room take notice. The video below walks step by step through the circuit. Continue reading “Annoy Your Enemies With The Hassler Circuit” →

When Adding Noise Helps

January 25, 2015 by 20 Comments

It’s a counterintuitive result that you might need to add noise to an input signal to get the full benefits from oversampling in analog to digital conversion. [Paul Allen] steps us through a simple demonstration (dead link, try Internet Archive) of why this works on his blog. If you’re curious about oversampling, it’s a good read.

Oversampling helps to reduce quantization noise, which is the sampling equivalent of rounding error. In [Paul’s] one-bit ADC example, the two available output values are zero volts and one volt. Any analog signal between these two values is rounded off to either zero or one, and the resulting difference is the quantization error.

In oversampling, instead of taking the bare minimum number of samples you need you take extra samples and average them together. But as [Paul] demonstrates, this only works if you’ve got enough noise in the system already. If you don’t, you can actually make your output more accurate by adding noise on the input. That’s the counterintuitive bit.

We like the way he’s reduced the example to the absolute minimum. Instead of demonstrating how 16x oversampling can add two bits of resolution to your 10-bit ADC, it’s a lot clearer with the one-bit example.

[Paul’s] demo is great because it makes a strange idea obvious. But it got us just far enough to ask ourselves how much noise is required in the system for oversampling to help in reducing quantization noise. And just how much oversampling is necessary to improve the result by a given number of bits? (The answers are: at least one bit’s worth of noise and 22B, respectively, but we’d love to see this covered intuitively.) We’re waiting for the next installment, or maybe you can try your luck in the comment section.

Real World AdBlock

January 23, 2015 by 42 Comments

Every day your eyeballs are assaulted by advertisements on your box of cereal, billboards, t-shirts, magazines, milk cartons, plastered on the side of buses, buildings, bananas, and written in the sky. [Reed], [Jonathan], [Tom], and [Alex] came up with a solution to this: a Brand Killer that censors all the advertisements and brands you see every minute of every day. It’s a real-world adblock that you can build right now.

The team’s system uses a custom head mounted display made from cardboard, goggles, a webcam, and a seven-inch display. The software for the system uses Python and OpenCV to monitor the images from the webcam, compares them against a list of brands and logos, and filters them out with an unobtrusive blur.

Right now the system just has a few brands and logos that include Dr. Pepper, Hershey’s, McDonalds, Facebook, Starbucks, and clear evidence this was built at UPenn, Wawa and Tastykake. In the video below, the detection and tracking of these various brands is very good. The system is also stereoscopic, meaning this is wearable all day, every day, without a loss of depth perception.

Continue reading “Real World AdBlock” →

Adjustable Desk

An Adjustable Sit/Stand Desk For Under $100

January 23, 2015 by 33 Comments

[Cornel Masson] is a 46-year-old computer programmer. He’s been working on his computer for the last 30 years. Computer work can be good for the wallet but it can be bad for our health, particularly the neck and back. You can purchase adjustable desks to allow you to change positions from sitting to standing, but unfortunately these desks are often expensive. [Cornel] took matters into his own hands and build his own adjustable riser for under $100.

To start, [Cornel] used a typical computer desk. He didn’t want to build the entire thing from scratch. Instead he focused on building a riser that sits on top of the desk, allowing him to change the height of both the monitor and keyboard. His design used mostly wood, aluminum stock, threaded rods, and drawer slides.

The main component is the monitor stand and riser. The riser is able to slide up and down thanks to four drawer slides mounted vertically. [Cornel] wanted his monitor to move up and down with ease, which meant he needed some kind of counter weight. He ended up using a gas strut from the trunk of a Nissan, which acts as a sort of spring. The way in which it is mounted makes for a very close approximation of his monitor’s weight. The result is a monitor that can be raised or lowered very easily. The stand also includes a locking mechanism to keep it secured in the top position.

The keyboard stand is also mounted to drawer slides, only these are in the horizontal position. When the monitor is lowered for sitting, the keyboard tray is removed from the keyboard stand. The stand can then be pushed backwards, overlapping the monitor stand and taking up much less space. The keyboard stand has small rollers underneath to help with the sliding. The video below contains a slideshow of images that do a great job explaining how it all works.

Of course if replacing the entire desk is an option go nuts.

Continue reading “An Adjustable Sit/Stand Desk For Under $100” →

Laser Etched Surface Redefines Dry

January 22, 2015 by 89 Comments

Just the other day we stood in the kitchen making eggs, staring suspiciously at a long scratch carved in the center of the frying pan. With all the articles passing through social media prompting us to be wary of things in our environment that are supposedly killing us, Teflon included, I wondered to myself if humans would ever start coming up with solutions to daily problems… like sticky eggs, which don’t involve the use of complex chemicals. Alas, the universe responds with uncanny timing. A group of researchers led by [Chunlei Guo] from Rochester University’s Institute of Optics has recently published their development of a surface textured by lasers which repels fluid like a rubber ball… without any chemical treating involved. You really need to see this happen in the video below.

This physical magic trick gets its inspiration from nature, mimicking properties of surface tension from living things that repel water such as lotus leaves or butterfly wings. To achieve a similar effect, a precision laser is used to etch nanoscale patterns onto metal which change the surface properties in such a way that fluid molecules prefer not to stick. The benefit to texturizing a material’s surface as opposed to glazing it in some other repellant, is that the pattern becomes intrinsically part of the surface structure and will not fade over time the way a chemical seal will chip or flake. This hydrophobic technology could improve the way we keep surfaces sanitary as well as lend itself to new methods of frost prevention. Not to mention the dozens of other less important applications that we’ve just thought of for our own amusement.

In addition to creating the hydrophobic surface, the Institute of Optic has employed similar tactics to come up with a material capable of absorbing fluid and carrying it upward swiftly against gravity. With the knowledge of physics and the power of lasers combined, we’re glad to see humans coming up with smarter ways to manipulate the world we live in for a more comfortable daily life.

Continue reading “Laser Etched Surface Redefines Dry” →

Spliced Animations Come To Life On Their Pages

January 16, 2015 by 15 Comments

Remember those flipbooks you doodled into your history textbooks while you waited for the lunch bell? [Maric] takes the general principles of flipbooks and turns them on their head, giving our brain a whirl in the process. By splicing multiple frames into one image, he can bring animations to life onto a single page.

The technique is simple, but yields impressive results. By overlaying a pattern of vertical black bars onto his image, only a small fraction of the image is visible at any given point. The gaps in the pattern belong to a single frame from the animation. As [Maric] slides the pattern over the image, subsequent frames are revealed to our eyes, and our brain fills in the rest.

A closer look reveals more detail about the constraints imposed on these animations. In this case, the number of frames per animation loop is given by the widths in the transparency pattern. Specifically, it is the number of transparent slits that could fit, side-by-side, within an adjacent black rectangle.

The trick that makes this demonstration work so nicely is that the animated clips finish where they start, resulting in a clean, continuous illusion.

Don’t believe what you see? [Maric] has linked the pattern and images on his video so you can try them for yourself. Give them a go, and let us know what you think in the comments.

Continue reading “Spliced Animations Come To Life On Their Pages” →